On February 11, 2016, an international group of scientists, including from Russia, at a press conference in Washington announced a discovery that sooner or later will change the development of civilization. It was possible to prove in practice gravitational waves or waves of space-time. Their existence was predicted 100 years ago by Albert Einstein in his.
No one doubts that this discovery will be awarded the Nobel Prize. Scientists are in no hurry to talk about it practical application. But they remind us that until quite recently, humanity also did not know what to do with electromagnetic waves, which ultimately led to a real scientific and technological revolution.
What are gravitational waves in simple terms
Gravity and universal gravity- It is the same. Gravitational waves are one of the solutions to GPV. They must spread at the speed of light. It is emitted by any body moving with variable acceleration.
For example, it rotates in its orbit with variable acceleration directed towards the star. And this acceleration is constantly changing. The solar system emits energy on the order of several kilowatts in gravitational waves. This is an insignificant amount, comparable to 3 old color TVs.
Another thing is two pulsars (neutron stars) orbiting each other. They rotate very close orbits. Such a “couple” was discovered by astrophysicists and observed for a long time. The objects were ready to fall on each other, which indirectly indicated that pulsars emit space-time waves, that is, energy in their field.
Gravity is the force of gravity. We are drawn to the earth. And the essence of a gravitational wave is a change in this field, which is extremely weak when it reaches us. For example, take the water level in a reservoir. The gravitational field strength is the acceleration of free fall at a specific point. A wave runs across our pond, and suddenly the acceleration of free fall changes, just a little.
Such experiments began in the 60s of the last century. At that time, they came up with this: they hung a huge aluminum cylinder, cooled to avoid internal thermal fluctuations. And they waited for a wave from a collision, for example, of two massive black holes to suddenly reach us. The researchers were full of enthusiasm and said that the entire globe could be affected by a gravitational wave coming from outer space. The planet will begin to vibrate, and these seismic waves (compression, shear, and surface waves) can be studied.
An important article about the device in simple terms, and how the Americans and LIGO stole the idea of Soviet scientists and built introferometers that made the discovery possible. Nobody talks about it, everyone is silent!
By the way, gravitational radiation is more interesting from the position of cosmic microwave background radiation, which they are trying to find by changing the spectrum of electromagnetic radiation. CMB and electromagnetic radiation appeared 700 thousand years after the Big Bang, then during the expansion of the universe, filled with hot gas with running shock waves, which later turned into galaxies. In this case, naturally, a gigantic, mind-boggling number of space-time waves should have been emitted, affecting the wavelength of the cosmic microwave background radiation, which at that time was still optical. Russian astrophysicist Sazhin writes and regularly publishes articles on this topic.
Misinterpretation of the discovery of gravitational waves
“A mirror hangs, a gravitational wave acts on it, and it begins to oscillate. And even the most insignificant fluctuations with an amplitude less than the size of an atomic nucleus are noticed by instruments” - such an incorrect interpretation, for example, is used in the Wikipedia article. Don’t be lazy, find an article by Soviet scientists from 1962.
Firstly, the mirror must be massive in order to feel the “ripples”. Secondly, it needs to be cooled to almost absolute zero(in Kelvin) to avoid its own thermal fluctuations. Most likely, not only in the 21st century, but in general it will never be possible to detect elementary particle— carrier of gravitational waves:
“Recently, a series of long-term experiments on direct observation of gravitational waves aroused strong interest in the scientific community,” wrote a specialist in the field theoretical physics Michio Kaku in the book "Einstein's Cosmos" in 2004. — The LIGO project (“Laser Interferometer for Observing Gravitational Waves”) may be the first to “see” gravitational waves, most likely from the collision of two black holes in deep space. LIGO is a physicist's dream come true, the first facility with enough power to measure gravitational waves."
Kaku's prediction came true: on Thursday, a group of international scientists from the LIGO observatory announced the discovery of gravitational waves.
Gravitational waves are oscillations in space-time that "escape" massive objects (such as black holes) that are moving with acceleration. In other words, gravitational waves are a spreading disturbance of space-time, a traveling deformation of absolute emptiness.
A black hole is a region in space-time whose gravitational attraction is so strong that even objects moving at the speed of light (including light itself) cannot leave it. The boundary separating a black hole from the rest of the world is called the event horizon: everything that happens inside the event horizon is hidden from the eyes of an external observer.
Erin Ryan A photo of a cake posted online by Erin Ryan.
