Every person has admired the stars at least once in their life while looking at the night sky. They are mysterious, attractive, and have many interesting facts associated with them.
We all know that the Moon is a satellite of the Earth. However little known fact it is believed that it is always turned with one side towards our planet. The “dark” side of the satellite causes a lot of controversy among scientists and regularly becomes the reason for the emergence of amazing theories about the existence of extraterrestrial civilizations.
The daytime temperature on the surface of Venus is about 425 degrees.
On the Moon, the highest temperature reaches +116 degrees, the lowest drops to -164 degrees. The Earth's satellite is four hundred times smaller than the Sun and four hundred times closer to our planet.
Earth is the only planet not named after an ancient deity.
It takes the Moon just over 27 days to orbit the Earth. Our planet revolves around the Sun in one year (365 days). It takes eight and a half minutes for light from the Sun to reach us.
The weight of our planet is about 600 trillion tons.
The number of members of the unique computer program SETI, which provides the opportunity for every user of the World Wide Web to take part in the search for aliens, is more than three million.
Studying interesting facts about stars and planets, scientists came to the conclusion that the volume of Saturn is 758 times larger than the Earth. However, this planet is incredibly light. If you put it in the largest aquarium with water, it will begin to float on its surface.
Ceres is the largest asteroid. Its radius is about 470 kilometers. It is the first asteroid to be discovered by man. It was the Italian Piazzi. This amazing event happened in January 1801.
Modern scientists divide the sky into eighty-eight sectors. They are usually called constellations. Another interesting fact about stars is that the Sun moves across the Galaxy at a speed of 250 kilometers per second. Compared to our planet, its weight is 333 thousand times greater. It takes the Sun two hundred million years to fly around the center of the Galaxy.
This star is 30% helium and 70% hydrogen. Its radius is approximately 218 times the diameter of the Earth.
The human eye can distinguish up to 5,000 stars in the sky. Experts believe that there are about 410 billion stars in our galaxy.
Every year, several thousand kilograms of interplanetary dust end up on our planet.
Our solar system is located in the spiral arm of the Milky Way. It consists not only of stars, but also of dust and gas.
7 stars are located at a distance of ten light years from Earth. Proxima, part of the Alpha Centauri system, is considered to be closest to us.
The mass of our planet has increased by 1 billion tons over the past five hundred years. The reason for this is the influence of cosmic matter.
The height of the hills on Mars is 21-26 kilometers. The atmosphere there is 95% carbon monoxide.
An amazing fact is that approximately 200 thousand meteorites fall on our planet every day.
The planet Uranus can be seen from the surface of the Earth. It is important that you do not need to use special equipment for this. It can be seen with the naked eye. However, this is possible under good weather conditions and on a moonless night.
Interesting video about Space in the video. Amazing facts:
13.04.2014
Stars have been fascinating subjects of study throughout history. From the ancient Greeks to our modern astronomers, people are constantly looking for new stars, other planets and galaxies. AND interesting facts about stars always intrigue us. The universe is constantly expanding and also changing, so every time an astronomer looks through a telescope, he can see something that wasn't there the day before! And in this place, so full of wonder and so much unknown, there are tons of facts about the stars. We would like to present you our top 10 the most interesting facts about stars.
No. 10. Red dwarfs:
The most common stars in the universe are red dwarfs. This is largely due to their low mass, which allows them to live for a very long time before becoming white dwarfs.
No. 9. Chemical composition of stars:
Almost all stars in the universe have the same chemical composition and reaction nuclear fusion occurs in every star and is almost identical, determined only by the amount of fuel.
No. 8. Neutron stars:
As we know, like a white dwarf, neutron stars are one of the final processes of stellar evolution, largely arising after a supernova explosion. Previously, it was often difficult to distinguish a white dwarf from a neutron star, but now scientists are using
telescopes found differences in them. Neutron star gathers around itself more light and it is easy to see with infrared telescopes. Eighth place among interesting facts about stars.
No. 7. Black hole:
Thanks to its incredible mass, according to general theory According to Einstein's relativity, a black hole is actually a bend in space such that everything within its gravitational field is pushed towards it. The gravitational field of a black hole is so strong that not even light can escape it.
No. 6. Massive star:
As far as we know, when a star runs out of fuel, the star can grow in size by more than 1000 times, then it turns into a white dwarf, and due to the speed of the reaction, it explodes. This reaction is better known as a supernova. Scientists suggest that due to this long process, such mysterious black holes are formed.
No. 5. Confluence of stars in the sky:
Many of the stars we see in the night sky can appear as just one glimpse of light. However, this is not always the case. Most of the stars we see in the sky are actually two star systems, or binary star systems. They are simply unimaginably far away and it seems to us that we see only one speck of light.
No. 4. Lifespan of stars:
The stars that have the shortest lifespans are the most massive. They are a high mass of chemicals and tend to burn their fuel much faster.
No. 3. Twinkling stars:
Despite the fact that sometimes it seems to us that the Sun and stars are twinkling, in fact this is not the case. The flickering effect is only the light from the star, which at this time passes through the Earth's atmosphere but has not yet reached our eyes. Third place among the most interesting facts about stars.
No. 2. Huge distances to the stars:
The distances involved in estimating how far away a star is are unimaginably huge. Let's consider an example: The closest star to earth is approximately 4.2 light years away, and to get to it, even on our fastest ship, will take about 70,000 years.
No. 1. Temperature of stars:
The coolest known star is the brown dwarf CFBDSIR 1458+10B, which has a temperature of only about 100 °C.
The hottest known star, a blue supergiant in the Milky Way called Zeta Puppis, has a temperature of over 42,000 °C.
From time immemorial, Man tried to give names to the objects and phenomena that surrounded him. This also applies to celestial bodies. First, the brightest, clearly visible stars were given names, and over time, others were given names.
Some stars are named according to the position they occupy in the constellation. For example, the star Deneb (the word translates as “tail”) located in the constellation Cygnus is actually located in this part of the body of an imaginary swan. One more example. The star Omicron, better known as Mira, which translates from Latin as “amazing,” is located in the constellation Cetus. Mira has the ability to change its brightness. For long periods it completely disappears from view, meaning observations with the naked eye. The name of the star is explained by its specificity. Basically, stars received names in the era of antiquity, so it is not surprising that most of the names have Latin, Greek, and later Arabic roots.
The discovery of stars whose apparent brightness changes over time led to special designations. They are designated by capital Latin letters, followed by the name of the constellation in genitive case. But the first variable star discovered in a certain constellation is not designated by the letter A. The countdown is from the letter R. The next star is designated by the letter S, and so on. When all the letters of the alphabet are exhausted, a new circle begins, that is, after Z, A is used again. In this case, letters can be doubled, for example “RR”. "R Leo" means it is the first variable star discovered in the constellation Leo.
HOW A STAR IS BORN.
Stars are born when a cloud of interstellar gas and dust is compressed and compacted by its own gravity. It is believed that this process leads to the formation of stars. Using optical telescopes, astronomers can see these zones; they look like dark spots against a bright background. They are called "giant molecular cloud complexes" because hydrogen is present in molecular form. These complexes, or systems, along with globular star clusters, represent the most large structures in the galaxy, their diameter sometimes reaches 1300 light years.
Younger stars, called "stellar population I", were formed from the remnants resulting from the outbursts of older stars, they are called "stellar population II". An explosive outbreak causes shock wave, which reaches the nearest nebula and provokes its compression.
Bock globules .
So, part of the nebula is compressed. Simultaneously with this process, the formation of dense dark round gas and dust clouds begins. They are called "Bock globules". Bok, an American astronomer of Dutch origin (1906-1983), was the first to describe globules. The mass of the globules is approximately 200 times the mass of our Sun.
As the Bok globule continues to condense, its mass increases, attracting matter from neighboring regions due to gravity. Due to the fact that the inner part of the globule condenses faster than the outer part, the globule begins to heat up and rotate. After several hundred thousand years, during which compression occurs, a protostar is formed.
Evolution of a protostar.
Due to the increase in mass, more and more matter is attracted to the center of the protostar. The energy released from the gas compressed inside is transformed into heat. The pressure, density and temperature of the protostar increase. Due to the increase in temperature, the star begins to glow dark red.
The protostar has a very big sizes, and although thermal energy distributed over its entire surface, it still remains relatively cold. In the core, the temperature rises and reaches several million degrees Celsius. The rotation and round shape of the protostar change somewhat, it becomes flatter. This process lasts millions of years.
It is difficult to see young stars, since they are still surrounded by a dark dust cloud, due to which the brightness of the star is practically invisible. But they can be viewed using special infrared telescopes. The hot core of a protostar is surrounded by a rotating disk of matter with a strong gravitational force. The core gets so hot that it begins to eject matter from the two poles, where resistance is minimal. When these emissions collide with the interstellar medium, they slow down and disperse on either side, forming a teardrop-shaped or arched structure known as a Herbic-Haro object.