Scientists began catching gravitational waves half a century ago: it was then that the American physicist Joseph Weber became interested in Einstein’s general theory of relativity (GTR), took a sabbatical and began studying gravitational waves. Weber invented the first device to detect gravitational waves, and soon announced that he had recorded “the sound of gravitational waves.” However, science community denied his message.
However, it was thanks to Joseph Weber that many scientists turned into “wave chasers.” Today Weber is considered the father scientific direction gravitational wave astronomy.
"This is the beginning of a new era of gravitational astronomy"
The LIGO observatory, where scientists recorded gravitational waves, consists of three laser installations in the United States: two are located in Washington state and one in Louisiana. This is how Michio Kaku describes the operation of laser detectors: “The laser beam is split into two separate beams, which then go perpendicular to each other. Then, reflected from the mirror, they connect again. If through the interferometer ( measuring device) a gravitational wave will pass, the path lengths of the two laser beams will undergo a disturbance and this will be reflected in their interference pattern. To make sure that the signal recorded by the laser installation is not random, detectors should be placed at different points on the Earth.
Only under the influence of a gigantic gravitational wave, much larger than our planet in size, will all detectors operate simultaneously.”
Now the LIGO collaboration has detected gravitational radiation caused by the merger of a binary system of black holes with masses of 36 and 29 solar masses into an object with a mass of 62 solar masses. “This is the first direct (it is very important that it is direct!) measurement of the action of gravitational waves,” the professor commented to the correspondent of the Gazeta.Ru science department. Faculty of Physics Moscow State University Sergei Vyatchanin. — That is, a signal was received from the astrophysical catastrophe of the merger of two black holes. And this signal is identified - this is also very important! It is clear that this is from two black holes. And this is the beginning of a new era of gravitational astronomy, which will allow us to obtain information about the Universe not only through optical, X-ray, electromagnetic and neutrino sources - but also through gravitational waves.
We can say that 90 percent of black holes have ceased to be hypothetical objects. Some doubt remains, but still the signal that was caught fits very well with what is predicted by countless simulations of the merger of two black holes in accordance with the general theory of relativity.
This is a strong argument that black holes exist. There is no other explanation for this signal yet. Therefore, it is accepted that black holes exist.”
"Einstein would be very happy"
Gravitational waves were predicted by Albert Einstein (who, by the way, was skeptical about the existence of black holes) as part of his general theory of relativity. In GTO by three spatial dimensions time is added, and the world becomes four-dimensional. According to the theory that turned all physics on its head, gravity is a consequence of the curvature of space-time under the influence of mass.
Einstein proved that any matter moving with acceleration creates a disturbance in space-time - a gravitational wave. This disturbance is greater, the higher the acceleration and mass of the object.
Due to weakness gravitational forces Compared to other fundamental interactions, these waves should have a very small magnitude, difficult to register.
When explaining general relativity to humanities scholars, physicists often ask them to imagine a stretched sheet of rubber onto which massive balls are lowered. The balls press through the rubber, and the stretched sheet (which represents space-time) is deformed. According to general relativity, the entire Universe is rubber, on which every planet, every star and every galaxy leaves dents. Our Earth rotates around the Sun like a small ball, launched to roll around the cone of a funnel formed as a result of “pushing” space-time by a heavy ball.
HANDOUT/Reuters
The heavy ball is the Sun
It is likely that the discovery of gravitational waves, which is the main confirmation of Einstein's theory, is eligible for the Nobel Prize in Physics. “Einstein would be very happy,” said Gabriella Gonzalez, a spokeswoman for the LIGO collaboration.
According to scientists, it is too early to talk about the practical applicability of the discovery. “Although is Heinrich Hertz ( German physicist, who proved the existence electromagnetic waves. - "Gazeta.Ru") could you have thought that there would be a mobile phone? No! “We can’t imagine anything now,” said Valery Mitrofanov, professor at the Faculty of Physics at Moscow State University. M.V. Lomonosov. — I focus on the film “Interstellar”. He is criticized, yes, but even a magic carpet could be imagined wild man. And the magic carpet turned into an airplane, and that’s it. And here we need to imagine something very complex. In Interstellar, one of the points is related to the fact that a person can travel from one world to another. If you imagine this way, do you believe that a person can travel from one world to another, that there can be many universes - anything? I can't answer no. Because a physicist cannot answer such a question “no”! Only if it contradicts some conservation laws! There are options that do not contradict the known ones physical laws. So, there can be travel across worlds!”
, USA
© REUTERS, Handout Gravitational waves are finally discovered
Popular ScienceOscillations in space-time are discovered a century after Einstein predicted them. A new era in astronomy begins.
Scientists have discovered fluctuations in space-time caused by the merger of black holes. This happened a hundred years after Albert Einstein predicted these “gravitational waves” in his general theory of relativity, and a hundred years after physicists began searching for them.
This landmark discovery was announced today by researchers from the Laser Interferometer Gravitational-Wave Observatory (LIGO). They confirmed rumors that had surrounded the analysis of the first set of data they collected for months. Astrophysicists say the discovery of gravitational waves provides new insights into the universe and the ability to recognize distant events that cannot be seen with optical telescopes, but can be felt and even heard as their faint vibrations reach us through space.
“We have detected gravitational waves. We did it!" - announced the executive director scientific team of one thousand people David Reitze, speaking today at a press conference in Washington at the National Science Foundation.
Gravitational waves are perhaps the most elusive phenomenon of Einstein's predictions, and the scientist debated this topic with his contemporaries for decades. According to his theory, space and time form stretchable matter, which bends under the influence of heavy objects. To feel gravity means to fall into the bends of this matter. But can this space-time tremble like the skin of a drum? Einstein was confused; he didn't know what his equations meant. And he changed his point of view several times. But even the most staunch supporters of his theory believed that gravitational waves were in any case too weak to be observed. They cascade outward after certain cataclysms, and as they move, they alternately stretch and compress space-time. But by the time these waves reach the Earth, they stretch and compress every kilometer of space by an insignificant share diameter of the atomic nucleus.
© REUTERS, Hangout LIGO Observatory detector in Hanford, Washington
Detecting these waves required patience and caution. The LIGO observatory fired laser beams back and forth along the four-kilometer (4-kilometer) angled arms of two detectors, one in Hanford, Washington, and the other in Livingston, Louisiana. This was done in search of coincident expansions and contractions of these systems during the passage of gravitational waves. Using state-of-the-art stabilizers, vacuum instruments and thousands of sensors, scientists measured changes in the length of these systems that were as small as one thousandth the size of a proton. Such sensitivity of instruments was unthinkable a hundred years ago. It also seemed incredible in 1968, when Rainer Weiss of the Massachusetts Institute of Technology conceived an experiment called LIGO.
“It is a great miracle that in the end they succeeded. They were able to detect these tiny vibrations!” said University of Arkansas theoretical physicist Daniel Kennefick, who wrote the 2007 book Traveling at the Speed of Thought: Einstein and the Quest for Gravitational Waves (Traveling at the speed of thought. Einstein and the search for gravitational waves).
This discovery marked the beginning new era gravitational wave astronomy. The hope is that we will have better understanding of the formation, composition and galactic role of black holes—those super-dense balls of mass that bend space-time so dramatically that not even light can escape. When black holes come close to each other and merge, they produce a pulse signal—space-time oscillations that increase in amplitude and tone before ending abruptly. Those signals that the observatory can record are in the audio range - however, they are too weak to be heard by the naked ear. You can recreate this sound by running your fingers over the piano keys. “Start with the lowest note and work your way up to the third octave,” Weiss said. "That's what we hear."
Physicists are already surprised by the number and strength of signals recorded on this moment. This means there are more black holes in the world than previously thought. “We were lucky, but I always counted on that kind of luck,” said astrophysicist Kip Thorne, who works at the California Institute of Technology and created LIGO with Weiss and Ronald Drever, also at Caltech. “This usually happens when a completely new window opens in the universe.”
By listening to gravitational waves, we can form completely different ideas about space, and perhaps discover unimaginable cosmic phenomena.
“I can compare this to the first time we pointed a telescope into the sky,” said theoretical astrophysicist Janna Levin of Barnard College, Columbia University. “People realized that there was something there and that it could be seen, but they could not predict the incredible range of possibilities that exist in the universe.” Likewise, Levine noted, the discovery of gravitational waves could show that the universe is “full dark matter, which we cannot easily determine with a telescope.”
The story of the discovery of the first gravitational wave began on a Monday morning in September, and it began with a bang. The signal was so clear and loud that Weiss thought: “No, this is nonsense, nothing will come of it.”