Star or planet?
The temperature of a protostar reaches several thousand degrees. Further developments depend on the dimensions of this celestial body; if the mass is small and is less than 10% of the mass of the Sun, this means that there are no conditions for nuclear reactions to occur. Such a protostar will not be able to turn into a real star.
Scientists have calculated that for a contracting celestial body to transform into a star, its minimum mass must be at least 0.08 of the mass of our Sun. A gas-containing cloud of smaller sizes, condensing, will gradually cool and turn into a transitional object, something between a star and a planet, this is the so-called “brown dwarf”.
The planet Jupiter is a celestial object too small to become a star. If it had been larger, perhaps in its depths there would have begun nuclear reactions, and it, along with the Sun, would contribute to the emergence of a system of double stars.
Nuclear reactions.
If the mass of a protostar is large, it continues to condense under the influence of its own gravity. The pressure and temperature in the core increase, the temperature gradually reaches 10 million degrees. This is enough to combine hydrogen and helium atoms.
Next, “ nuclear reactor" protostar, and it turns into an ordinary star. A strong wind is then released, which disperses the surrounding shell of dust. Light can then be seen emanating from the resulting star. This stage is called the "T-Taurus phase" and can last 30 million years. The formation of planets is possible from the remnants of gas and dust surrounding the star.
Birth nova may cause a shock wave. Having reached the nebula, it provokes the condensation of new matter, and the star formation process will continue through gas and dust clouds. Small stars are faint and cold, while large stars are hot and bright. For most of its existence, the star balances in the equilibrium stage.
CHARACTERISTICS OF STARS.
Observing the sky even with the naked eye, you can immediately notice such a feature of the stars as brightness. Some stars are very bright, others are fainter. Without special devices V ideal conditions visibility, you can see about 6000 stars. Thanks to binoculars or a telescope, our capabilities increase significantly; we can admire millions of stars in the Milky Way and outer galaxies.
Ptolemy and the Almagest.
The first attempt to compile a catalog of stars, based on the principle of their degree of luminosity, was made by the Hellenic astronomer Hipparchus of Nicaea in the 2nd century BC. Among his numerous works was the Star Catalog, containing a description of 850 stars classified by coordinates and luminosity. The data collected by Hipparchus, who, in addition, discovered the phenomenon of precession, was processed and received further development thanks to Claudius Ptolemy from Alexandria in the 2nd century. AD He created the fundamental opus “Almagest” in thirteen books. Ptolemy collected all the astronomical knowledge of that time, classified it and presented it in an accessible and understandable form. The Almagest also included the Star Catalog. It was based on observations made by Hipparchus four centuries ago. But Ptolemy's Star Catalog contained about a thousand more stars.
Ptolemy's catalog was used almost everywhere for a millennium. He divided stars into six classes according to the degree of luminosity: the brightest were assigned to the first class, the less bright to the second, and so on.
The sixth class includes stars that are barely visible to the naked eye. The term “luminosity of celestial bodies” is still used today to determine the measure of brilliance of celestial bodies, not only stars, but also nebulae, galaxies and others. celestial phenomena.
Magnitude in modern science.
In the middle of the 19th century. English astronomer Norman Pogson improved the method of classifying stars based on the principle of luminosity, which had existed since the times of Hipparchus and Ptolemy. Pogson took into account that the difference in luminosity between the two classes is 2.5. Pogson introduced a new scale according to which the difference between stars of the first and sixth classes is 100 AU. That is, the brightness ratio of stars of the first magnitude is 100. This ratio corresponds to an interval of 5 magnitudes.
Relative and absolute magnitude.
Magnitude, measured using special instruments mounted in a telescope, indicates how much light from a star reaches an observer on Earth. Light travels the distance from the star to us, and, accordingly, the further away the star is, the fainter it appears. That is, when determining stellar magnitude, it is necessary to take into account the distance to the star. IN in this case We are talking about relative stellar magnitude. It depends on the distance.
There are very bright and very faint stars. To compare the brightness of stars, regardless of their distance from the Earth, the concept of “absolute stellar magnitude” was introduced. It characterizes the brightness of a star at a certain distance of 10 parsecs (10 parsecs = 3.26 light years). To determine the absolute magnitude, you need to know the distance to the star.
The color of the stars.
The next important characteristic of a star is its color. Looking at the stars even with the naked eye, you can see that they are not all the same.
There are blue, yellow, orange, red stars, not just white ones. The color of stars tells a lot to astronomers, primarily depending on the temperature of the star's surface. Red stars are the coldest, their temperature is approximately 2000-3000 o C. Yellow stars, like our Sun, have an average temperature of 5000-6000 o C. The hottest are white and blue stars, their temperature is 50000-60000 o C and higher .
Mysterious lines.
If we pass starlight through a prism, we get a so-called spectrum; it will be intersected by lines. These lines are a kind of “identification card” of the star, since astronomers can use them to determine the chemical composition of the surface layers of stars. The lines belong to different chemical elements.
By comparing the lines in the stellar spectrum with lines made in the laboratory, it is possible to determine which chemical elements are included in the composition of stars. In the spectra, the main lines are hydrogen and helium; it is these elements that make up the main part of the star. But there are also elements of the metal group - iron, calcium, sodium, etc. In the bright solar spectrum, lines of almost all chemical elements.
HERZSPRUNG-RUSSELL DIAGRAM.
Among the parameters characterizing a star, there are two most important ones: temperature and absolute magnitude. Temperature indicators are closely related to the color of the star, and the absolute magnitude is closely related to the spectral type. This refers to the classification of stars according to the intensity of the lines in their spectra. According to the classification currently used, stars are divided into seven main spectral classes according to their spectra. They are designated by the Latin letters O, B, A, F, G, K, M. It is in this sequence that the temperature of stars decreases from several tens of thousands of degrees of class O to 2000-3000 degrees of type M stars.
Absolute magnitude, i.e. A measure of brightness that indicates the amount of energy emitted by a star. It can be calculated theoretically, knowing the distance of the star.
Outstanding idea.
The idea to connect the two main parameters of a star came to the minds of two scientists in 1913, and they carried out work independently of each other.
We are talking about the Dutch astronomer Einar Hertzsprung and the American astrophysicist Henry Norris Russell. Scientists worked at a distance of thousands of kilometers from each other. They created a graph that linked together the two main parameters. The horizontal axis reflects the temperature, the vertical axis – the absolute magnitude. The result was a diagram that was given the names of two astronomers - the Hertzsprung-Russell diagram, or, more simply, the H-R diagram.
Star is a criterion.
Let's see how the G-R diagram is made. First of all, you need to select a criterion star. A star whose distance is known, or another with an already calculated absolute magnitude, is suitable for this.
It should be borne in mind that the luminous intensity of any source, be it a candle, a light bulb or a star, changes depending on the distance. This is expressed mathematically as follows: the luminosity intensity “I” at a certain distance “d” from the source is inversely proportional to “d2”. In practice, this means that if the distance doubles, the luminosity intensity decreases fourfold.
Then the temperature of the selected stars should be determined. To do this, you need to identify their spectral class, color and then determine the temperature. Currently, instead of the spectral type, another equivalent indicator is used - the “color index”.
These two parameters are plotted on the same plane with the temperature decreasing from left to right on the abscissa. The absolute luminosity is fixed at the ordinate, an increase is noted from bottom to top.
Main sequence.
On a H-R diagram, stars are located along a diagonal line running from bottom to top and from left to right. This strip is called the Main Sequence. The stars that make up it are called Main Sequence stars. The sun belongs to this group. This group yellow stars with a surface temperature of approximately 5600 degrees. Main Sequence stars are in the most “quiet phase” of their existence. In the depths of their nuclei, hydrogen atoms mix and helium is formed. The Main Sequence phase accounts for 90% of a star's lifetime. Out of 100 stars, 90 are in this phase, although they are distributed in different positions depending on temperature and luminosity.
The main sequence is a “narrow region,” indicating that stars have difficulty maintaining a balance between the force of gravity, which pulls inward, and the force generated by nuclear reactions, which pulls toward the outside of the zone. A star like the Sun, equal to 5600 degrees, must have an absolute magnitude of about +4.7 to maintain balance. This follows from the G-R diagram.
Red giants and white dwarfs.
Red giants are in the upper zone on the right, located with outside Main sequence. A characteristic feature of these stars is that they are very low temperature(about 3000 degrees), but at the same time they are brighter than stars that have the same temperature and are located in the Main Sequence.
Naturally, the question arises: if the energy emitted by a star depends on temperature, then why do stars with the same temperature have different degrees of luminosity. The explanation should be sought in the size of the stars. Red giants are brighter because their emitting surface is much larger than that of Main Sequence stars.