Intensity of emotions
That first gravitational wave swept through the upgraded LIGO's detectors—first at Livingston and seven milliseconds later at Hanford—during a simulation run early on September 14, two days before official start data collection.
The detectors were being tested after an upgrade that lasted five years and cost $200 million. They were equipped with new mirror suspensions for noise reduction and an active feedback to suppress extraneous vibrations in real time. The modernization gave the improved observatory more high level sensitivity compared to the old LIGO, which between 2002 and 2010 found “absolute and pure zero,” as Weiss put it.
When the powerful signal arrived in September, scientists in Europe, where it was morning at that moment, began hastily bombarding their American colleagues with messages over e-mail. When the rest of the group woke up, the news spread very quickly. According to Weiss, almost everyone was skeptical, especially when they saw the signal. It was a true textbook classic, which is why some people thought it was a fake.
The search for gravitational waves has been flawed many times since the late 1960s, when Joseph Weber of the University of Maryland thought he had discovered resonant vibrations in an aluminum cylinder with sensors in response to waves. In 2014, an experiment called BICEP2 announced the discovery of primordial gravitational waves—spacetime ripples from the Big Bang that have now stretched out and become permanently frozen in the geometry of the universe. Scientists from the BICEP2 team announced their discovery with great fanfare, but then their results were subjected to independent verification, during which it turned out that they were wrong and that the signal came from cosmic dust.
When Arizona State University cosmologist Lawrence Krauss heard about the LIGO team's discovery, he initially thought it was a "blind hoax." During the old observatory's operation, simulated signals were surreptitiously inserted into data streams to test the response, without most of the team knowing about it. When Krauss learned from a knowledgeable source that this time it was not a “blind throw in,” he could hardly contain his joyful excitement.
On September 25, he told his 200,000 Twitter followers: “Rumors of a gravitational wave being detected by the LIGO detector. Amazing if true. I’ll give you the details if it’s not a fake.” This is followed by an entry from January 11: “Previous rumors about LIGO have been confirmed by independent sources. Follow the news. Perhaps gravitational waves have been discovered!”
The official position of scientists was this: do not talk about the received signal until there is one hundred percent certainty. Thorne, bound hand and foot by this obligation to secrecy, did not even say anything to his wife. “I celebrated alone,” he said. To begin with, the scientists decided to go back to the very beginning and analyze everything down to the smallest detail in order to find out how the signal propagated through thousands of measurement channels of various detectors, and to understand whether there was anything strange at the moment the signal was detected. They didn't find anything unusual. They also excluded hackers, who would have had the best knowledge of the thousands of data streams in the experiment. “Even when a team does blind throw-ins, they are not perfect enough and leave a lot of marks,” Thorne said. “But there were no traces here.”
In the following weeks, they heard another, weaker signal.
Scientists analyzed the first two signals, and more and more new ones arrived. They presented their research in the journal Physical Review Letters in January. This issue is published online today. According to their estimates, statistical significance The first, most powerful signal exceeds “5-sigma”, which means that researchers are 99.9999% confident in its authenticity.
Listening to gravity
Equations general relativity Einstein's theories are so complex that it took most physicists 40 years to agree: yes, gravitational waves exist, and they can be detected - even theoretically.
At first Einstein thought that objects could not release energy in the form gravitational radiation, but then changed his point of view. In his landmark paper written in 1918, he showed what objects could do this: dumbbell-shaped systems that rotate on two axes simultaneously, such as binaries and supernovae that explode like firecrackers. They can generate waves in space-time.
© REUTERS, Handout Computer model, illustrating the nature of gravitational waves in the Solar System
But Einstein and his colleagues continued to hesitate. Some physicists argued that even if waves existed, the world would vibrate along with them, and it would be impossible to sense them. It wasn't until 1957 that Richard Feynman put the matter to rest by demonstrating in a thought experiment that if gravitational waves existed, they could theoretically be detected. But no one knew how common these dumbbell systems were in outer space, and how strong or weak the resulting waves are. “Ultimately the question was: Will we ever be able to detect them?” said Kennefick.
In 1968, Rainer Weiss was a young professor at MIT and was assigned to teach a course on general relativity. Being an experimentalist, he knew little about it, but suddenly news appeared about Weber's discovery of gravitational waves. Weber built three resonant detectors from aluminum, the size of desk and placed them in different American states. Now he reported that all three detectors detected “the sound of gravitational waves.”
Weiss's students were asked to explain the nature of gravitational waves and express their opinion on the message. Studying the details, he was amazed at the complexity of the mathematical calculations. “I couldn’t figure out what the hell Weber was doing, how the sensors interacted with the gravitational wave. I sat for a long time and asked myself: “What is the most primitive thing I can come up with that would detect gravitational waves?” And then an idea came into my head, which I call conceptual basis LIGO."
Imagine three objects in spacetime, say mirrors at the corners of a triangle. “Send a light signal from one to the other,” Weber said. “See how long it takes to move from one mass to another, and check if the time has changed.” It turns out, the scientist noted, this can be done quickly. “I assigned this to my students as a research assignment. Literally the entire group was able to make these calculations.”
In subsequent years, as other researchers tried to replicate the results of Weber's resonance detector experiment but continually failed (it is unclear what he observed, but it was not gravitational waves), Weiss began preparing a much more precise and ambitious experiment: a gravitational-wave interferometer. The laser beam is reflected from three mirrors installed in the shape of the letter “L” and forms two beams. The interval between the peaks and troughs of light waves precisely indicates the length of the legs of the letter "L", which create the X and Y axes of spacetime. When the scale is stationary, the two light waves are reflected from the corners and cancel each other out. The signal in the detector is zero. But if a gravitational wave passes through the Earth, it stretches the length of one arm of the letter “L” and compresses the length of the other (and vice versa in turn). The mismatch of the two light beams creates a signal in the detector, indicating slight fluctuations in space-time.
At first, fellow physicists expressed skepticism, but the experiment soon gained support from Thorne, whose team of theorists at Caltech was studying black holes and other potential sources of gravitational waves, as well as the signals they generate. Thorne was inspired by Weber's experiment and similar efforts by Russian scientists. After speaking with Weiss at a conference in 1975, “I began to believe that detection of gravitational waves would be successful,” Thorne said. “And I wanted Caltech to be a part of it, too.” He arranged for the institute to hire Scottish experimentalist Ronald Dreaver, who also said he would build a gravitational-wave interferometer. Over time, Thorne, Driver, and Weiss began to work as a team, each solving their share of the countless problems in preparation for the practical experiment. The trio created LIGO in 1984, and when prototypes were built and collaboration began within an ever-expanding team, they received from the National scientific foundation$100 million in funding. Blueprints were drawn up for the construction of a pair of giant L-shaped detectors. A decade later, the detectors started working.
At Hanford and Livingston, at the center of each of the four-kilometer detector arms there is a vacuum, thanks to which the laser, its beam and mirrors are maximally isolated from the constant vibrations of the planet. To be even more on the safe side, LIGO scientists monitor their detectors as they operate with thousands of instruments, measuring everything they can: seismic activity, Atmosphere pressure, lightning, appearance cosmic rays, vibration of equipment, sounds in the area of the laser beam, and so on. They then filter their data from this extraneous background noise. Perhaps the main thing is that they have two detectors, and this allows them to compare the received data, checking them for the presence of matching signals.
Context
Gravitational waves: completed what Einstein started in Bern
SwissInfo 02/13/2016How black holes die
Medium 10/19/2014Inside the vacuum created, even with the lasers and mirrors completely isolated and stabilized, “strange things happen all the time,” says Marco Cavaglià, LIGO deputy spokesman. Scientists must track these “goldfish”, “ghosts”, “obscure sea monsters"and other extraneous vibration phenomena, finding out their source in order to eliminate it. One difficult incident occurred at the testing stage, she said scientific researcher LIGO team member Jessica McIver, who studies such extraneous signals and interference. A series of periodic single-frequency noises often appeared among the data. When she and her colleagues converted the vibrations from the mirrors into audio files, “the phone could be clearly heard ringing,” McIver said. “It turned out that it was the communications advertisers making phone calls inside the laser room.”
Over the next two years, scientists will continue to improve the sensitivity of LIGO's upgraded Laser Interferometer Gravitational-Wave Observatory detectors. And in Italy, a third interferometer called Advanced Virgo will begin operating. One of the answers that the data will help provide is how black holes form. Are they a product of the collapse of the earliest massive stars, or do they appear as a result of collisions within dense star clusters? “These are just two guesses, I believe there will be more when everyone calms down,” Weiss says. When during upcoming work LIGO will begin to accumulate new statistical data, scientists will begin to listen to stories about the origin of black holes that the cosmos will whisper to them.