It is no coincidence that this type of star is called “giant”. Indeed, their diameter can exceed the diameter of the Sun by 200 times; these stars can occupy a space of 300 million km, which is double more distance from Earth to Sun! Using the statement about the influence of the size of a star, we will try to explain some aspects in the existence of other stars - white dwarfs. They are located at the bottom left of the H-R diagram.
White dwarfs are very hot, but very dim stars. At the same temperature as the large and hot blue-white stars of the Main Sequence, white dwarfs are much smaller in size. These are very dense and compact stars, they are 100 times smaller than the Sun, their diameter is approximately the same as that of Earth. You can cite shining example high density white dwarfs – one cubic centimeter the matter of which they are composed must weigh about one ton!
Globular star clusters.
When compiling HR diagrams of globular star clusters, and they contain mainly old stars, it is very difficult to determine the Main Sequence. Its traces are recorded mainly in the lower zone, where cooler stars are concentrated. This is due to the fact that hot and bright stars have already passed the stable phase of their existence and are moving to the right, into the red giant zone, and if they have passed it, then into the white dwarf zone. If people were able to trace all the evolutionary stages of a star over its life, they would be able to see how it changes its characteristics.
For example, when hydrogen in the core of a star stops burning, the temperature in the outer layer of the star decreases, and the layer itself expands. The star is leaving the Main Sequence phase and heading to the right side of the diagram. This applies primarily to stars that are large in mass and the brightest; it is this type that evolves faster.
Over time, stars move out of the Main Sequence. The diagram records a “turning point”, thanks to which it is possible to quite accurately calculate the age of the stars in clusters. The higher the “turning point” is on the diagram, the younger the cluster, and, accordingly, the lower it is on the diagram, the older the star cluster.
The meaning of the chart.
The Hertzsprung-Russell diagram is of great help in studying the evolution of stars throughout their existence. During this time, the stars undergo changes and transformations, and in some periods they are very profound. We already know that stars differ not in their own characteristics, but in the types of phases in which they are at one time or another.
Using this diagram you can calculate the distance to the stars. You can select any star located in the Main Sequence with an already determined temperature and see its progress on the diagram.
DISTANCE TO THE STARS.
When we look at the sky with the naked eye, stars, even the brightest ones, seem to us to be shiny points located at the same distance from us. The vault of heaven spreads out over us like a carpet. It is no coincidence that the positions of the stars are expressed in only two coordinates (right ascension and declination), and not in three, as if they are located on the surface and not in three-dimensional space. With the help of telescopes, we cannot obtain all the information about the stars; for example, from photographs of the Hubble Space Telescope, we cannot accurately determine at what distance the stars are located.
Depth of space.
People learned relatively recently that the Universe also has a third dimension – depth. Only at the beginning of the 19th century, thanks to the improvement of astronomical equipment and instruments, scientists were able to measure the distance to some stars. The first was the star 61 Cygni. Astronomer F.V. Bessel found that it was at a distance of 10 light years. Bessel was one of the first astronomers to measure the "annual parallax". Until now, the “annual parallax” method has been the basis for measuring the distance to stars. This is a purely geometric method - just measure the angle and calculate the result.
But the simplicity of the method does not always correspond to effectiveness. Due to the great distance of the stars, the angles are very small. They can be measured using telescopes. The parallax angle of the star Proxima Centauri, the closest of the triple system Alpha Centauri, is small (0.76 exact version), but from this angle you can see a hundred lire coin at a distance of ten kilometers. Of course, the further the distance, the smaller the angle becomes.
Inevitable inaccuracies.
Errors in terms of determining parallax are quite possible, and their number increases as the object moves away. Although, with the help of modern telescopes, it is possible to measure angles with an accuracy of one thousandth, there will still be errors: at a distance of 30 light years they will be approximately 7%, 150 light years. years - 35%, and 350 St. years – up to 70%. Of course, large inaccuracies render measurements useless. Using the “parallax method”, it is possible to successfully determine the distances to several thousand stars located in an area of approximately 100 light years. But in our galaxy there are more than 100 billion stars, the diameter of which is 100,000 light years!
There are several variations of the annual parallax method, such as secular parallax. The method takes into account the movement of the Sun and the entire solar system in the direction of the constellation Hercules, at a speed of 20 km/sec. With this movement, scientists have the opportunity to collect the necessary database to carry out a successful parallax calculation. In ten years, 40 times more information has been obtained than was previously possible.
Then using trigonometric calculations the distance to a certain star is determined.
Distance to star clusters.
It is easier to calculate the distance to star clusters, especially open ones. The stars are located relatively close to each other, therefore, by calculating the distance to one star, you can determine the distance to the whole star cluster.
Additionally, in this case you can use statistical methods, allowing to reduce the number of inaccuracies. For example, the method of “converging points”, it is often used by astronomers. It is based on the fact that during long-term observation of stars in an open cluster, those moving towards a common point are identified, which is called a convergent point. By measuring the angles and radial velocities (that is, the speed of approaching and moving away from the Earth), you can determine the distance to the star cluster. Using this method there is a possible 15% inaccuracy at a distance of 1500 light years. It is also used at distances of 15,000 light years, which is quite suitable for celestial bodies in our Galaxy.
Main Sequence Fitting – establishment of the Main Sequence.
To determine the distance to distant star clusters, for example to the Pleiades, you can proceed as follows: build a G-R diagram, using vertical axis note the apparent magnitude (not absolute, since it depends on distance), which depends on temperature.
Then you should compare the resulting picture with the G-R Iad diagram, it has a lot common features in terms of Main Sequences. By combining the two diagrams as closely as possible, it is possible to determine the Main Sequence of the star cluster whose distance must be measured.
Then the equation should be used:
m-M=5log(d)-5, where
m – apparent magnitude;
M – absolute magnitude;
d – distance.
In English this method is called “Main Sequence Fitting”. It can be used for open star clusters such as NGC 2362, Alpha Persei, III Cephei, NGC 6611. Astronomers have attempted to determine the distance to the famous double open star cluster in the constellation Perseus ("h" and "chi"), where many stars are located -supergiants. But the data turned out to be contradictory. Using the “Main Sequence Fitting” method, it is possible to determine distances up to 20,000-25,000 light years, this is a fifth of our Galaxy.
Light intensity and distance.
The further away a celestial body is, the weaker its light appears. This position is consistent with the optical law, according to which the intensity of light "I" is inversely proportional to the distance squared "d".
For example, if one galaxy is located at a distance of 10 million light years, then another galaxy located 20 million light years away has a brightness four times smaller than the first. That is, from a mathematical point of view, the relationship between the two quantities “I” and “d” is precise and measurable. In the language of astrophysics, the intensity of light is the absolute magnitude of the stellar magnitude M of some celestial object, the distance to which should be measured.
Using the equation m-M=5log(d)-5 (it reflects the law of change in brightness) and knowing that m can always be determined using a photometer, and M is known, the distance “d” is measured. So, knowing the absolute magnitude, using calculations it is not difficult to determine the distance.
Interstellar absorption.
One of the main problems associated with distance measuring methods is the problem of light absorption. On its way to Earth, light travels vast distances, passing through interstellar dust and gas. Accordingly, part of the light is adsorbed, and when it reaches telescopes installed on Earth, it already has a non-original strength. Scientists call this “extinction,” the weakening of light. It is very important to calculate the amount of extinction when using a number of methods, such as candela. In this case, the exact absolute magnitudes must be known.
It is not difficult to determine the extinction for our Galaxy - just take into account dust and gas Milky Way. It is more difficult to determine the extinction of light from an object in another galaxy. To the extinction along the path in our Galaxy, we must also add part of the absorbed light from another.
EVOLUTION OF STARS.
The internal life of a star is regulated by the influence of two forces: the force of gravity, which counteracts the star and holds it, and the force released during nuclear reactions occurring in the core. On the contrary, it tends to “push” the star into distant space. During the formation stage, a dense and compressed star is under strong impact gravity. As a result, strong heating occurs, the temperature reaches 10-20 million degrees. This is enough to start nuclear reactions, as a result of which hydrogen is converted into helium.
Then, over a long period, the two forces balance each other, the star is in a stable state. When the nuclear fuel in the core gradually runs out, the star enters an instability phase, two forces opposing each other. A critical moment comes for the star, the most various factors– temperature, density, chemical composition. The mass of the star comes first; the future of this celestial body depends on it - either the star will explode like a supernova, or turn into a white dwarf, a neutron star or a black hole.
How does hydrogen run out?
Only the very largest among celestial bodies become stars, the smaller ones become planets. There are also bodies average weight, they are too large to belong to the class of planets, and too small and cold for nuclear reactions characteristic of stars to occur in their depths.
So, a star is formed from clouds of interstellar gas. As already noted, the star remains in a balanced state for quite a long time. Then comes a period of instability. The further fate of the star depends on various factors. Consider a hypothetical small star whose mass is between 0.1 and 4 solar masses. A characteristic feature of stars with low mass is the absence of convection in the inner layers, i.e. The substances that make up the star do not mix, as happens in stars with a large mass.
This means that when the hydrogen in the core runs out, there are no new reserves of this element in the outer layers. Hydrogen burns and turns into helium. Little by little the core heats up, the surface layers destabilize their own structure, and the star, as can be seen from the H-R diagram, slowly leaves the Main Sequence. In the new phase, the density of matter inside the star increases, the composition of the core “degenerates”, and as a result a special consistency appears. It is different from normal matter.
Modification of matter.
When matter changes, pressure depends only on the density of the gases, not on temperature.
In the Hertzsprung-Russell diagram, the star moves to the right and then upward, approaching the red giant region. Its dimensions increase significantly, and because of this, the temperature of the outer layers drops. The diameter of a red giant can reach hundreds of millions of kilometers. When our sun enters this phase, it will “swallow” both Mercury and Venus, and if it cannot capture the Earth, it will heat it up to such an extent that life on our planet will cease to exist.
During the evolution of a star, the temperature of its core increases. First, nuclear reactions occur, then, upon reaching the optimal temperature, helium begins to melt. When this happens, a sudden increase in core temperature causes a flare and the star quickly moves into left side G-R diagrams. This is the so-called “helium flash”. At this time, the core containing helium burns together with hydrogen, which is part of the shell surrounding the core. On the H-R diagram, this stage is recorded by moving to the right along a horizontal line.
The last phases of evolution.
When helium is transformed into a hydrocarbon, the core is modified. Its temperature rises until the carbon begins to burn. A new outbreak occurs. In any case, during the last phases of the star’s evolution, a significant loss of its mass is noted. This can happen gradually or abruptly, during an outburst, when the outer layers of the star burst as big bubble. IN the latter case a planetary nebula is formed - a spherical shell spreading into outer space at a speed of several tens or even hundreds of km/sec.
The final fate of a star depends on the mass remaining after everything that happens to it. If during all transformations and flares it ejected a lot of matter and its mass does not exceed 1.44 solar masses, the star turns into a white dwarf. This one is called the “Chandrasekhar limit” after the Pakistani astrophysicist Subrahmanyan Chandrasekhar. This is the maximum mass of a star at which a catastrophic end may not occur due to the pressure of electrons in the core.
After the outbreak of the outer layers, the core of the star remains, and its surface temperature is very high - about 100,000 o K. The star moves to the left edge of the H-R diagram and goes down. Its luminosity decreases as its size decreases.
The star is slowly reaching the white dwarf zone. These are stars of small diameter, but very high density, one and a half million times the density of water.
A white dwarf represents the final stage of star evolution, without outbursts. She is gradually cooling down. Scientists believe that the end of the white dwarf is very slow, at least since the beginning of the Universe, it seems that not a single white dwarf has suffered from “thermal death”.
If the star is large and its mass is greater than the Sun, it will explode like a supernova. During a flare, a star may collapse completely or partially. In the first case, what will be left behind is a cloud of gas with residual substances of the star. In the second, a celestial body of the highest density will remain - a neutron star or a black hole.
VARIABLE STARS.
According to Aristotle's concept, the celestial bodies of the Universe are eternal and permanent. But this theory underwent significant changes with the appearance in the 17th century. the first binoculars. Observations carried out over subsequent centuries demonstrated that, in fact, the apparent constancy of celestial bodies is explained by the lack of observation technology or its imperfection. Scientists have concluded that variability is a common characteristic of all types of stars. During evolution, a star goes through several stages, during which its main characteristics - color and luminosity - undergo profound changes. They occur during the existence of a star, which is tens or hundreds of millions of years, so a person cannot be an eyewitness to what is happening. For some classes of stars, changes occurring are recorded in short periods of time, for example, over several months, days or part of a day. The star's changes and its luminous fluxes can be measured many times over subsequent nights.
Measurements.
In fact, this problem is not as simple as it seems at first glance. When carrying out measurements, it is necessary to take into account atmospheric conditions, and they change, sometimes significantly within one night. In this regard, data on the luminous fluxes of stars vary significantly.
It is very important to be able to distinguish real changes in the light flux, and they are directly related to the brightness of the star, from apparent ones, which are explained by changes in atmospheric conditions.
To do this, it is recommended to compare the light fluxes of the observed star with other stars - landmarks visible through a telescope. If the changes are apparent, i.e. associated with changes in atmospheric conditions, they affect all observed stars.
Obtaining correct data about the state of the star at some stage is the first step. Next, you should create a “light curve” to capture possible changes shine. It will show the change in magnitude.
Variables or not.
Stars whose magnitude is not constant are called variables. For some of them, variability is only apparent. These are mainly stars belonging to the binary system. Moreover, when the orbital plane of the system more or less coincides with the observer’s line of sight, it may seem to him that one of the two stars is completely or partially eclipsed by the other and is less bright. In these cases, the changes are periodic, periods of change in brightness eclipsing stars repeat at intervals that coincide with the orbital period of the binary star system. These stars are called "eclipsing variables."
Next class variable stars– “internal variables”. The amplitudes of the brightness fluctuations of these stars depend on the physical parameters of the star, such as radius and temperature. For many years, astronomers have been observing the variability of variable stars. In our Galaxy alone, 30,000 variable stars have been recorded. They were divided into two groups. The first category includes “eruptive variable stars.” They are characterized by single or repeated outbreaks. Changes in stellar magnitudes are episodic. The class of “eruptive variables,” or explosive ones, also includes novae and supernovae. The second group includes everyone else.
Cepheids.
There are variable stars whose brightness changes strictly periodically. Changes occur at certain intervals. If you draw a light curve, it will clearly record the regularity of changes, while the shape of the curve will mark the maximum and minimum characteristics. The difference between the maximum and minimum fluctuations defines a large space between the two characteristics. Stars of this type are classified as “pulsating variables.” From the light curve we can conclude that the star's brightness increases faster than it decreases.
Variable stars are divided into classes. The prototype star is taken as a criterion; it is this star that gives the name to the class. An example is the Cepheids. This name comes from the star Cepheus. This is the simplest criterion. There is another one - stars are divided according to their spectra.
Variable stars can be divided into subgroups according to different criteria.
DOUBLE STARS.
Stars in the firmament exist in the form of clusters, associations, and not as individual bodies. Star clusters can be very densely populated with stars or not.
Closer connections can exist between stars; we are talking about binary systems, as astronomers call them. In a pair of stars, the evolution of one directly affects the second.
Opening.
The discovery of double stars, as they are now called, was one of the first discoveries made using astronomical binoculars. The first pair of this type of stars was Mizar from the constellation Ursa Major. The discovery was made by the Italian astronomer Riccioli. Considering the huge number of stars in the Universe, scientists came to the conclusion that Mizar was not the only binary system among them, and they were right; observations soon confirmed this hypothesis. In 1804, the famous astronomer William Herschel, who devoted 24 years of scientific observations, published a catalog containing descriptions of approximately 700 double stars. At first, scientists did not know for sure whether the components of the binary system were physically connected to each other.
Some bright minds believed that double stars were affected by the stellar association as a whole, especially since the brightness of the components in the pair was not the same. In this regard, it seemed that they were not nearby. To determine the true position of the bodies, it was necessary to measure the parallactic displacements of the stars. This is what Herschel did. To the greatest surprise, the parallactic displacement of one star relative to another during the measurement gave an unexpected result. Herschel noticed that instead of oscillating symmetrically with a period of 6 months, each star followed a complex ellipsoidal path. In accordance with the laws of celestial mechanics, two bodies connected by gravity move in an elliptical orbit. Herschel's observations confirmed the thesis that double stars are connected physically, that is, by gravitational forces.
Classification of double stars.
There are three main classes of double stars: visual binaries, photometric binaries, and spectroscopic binaries. This classification does not fully reflect the internal differences between the classes, but gives an idea of the stellar association.
The duality of visual double stars is clearly visible through a telescope as they move. Currently, about 70,000 visual binaries have been identified, but only 1% of them have had an accurately determined orbit.
This figure (1%) should not be surprising. The fact is that orbital periods can be several decades, if not entire centuries. And building a path along the orbit is a very painstaking work, requiring numerous calculations and observations from different observatories. Very often, scientists have only fragments of the orbital movement; they reconstruct the rest of the path deductively, using the available data. It should be borne in mind that the orbital plane of the system may be inclined to the line of sight. In this case, the reconstructed orbit (apparent) will differ significantly from the true one.
If the true orbit is determined, the period of revolution and the angular distance between the two stars are known, it is possible, by applying Kepler's third law, to determine the sum of the masses of the system components. The distance of the double star to us should also be known.
Double photometric stars.
The duality of this system of stars can be judged only by periodic fluctuations in brightness. When moving, such stars alternately block each other. They are also called "eclipsing double stars." These stars have orbital planes close to the direction of the line of sight. How large area occupies an eclipse, the more pronounced the brilliance. If you analyze the light curve of double photometric stars, you can determine the inclination of the orbital plane.
Using the light curve, you can also determine the orbital period of the system. If, for example, two eclipses are recorded, the light curve will have two decreases (minimum). The time period during which three successive decreases along the light curve are recorded corresponds to the orbital period.
The periods of photometric binary stars are much shorter compared to the periods of visual binary stars and last for several hours or several days.
Spectral dual stars.
Using spectroscopy, one can notice the splitting of spectral lines due to the Doppler effect. If one of the components is a faint star, then only periodic oscillation positions of single lines. This method is used when the components of a double star are very close to each other and are difficult to identify with a telescope as visual double stars. Binary stars determined using a spectroscope and the Doppler effect are called spectral binaries. Not all double stars are spectral. The two components of binary stars can move away and approach in a radial direction.
Observations indicate that double stars are found mainly in our Galaxy. It is difficult to determine the percentage of double and single stars. If we use the subtraction method and subtract the number of identified double stars from the entire stellar population, we can conclude that they constitute a minority. This conclusion may be erroneous. In astronomy there is the concept of “selection effect”. To determine the binarity of stars, it is necessary to identify their main characteristics. This requires good equipment. Binary stars can sometimes be difficult to identify. For example, visual double stars cannot always be seen on great distance from the observer. Sometimes the angular distance between components is not recorded by the telescope. In order to detect photometric and spectroscopic binaries, their brightness must be strong enough to collect modulations of the light flux and carefully measure the wavelengths in spectral lines.
The number of stars suitable in all respects for research is not so large. According to theoretical developments, it can be assumed that double stars make up from 30% to 70% of the stellar population.
NEW STARS.
Variable explosive stars consist of a white dwarf and a Main Sequence star, like the Sun, or a post-sequence star, like a red giant. Both stars follow a narrow orbit every few hours. They are on close range from each other, due to which they closely interact and cause spectacular phenomena.
Since the middle of the 19th century, scientists have recorded the predominance of purple at certain times, this phenomenon coincides with the presence of peaks in the light curve. Based on this principle, the stars were divided into several groups.
Classic novae.
Classical novae differ from explosive variables in that their optical outbursts do not have a repeating character. The amplitude of their light curve is more clearly expressed, and the rise to maximum point happens much faster. They usually reach maximum brightness in a few hours, during which time the new star acquires a magnitude of approximately 12, that is, the luminous flux increases by 60,000 units.
The slower the process of rising to maximum, the less noticeable the change in brightness. The nova does not remain at its maximum position for long; this period usually lasts from several days to several months. The shine then begins to decrease, quickly at first, then more slowly to normal levels. The duration of this phase depends on various circumstances, but its duration is at least several years.
In new classical stars, all these phenomena are accompanied by uncontrolled thermonuclear reactions occurring in the surface layers of the white dwarf, which is where the “borrowed” hydrogen from the second component of the star is located. New stars are always binary, one of the components is necessarily a white dwarf. When the mass of the star component flows to the white dwarf, the hydrogen layer begins to compress and heats up, accordingly the temperature rises, and the helium heats up. All this happens quickly, sharply, resulting in an outbreak. The emitting surface increases, the star's brightness becomes bright, and a burst is recorded in the light curve.
During active phase During the outburst, the nova reaches its maximum brightness. The maximum absolute magnitude is on the order of -6 to -9. in new stars this figure is reached more slowly, in variable explosive stars it is achieved faster.
New stars also exist in other galaxies. But what we observe is only their apparent magnitude; the absolute magnitude cannot be determined, since their exact distance to the Earth is unknown. Although, in principle, it is possible to find out the absolute magnitude of a nova if it is in maximum proximity to another nova, the distance to which is known. The maximum absolute value is calculated using the equation:
M=-10.9+2.3log (t).
t is the time during which the light curve of the nova drops to 3 magnitudes.
Dwarf novae and repeating novae.
Immediate relatives novae are dwarf novae, their prototype "U Gemini". Their optical flares are almost similar to the flares of new stars, but there are differences in the light curves: their amplitudes are smaller. Differences are also noted in the frequency of outbreaks - in new dwarf stars they happen more or less regularly. On average once every 120 days, but sometimes every few years. The optical flashes of the novae last from several hours to several days, after which the brightness decreases over several weeks and finally reaches normal levels.
The existing difference can be explained by different physical mechanisms that provoke the optical flash. In Gemini U, flares occur due to a sudden change in the percentage of matter on the white dwarf - an increase in it. The result is a huge release of energy. Observations of dwarf novae during the eclipse phase, that is, when the white dwarf and the disk surrounding it are obscured by a component star of the system, clearly indicate that it is the white dwarf, or rather its disk, that is the source of light.
Recurring novae are a cross between classical novae and dwarf novae. As the name suggests, their optical flares repeat regularly, which makes them similar to new dwarf stars, but this happens after several decades. The increase in brightness during a flare is more pronounced and amounts to about 8 magnitudes; this feature brings them closer to classical novae.
OPEN STAR CLUSTERS.
Open star clusters are not difficult to find. They are called galaxy clusters. We are talking about formations that include from several tens to several thousand stars, most of which is visible to the naked eye. Star clusters appear to the observer as a section of the sky densely dotted with stars. As a rule, such areas of concentration of stars are clearly visible in the sky, but it happens, quite rarely, that the cluster is practically indistinguishable. In order to determine whether any part of the sky is a star cluster or whether we are talking about stars simply located close to each other, one should study their movement and determine the distance to the Earth. The stars that make up the clusters move in the same direction. In addition, if stars that are not far from each other are located at the same distance from the solar system, they are, of course, connected to each other by gravitational forces and form an open cluster.
Classification of star clusters.
The extent of these star systems varies from 6 to 30 light years, with an average extent of approximately twelve light years. Inside star clusters, stars are concentrated chaotically, unsystematically. The cluster does not have a clearly defined shape. When classifying star clusters, one must take into account angular measurements, the approximate total number of stars, their degree of concentration in the cluster, and differences in brightness.
In 1930, American astronomer Robert Trumpler proposed classifying clusters according to the following parameters. All clusters were divided into four classes based on the concentration of stars and were designated by Roman numerals from I to IV. Each of the four classes is divided into three subclasses based on the uniformity of stellar brightness. The first subclass includes clusters in which the stars have approximately the same degree of luminosity, the third - with a significant difference in this regard. Then the American astronomer introduced three more categories for classifying star clusters according to the number of stars included in the cluster. The first category “p” includes systems with less than 50 stars. The second “m” is a cluster with from 50 to 100 stars. The third - those with more than 100 stars. For example, according to this classification, a star cluster identified in the catalog as “I 3p” is a system consisting of fewer than 50 stars, densely concentrated in the sky and having varying degrees of brightness.
Uniformity of stars.
All stars belonging to any open star cluster have characteristic feature– homogeneity. This means that they were formed from the same gas cloud and at first they had the same chemical composition. In addition, there is an assumption that they all appeared at the same time, that is, they are the same age. The differences between them can be explained by the different course of development, and this is determined by the mass of the star from the moment of its formation. Scientists know that large stars have a shorter lifespan compared to small stars. Large ones evolve much faster. In general, open star clusters are celestial systems consisting of relatively young stars. This type of star clusters is located mainly in the spiral arms of the Milky Way. These areas were active star formation zones in the recent past. The exceptions are the clusters NGC 2244, NGC 2264 and NGC6530, their age is several tens of millions of years. This is a short time for the stars.
Age and chemical composition.
Stars in open star clusters are connected by gravity. But because this connection is not strong enough, open clusters can disintegrate. This happens over a long period of time. The dissolution process is associated with the influence of gravity from single stars located near the cluster.
There are practically no old stars in open star clusters. Although there are exceptions. This primarily applies to large clusters, in which the connection between stars is much stronger. Accordingly, the age of such systems is greater. Among them is NGC 6791. This star cluster includes approximately 10,000 stars and is about 10 billion years old. The orbits of large star clusters take them far from the galactic plane for long periods of time. Accordingly, they have less opportunity to encounter large molecular clouds, which could lead to the dissolution of the star cluster.
Stars in open star clusters are similar in chemical composition to the Sun and other stars in the galactic disk. The difference in chemical composition depends on the distance from the center of the Galaxy. The farther from the center a star cluster is located, the fewer elements from the metal group it contains. The chemical composition also depends on the age of the star cluster. This also applies to single stars.
Globular star clusters.
Globular star clusters, numbering hundreds of thousands of stars, have a very unusual appearance: they have a spherical shape, and the stars are concentrated in them so densely that even with the help of the most powerful telescopes it is impossible to distinguish single objects. There is a strong concentration of stars towards the center.
Research on globular clusters is important in astrophysics in terms of studying the evolution of stars, the process of galaxy formation, studying the structure of our Galaxy and determining the age of the Universe.
The shape of the Milky Way.
Scientists have found that globular clusters formed at the initial stage of the formation of our Galaxy - the protogalactic gas had a spherical shape. During the gravitational interaction until the compression was completed, which led to the formation of the disk, clumps of matter, gas and dust appeared outside of it. It is from them that globular star clusters were formed. Moreover, they were formed before the appearance of the disk and remained in the same place where they were formed. They have a spherical structure, a halo, around which the plane of the galaxy was later located. This is why globular clusters are distributed symmetrically in the Milky Way.
The study of the problem of the location of globular clusters, as well as measurements of the distance from them to the Sun, made it possible to determine their extent of our Galaxy to the center - it is 30,000 light years.
Globular star clusters are very old in terms of their time of origin. Their age is 10-20 billion years. They represent the most important element of the Universe, and, undoubtedly, knowledge about these formations will provide considerable assistance in explaining the phenomena of the Universe. According to scientists, the age of these star clusters is identical to the age of our Galaxy, and since all galaxies were formed at approximately the same time, it means that the age of the Universe can be determined. To do this, the time from the appearance of the Universe to the beginning of the formation of galaxies should be added to the age of globular star clusters. Compared to the age of globular star clusters, this is quite small segment time.
Inside the cores of globular clusters.
The central regions of this type of cluster are characterized by a high degree of concentration of stars, approximately thousands of times more than in the zones closest to the Sun. Only over the last decade has it become possible to examine the cores of globular star clusters, or rather, those celestial objects that are located in the very center. This is of great importance in the field of studying the dynamics of stars included in the core, in terms of obtaining information about systems of celestial bodies connected by gravitational forces - star clusters belong precisely to this category - as well as in terms of studying the interaction between stars of clusters through observations or data processing on the computer.
Due to the high degree of concentration of stars, real collisions occur and new objects are formed, for example stars, which have their own characteristics. Binary systems can also appear; this happens when the collision of two stars does not lead to their destruction, but mutual capture occurs due to gravity.
Families of globular star clusters.
Globular star clusters of our Galaxy are heterogeneous formations. Four dynamic families are distinguished according to the principle of distance from the center of the Galaxy and according to their chemical composition. Some globular clusters have more metal group chemical elements, others have less. The degree of presence of metals depends on the chemical composition of the interstellar medium from which celestial objects were formed. Globular clusters with fewer metals are older and are located in the halo of the Galaxy. A higher metal composition is characteristic of younger stars, they were formed from an environment already enriched in metals due to supernova explosions - this family includes “disk clusters” found on the galactic disk.
The halo contains "halo-inner star clusters" and "halo-outer star clusters." There are also “star clusters of the peripheral part of the halo”, the distance from which to the center of the Galaxy is greatest.
Environmental influence.
Star clusters are not studied and divided into families for the sake of classification as an end in themselves. Classification also plays an important role in studying the influence of the environment surrounding a star cluster on its evolution. In this case we are talking about our Galaxy.
Undoubtedly, the star cluster is greatly influenced by the gravitational field of the Galaxy's disk. Globular star clusters move around the galactic center in elliptical orbits and periodically cross the galactic disk. This happens once every 100 million years.
The gravitational field and tidal projections emanating from the galactic plane act so intensely on the star cluster that it gradually begins to disintegrate. Scientists believe that some old stars currently located in the Galaxy were once part of globular star clusters. Now they have already collapsed. It is believed that approximately 5 star clusters disintegrate every billion years. This is an example of the influence of the galactic environment on the dynamic evolution of a globular star cluster.
Under the influence gravitational influence As the galactic disk permeates the star cluster, the extent of the cluster also changes. We are talking about stars located far from the center of the cluster; they are influenced to a greater extent by the gravitational force of the galactic disk, and not by the star cluster itself. Stars “evaporate” and the size of the cluster decreases.
SUPERNOVA STARS.
Stars are also born, grow and die. Their end may be slow and gradual or abrupt and catastrophic. This is typical for very large stars that end their existence with an outburst; these are supernovae.
Discovery of supernovae.
For centuries, the nature of supernovae was unknown to scientists, but observations of them have been carried out since time immemorial. Many supernovae are so bright that they can be seen with the naked eye, sometimes even during the day. The first mentions of these stars appeared in ancient chronicles in 185 AD. Subsequently, they were observed regularly and all data was scrupulously recorded. For example, the court astronomers of the emperors of ancient China recorded many of the discovered supernovae many years later.
Notable among them is the supernova that erupted in 1054 AD. in the constellation Taurus. The remnant of this supernova is called the Crab Nebula because of its characteristic shape. Systematic observations of supernovas Western astronomers began to lead late. Only towards the end of the 16th century. references to them appeared in scientific documents. The first observations of supernovae by European astronomers date back to 1575 and 1604. In 1885, the first supernova was discovered in the Andromeda galaxy. This was done by Baroness Bertha de Podmanicka.
Since the 20s of the XX century. Thanks to the invention of photographic plates, supernova discoveries follow one after another. Currently, there are up to a thousand of them open. Finding supernovae requires a lot of patience and constant monitoring behind the sky. The star must not only be very bright, its behavior must be unusual and unpredictable. There are not so many “supernova hunters”; a little more than ten astronomers can boast that they have discovered more than 20 supernovae in their lifetime. The leader in this interesting classification belongs to Fred Zwicky - since 1936, he has identified 123 stars.
What are supernovae?
Supernovae are stars that explode suddenly. This flare is a catastrophic event, the end of the evolution of large stars. During flares, the radiation power reaches 1051 erg, which is comparable to the energy emitted by the star throughout its entire life. The mechanisms that cause flares in double and single stars are different.
In the first case, the outburst occurs under the condition that the second star in the binary system is a white dwarf. White dwarfs are relatively small stars, their mass corresponds to the mass of the Sun, in the end " life path"They are the size of a planet. The white dwarf interacts with its pair in a gravitational way; it “steals” matter from its surface layers. The “borrowed” substance heats up, nuclear reactions begin, and an outbreak occurs.
In the second case, the star itself flares up; this happens when there are no longer conditions for thermonuclear reactions. At this stage, gravity dominates and the star begins to contract at a rapid rate. Due to sudden heating as a result of compression, uncontrolled nuclear reactions begin to occur in the star's core, energy is released in the form of a flash, causing the destruction of the star.
After the flash, a cloud of gas remains and spreads in space. These are “supernova remnants” - what remains from the surface layers of an exploding star. The morphology of supernova remnants is different and depends on the conditions in which the explosion of the “progenitor” star occurred, and on its characteristic internal features. The cloud spreads unequally in different directions, which is due to interaction with interstellar gas, which can significantly change the shape of the cloud over thousands of years.
Characteristics of supernovae.
Supernovae are a variation of eruptive variable stars. Like all variables, supernovae are characterized by a light curve and easily recognizable features. First of all, a supernova is characterized by a rapid increase in brightness, it lasts several days until it reaches a maximum - this period is approximately ten days. Then the shine begins to decrease - first haphazardly, then consistently. By studying the light curve, you can trace the dynamics of the flare and study its evolution. The part of the light curve from the beginning of the rise to the maximum corresponds to the outburst of the star, the subsequent descent means expansion and cooling gas shell.
WHITE Dwarfs.
In the “star zoo” there are a great variety of stars, different in size, color and brilliance. Among them, “dead” stars are especially impressive; their internal structure differs significantly from the structure of ordinary stars. The category of dead stars includes large stars, white dwarfs, neutron stars and black holes. Due to the high density of these stars, they are classified as “crisis” stars.
Opening.
At first, the essence of white dwarfs was a complete mystery; all that was known was that they had a high density compared to ordinary stars.
The first white dwarf to be discovered and studied was Sirius B, a pair of Sirius, a very bright star. Using Kepler's third law, astronomers calculated the mass of Sirius B: 0.75-0.95 solar masses. On the other hand, its brightness was significantly lower than that of the sun. The brightness of a star is related to the square of its radius. After analyzing the numbers, astronomers came to the conclusion that the size of Sirius is small. In 1914, the stellar spectrum of Sirius B was compiled and the temperature was determined. Knowing the temperature and brightness, we calculated the radius - 18,800 kilometers.
First research.
The obtained result marked the discovery of a new class of stars. In 1925, Adams measured the wavelength of some emission lines in the spectrum of Sirius B and determined that they were longer than expected. The red shift fits into the framework of the theory of relativity, discovered by Einstein several years before the events taking place. Using the theory of relativity, Adams was able to calculate the radius of the star. After the discovery of two more stars similar to Sirius B, Arthur Eddington concluded that there are many such stars in the Universe.
So, the existence of dwarfs was established, but their nature still remained a mystery. In particular, scientists could not understand how a mass similar to the sun could fit in such a small body. Eddington concludes that “at such a high density the gas loses its properties. Most likely, white dwarfs consist of degenerate gas."
The essence of white dwarfs.
In August 1926, Enrico Fermi and Paul Dirac developed a theory describing the state of gas under conditions of very high density. Using it, Fowler in the same year found an explanation for the stable structure of white dwarfs. In his opinion, due to high density, the gas in the interior of the white dwarf is in a degenerate state, and the gas pressure is practically independent of temperature. The stability of a white dwarf is maintained by the fact that the force of gravity is opposed by the gas pressure in the bowels of the dwarf. The study of white dwarfs was continued by the Indian physicist Chandrasekhar.
In one of his works, published in 1931, he does important discovery– the mass of white dwarfs cannot exceed a certain limit, this is due to their chemical composition. This limit is 1.4 solar masses and is called the “Chandrasekhar limit” in honor of the scientist.
Almost a ton per cm3!
As their name suggests, white dwarfs are small stars. Even if their mass is equal to the mass of the Sun, they are still similar in size to a planet like Earth. Their radius is approximately 6000 km - 1/100 of the radius of the Sun. Considering the mass of white dwarfs and their size, only one conclusion can be drawn - their density is very high. A cubic centimeter of white dwarf matter weighs almost a ton by Earth standards.
Such a high density leads to the fact that the gravitational field of the star is very strong - about 100 times higher than the solar one, and with the same mass.
Main characteristics.
Although the core of white dwarfs no longer undergoes nuclear reactions, its temperature is very high. Heat rushes to the surface of the star and then spreads out into space. The stars themselves slowly cool down until they become invisible. The surface temperature of “young” white dwarfs is about 20,000-30,000 degrees. White dwarfs are not only white, there are also yellow ones. Despite the high surface temperature, due to small sizes The luminosity is low, the absolute magnitude can be 12-16. White dwarfs cool very slowly, which is why we see them in such large numbers. Scientists have the opportunity to study their main characteristics. White dwarfs are included in the H-R diagram and occupy a small space below the Main Sequence.
NEUTRON STARS AND PULSARS.
The name "pulsar" comes from the English combination "pulsating star" - "pulsating star". A characteristic feature of pulsars, unlike other stars, is not constant radiation, but regular pulsed radio emission. The pulses are very fast, the duration of one pulse lasts from thousandths of a second to, at most, several seconds. The pulse shape and periods are different for different pulsars. Due to the strict periodicity of radio emission, pulsars can be considered as cosmic chronometers. Over time, the periods decrease to 10-14 s/s. Every second the period changes by 10-14 seconds, that is, the decrease occurs over about 3 million years.
Regular signals.
The history of the discovery of pulsars is quite interesting. The first pulsar, PSR 1919+21, was detected in 1967 by Bell and Anthony Huish of Cambridge University. Bell, a young physicist, conducted research in the field of radio astronomy to confirm the theses he put forward. Suddenly he discovered a radio signal of moderate intensity in an area close to the galactic plane. The strange thing was that the signal was intermittent - it disappeared and reappeared at regular intervals of 1.377 seconds. They say that Bell ran to his professor to notify him of the discovery, but the latter did not pay due attention to this, believing that it was a radio signal from the Earth.
Nevertheless, the signal continued to appear regardless of terrestrial radioactivity. This indicated that the source of its appearance had not yet been established. As soon as the data about the discovery were published, numerous speculations arose that the signals were coming from a ghostly extraterrestrial civilization. But scientists were able to understand the essence of pulsars without the help of alien worlds.
The essence of pulsars.
After the first one, many more pulsars were discovered. Astronomers have concluded that these celestial bodies are sources of pulsed radiation. The most numerous objects in the Universe are stars, so scientists decided that these celestial bodies most likely belong to the class of stars.
Fast movement the stars around their axis is most likely the cause of the pulsations. Scientists measured the periods and tried to determine the essence of these celestial bodies. If a body rotates at a speed exceeding a certain maximum speed, it disintegrates under the influence of centrifugal forces. This means that there must be a minimum value of the rotation period.
From the calculations performed, it followed that for a star to rotate with a period measured in thousandths of a second, its density should be on the order of 1014 g/cm3, like that of atomic nuclei. For clarity, we can give the following example: imagine a mass equal to Everest in the volume of a piece of sugar.
Neutron stars.
Since the thirties, scientists have assumed that something similar exists in the sky. Neutron stars are very small, super-dense celestial bodies. Their mass is approximately equal to 1.5 solar masses, concentrated in a radius of approximately 10 km.
Neutron stars are made primarily of neutrons, particles without electric charge, which together with protons make up the nucleus of an atom. Because of high temperature in the interior of a star, matter is ionized, electrons exist separately from the nuclei. At such a high density, all nuclei decay into their constituent neutrons and protons. Neutron stars are the end result of the evolution of a large mass star. After exhausting the sources of thermonuclear energy in its depths, it explodes sharply, like a supernova. The outer layers of the star are thrown into space, gravitational collapse occurs in the core, and a hot neutron star is formed. The collapse process takes a fraction of a second. As a result of the collapse, it begins to rotate very quickly, with periods of thousandths of a second, which is typical for a pulsar.
Radiation of pulsations.
There are no sources of thermonuclear reactions in a neutron star, i.e. they are inactive. The emission of pulsations does not come from the interior of the star, but from the outside, from zones surrounding the surface of the star.
The magnetic field of neutron stars is very strong, millions of times greater than the magnetic field of the Sun, it cuts through space, creating a magnetosphere.
A neutron star emits streams of electrons and positrons into the magnetosphere; they rotate at speeds close to the speed of light. The magnetic field influences the movement of these elementary particles; they move along power lines, following a spiral trajectory. Thus, they release kinetic energy in the form of electromagnetic radiation.
The rotation period increases due to the decrease in rotational energy. Older pulsars have a longer pulsation period. By the way, the pulsation period is not always strictly periodic. Sometimes it slows down sharply, this is associated with phenomena called “glitches” - this is the result of “microstarquakes”.
BLACK HOLES.
The image of the firmament amazes with the variety of shapes and colors of celestial bodies. What is there in the Universe: stars of all colors and sizes, spiral galaxies, nebulae unusual shapes and color schemes. But in this “cosmic zoo” there are “specimens” that excite special interest. These are even more mysterious celestial bodies, as they are difficult to observe. In addition, their nature is not fully understood. Among them special place belongs to "black holes".
Movement speed.
In everyday speech, the expression “black hole” means something bottomless, where a thing falls, and no one will ever know what happened to it in the future. What are black holes really? To understand this, let's go back in history two centuries ago. In the 18th century, the French mathematician Pierre Simon de Laplace first introduced this term while studying the theory of gravitation. As you know, any body that has a certain mass - the Earth, for example - also has a gravitational field; it attracts surrounding bodies.
This is why an object thrown up falls to the Earth. If the same object is thrown forward with force, it will overcome the gravity of the Earth for some time and fly some distance. Minimum required speed called “movement speed”, for the Earth it is 11 km/s. The speed of movement depends on the density of the celestial body, which creates a gravitational field. How higher density, the higher the speed should be. Accordingly, one can make the assumption, as Laplace did two centuries ago, that there are bodies in the Universe with such high density yu that the speed of their movement exceeds the speed of light, that is, 300,000 km/s.
In this case, even light could succumb to the gravitational force of such a body. Such a body could not emit light, and therefore it would remain invisible. We can imagine it as a huge hole, black in the picture. Undoubtedly, the theory formulated by Laplace does not bear the imprint of time and seems too simplified. However, at the time of Laplace it had not yet been formulated quantum theory, and from a conceptual point of view, considering light as a material body seemed nonsense. At the very beginning of the 20th century, with the emergence and development quantum mechanics It became known that light under certain conditions also acts as material radiation.
This position was developed in Albert Einstein's theory of relativity, published in 1915, and in the works German physicist Karl Schwarzschild in 1916, he provided a mathematical basis for the theory of black holes. Light can also be subject to gravity. Two centuries ago, Laplace raised a very important problem in terms of the development of physics as a science.
How do black holes appear?
The phenomena we are talking about received the name “black holes” in 1967 thanks to the American astrophysicist John Wheeler. They are the end result of the evolution of large stars whose mass is greater than five solar masses. When all nuclear fuel reserves are exhausted and reactions no longer occur, the death of the star occurs. Further, its fate depends on its mass.
If the mass of a star is less than the mass of the sun, it continues to contract until it goes out. If the mass is significant, the star explodes, then we are talking about supernova. The star leaves behind traces - when gravitational collapse occurs in the core, all the mass is collected into a ball of compact size with a very high density - 10,000 times more than that of the nucleus of an atom.
Relative effects.
For scientists, black holes are an excellent natural laboratory, allowing them to conduct experiments on various hypotheses in terms of theoretical physics. According to Einstein's theory of relativity, the laws of physics are influenced by a local gravitational field. In principle, time flows differently near gravitational fields of different intensities.
In addition, a black hole affects not only time, but also the surrounding space, affecting its structure. According to the theory of relativity, the presence of a strong gravitational field arising from such a powerful celestial body as a black hole distorts the structure of the surrounding space, and its geometric data changes. This means that about black hole a short distance connecting two points will not be a straight line, but a curve.
B the closest star to us is Sun. It is described in detail on a separate page. Here we will talk about stars in general, that is, including those that can be seen at night.
We will not exclude the Sun from the story either; on the contrary, we will always compare other stars with it. The distance to the Sun is 150,000,000 kilometers. This is 270,000 times closer than the closest star, excluding the Sun itself. It is clear why we know so much of what is known about the stars thanks to our daylight.
Even the light from nearest stars several years pass, and the stars themselves are at their most powerful telescopes visible as dots. However, this is not entirely true: stars are visible as tiny disks, but this is due to distortion in telescopes, and not to magnification. There are countless stars. No one can say exactly how many stars there are, especially since stars are born and die. We can only roughly state that there are about 150,000,000,000 stars in our Galaxy, and an unknown number of billions of galaxies in the Universe... But how many stars can be seen in the sky with the naked eye is known more precisely: about 4.5 thousand. Moreover, having set a certain limit for the brightness of stars, close in accessibility to the eye, we can name this number more precisely, almost down to unity. Bright stars have long been counted and cataloged. The brightness of a star (or, as they say, its brilliance) is characterized by its magnitude, which astronomers have long been able to determine. So what are stars?
Stars are hot balls of gas. The surface temperatures of stars vary. For some stars it can reach 30,000 K, while for others it can only be 3,000 K. Our Sun has a surface with a temperature of about 6,000 K. It must be noted that when we talk about the surface, we mean only the visible surface, since a gas ball cannot have any solid surface.
Normal stars are much more planets, But the main thing is much more massive. We will see that there are strange stars in the Universe that have sizes typical of planets, but are many times greater in mass than the latter. The Sun is 750 times more massive than all other bodies in the Solar System. You can learn more about the sizes of planets, asteroids and comets and about them themselves on the pages dedicated to the Solar System. There are stars that are hundreds of times larger in size than the Sun and the same number of times inferior to it in this indicator. However, the masses of stars vary within much more modest limits - from one twelfth of the mass of the Sun to 100 of its masses. Maybe there are heavier ones, but these massive stars very rare. It is not difficult to guess after reading the last lines that stars differ very much in density. Among them there are those whose cubic centimeter of substance outweighs a large loaded ocean ship. The matter of other stars is so discharged that its density is less than the density of the best vacuum that is achievable in earthly laboratory conditions. We will return to the conversation about the sizes, masses and densities of stars later.
|
|
|
|
|
|
Constellations are areas of the starry sky. To better navigate the starry sky, ancient people began to identify groups of stars that could be linked into individual figures, similar objects, mythological characters and animals. This system allowed people to organize the night sky, making each part of it easily recognizable. This simplified the study of celestial bodies, helped measure time, apply astronomical knowledge in agriculture and navigate by the stars. The stars that we see in our sky as if in one area can actually be extremely far from each other. In one constellation there may be stars that are in no way connected with each other, both very close and very far from the Earth.
There are 88 official constellations in total. In 1922, the International Astronomical Union officially recognized 88 constellations, 48 of which were described by the ancient Greek astronomer Ptolemy in his star catalog Almagest around 150 BC. There were gaps in Ptolemy's maps, especially southern sky. Which is quite logical - the constellations described by Ptolemy covered that part of the night sky that is visible from the south of Europe. The remaining gaps began to be filled during the times of great geographical discoveries. In the 14th century, the Dutch scientists Gerard Mercator, Pieter Keyser and Frederic de Houtman added new constellations to the existing list, and the Polish astronomer Jan Hevelius and the French Nicolas Louis de Lacaille completed what Ptolemy had started. On the territory of Russia, out of 88 constellations, about 54 can be observed. 
Knowledge about the constellations came to us from ancient cultures. Ptolemy compiled a map of the starry sky, but people used knowledge about the constellations long before that. At least in the 8th century BC, when Homer mentioned Bootes, Orion and the Big Dipper in his poems “Iliad” and “Odyssey”, people were already grouping the sky into separate figures. It is believed that the bulk of the knowledge of the ancient Greeks about the constellations came to them from the Egyptians, who, in turn, inherited it from the inhabitants of Ancient Babylon, Sumerians or Akkadians. About thirty constellations were already distinguished by the inhabitants of the Late Bronze Age, in 1650−1050. BC, judging by the records on clay tablets of Ancient Mesopotamia. References to constellations can also be found in Hebrew biblical texts. The most remarkable constellation, perhaps, is the constellation Orion: in almost every ancient culture it had its own name and was revered as special. So, in Ancient Egypt he was considered the incarnation of Osiris, and in Ancient Babylon called "The Faithful Shepherd of Heaven." But the most amazing discovery was made in 1972: a piece of Ivory a mammoth, more than 32 thousand years old, on which the constellation Orion was carved. 
We see different constellations depending on the time of year. Throughout the year, we see different parts of the sky (and different celestial bodies, respectively) because the Earth makes its annual voyage around the Sun. The constellations we see at night are those located behind the Earth on our side of the Sun, because... During the day, behind the bright rays of the Sun, we are unable to see them.
To better understand how this works, imagine that you are riding on a merry-go-round (this is the Earth) with a very bright, blinding light emanating from the center (the Sun). You will not be able to see what is in front of you because of the light, but you will only be able to discern what is outside the carousel. In this case, the picture will constantly change as you ride in a circle. Which constellations you observe in the sky and at what time of year they appear also depends on geographical latitude the beholder. 
Constellations travel from east to west, like the Sun. As soon as it begins to get dark, at dusk, the first constellations appear in the eastern part of the sky to pass across the entire sky and disappear with dawn in the western part. Due to the rotation of the Earth around its axis, it seems that the constellations, like the Sun, rise and set. The constellations we just observed on the western horizon just after sunset will soon disappear from our view, to be replaced by constellations that were higher up at sunset just a few weeks ago.
Constellations arising in the east have a diurnal shift of about 1 degree per day: completing a 360-degree trip around the Sun in 365 days gives about the same speed. Exactly one year later, at the same time, the stars will occupy exactly the same position in the sky. 
The movement of stars is an illusion and a matter of perspective. The direction in which stars move across the night sky is determined by the rotation of the Earth on its axis and really depends on the perspective and which way the viewer is facing.
Looking north, the constellations appear to move counterclockwise around a fixed point in the night sky, called north pole world located near the North Star. This perception is due to the fact that the earth rotates from west to east, i.e. the earth under your feet moves to the right, and the stars like the Sun, Moon and planets above your head follow the east-west direction, i.e. to the right left. However, if you face south, the stars will appear to move clockwise, from left to right. 
Zodiac constellations- these are those through which the Sun moves. The most famous constellations out of the 88 existing ones are the zodiacal ones. These include those through which the center of the Sun passes during the year. It is generally accepted that there are 12 zodiacal constellations in total, although in fact there are 13 of them: from November 30 to December 17, the Sun is in the constellation Ophiuchus, but astrologers do not classify it as a zodiac constellation. All zodiacal constellations are located along the visible annual path of the Sun among the stars, the ecliptic, at an inclination of 23.5 degrees to the equator. 
Some constellations have families are groups of constellations located in the same area of the night sky. As a rule, they assign names to the most significant constellation. The most “largely populated” constellation is Hercules, which has as many as 19 constellations. Other large families include Big Dipper(10 constellations), Perseus (9) and Orion (9). 
Celebrity constellations. The most big constellation- Hydra, it extends over more than 3% of the night sky, while the smallest in area, the Southern Cross, occupies only 0.165% of the sky. Centaurus boasts the largest number of visible stars, with 101 stars included in the famous constellation in the southern hemisphere of the sky. The constellation Canis Major includes the brightest star in our sky, Sirius, whose brilliance is −1.46m. But the constellation with the name Table Mountain is considered the dimmest and does not contain stars brighter than the 5th magnitude. Let us recall that in the numerical characteristic of the brightness of celestial bodies, the lower the value, the brighter the object (the brightness of the Sun, for example, is −26.7m). 
Asterism- this is not a constellation. An asterism is a group of stars with an established name, for example “ Big Dipper”, which is part of the constellation Ursa Major, or “Orion’s Belt” - three stars encircling the figure of Orion in the constellation of the same name. In other words, these are fragments of constellations that have secured a separate name for themselves. The term itself is not strictly scientific, but rather simply represents a tribute to tradition. 