Judging by its shape and size, the first, loudest pulse originated 1.3 billion light-years from where, after an eternity of slow dance, two black holes, each about 30 times the mass of the sun, finally merged under the influence of mutual gravitational attraction. The black holes were circling faster and faster, like a whirlpool, gradually getting closer. Then the merger occurred, and in the blink of an eye they released gravitational waves with an energy comparable to that of three Suns. This merger was the most powerful energetic phenomenon ever recorded.
“It’s like we’ve never seen the ocean during a storm,” Thorne said. He had been waiting for this storm in spacetime since the 1960s. The feeling Thorne felt as those waves rolled in wasn't exactly excitement, he says. It was something else: a feeling of deep satisfaction.
InoSMI materials contain assessments exclusively of foreign media and do not reflect the position of the InoSMI editorial staff.
A hundred years after the theoretical prediction made by Albert Einstein within the framework of the general theory of relativity, scientists were able to confirm the existence of gravitational waves. The era of a fundamentally new method for studying deep space—gravitational wave astronomy—begins.
There are different discoveries. There are random ones, they are common in astronomy. There are not entirely accidental ones, made as a result of a thorough “combing of the area,” such as the discovery of Uranus by William Herschel. There are serendipal ones - when they were looking for one thing and found another: for example, they discovered America. But special place In science, planned discoveries occupy the forefront. They are based on a clear theoretical prediction. What is predicted is sought primarily in order to confirm the theory. Such discoveries include the discovery of the Higgs boson at the Large Hadron Collider and the detection of gravitational waves using the laser interferometer gravitational-wave observatory LIGO. But in order to register some phenomenon predicted by the theory, you need to have a pretty good understanding of what exactly and where to look, as well as what tools are needed for this.
Gravitational waves are traditionally called a prediction of the general theory of relativity (GTR), and this is indeed so (although now such waves exist in all models that are alternative to or complementary to GTR). The appearance of waves is caused by the finite speed of propagation gravitational interaction(in general relativity this speed is exactly equal to the speed of light). Such waves are disturbances in space-time propagating from a source. For gravitational waves to occur, the source must pulsate or move at an accelerated rate, but in a certain way. Let's say movements with perfect spherical or cylindrical symmetry are not suitable. There are quite a lot of such sources, but often they have a small mass, insufficient to generate a powerful signal. After all, gravity is the weakest of the four fundamental interactions, so it is very difficult to register a gravitational signal. In addition, for registration it is necessary that the signal changes quickly over time, that is, it has a sufficiently high frequency. Otherwise, we will not be able to register it, since the changes will be too slow. This means that the objects must also be compact.
Initially, great enthusiasm was generated by supernova explosions that occur in galaxies like ours every few decades. This means that if we can achieve a sensitivity that allows us to see a signal from a distance of several million light years, we can count on several signals per year. But later it turned out that initial estimates of the power of energy release in the form of gravitational waves during a supernova explosion were too optimistic, and such a weak signal could only be detected if a supernova had broken out in our Galaxy.
Another massive option compact objects moving rapidly are neutron stars or black holes. We can see either the process of their formation, or the process of interaction with each other. The last stages of the collapse of stellar cores, leading to the formation of compact objects, as well as the last stages of the merger of neutron stars and black holes, have a duration of the order of several milliseconds (which corresponds to a frequency of hundreds of hertz) - just what is needed. In this case, a lot of energy is released, including (and sometimes mainly) in the form of gravitational waves, since massive compact bodies make certain rapid movements. These are our ideal sources.
True, supernovae erupt in the Galaxy once every few decades, mergers of neutron stars occur once every couple of tens of thousands of years, and black holes merge with each other even less often. But the signal is much more powerful, and its characteristics can be calculated quite accurately. But now we need to be able to see the signal from a distance of several hundred million light years in order to cover several tens of thousands of galaxies and detect several signals in a year.
Having decided on the sources, we will begin to design the detector. To do this, you need to understand what a gravitational wave does. Without going into detail, we can say that the passage of a gravitational wave causes a tidal force (ordinary lunar or solar tides are a separate phenomenon, and gravitational waves have nothing to do with it). So you can take, for example, a metal cylinder, equip it with sensors and study its vibrations. This is not difficult, which is why such installations began to be made half a century ago (they are also available in Russia; now an improved detector developed by Valentin Rudenko’s team from the SAI MSU is being installed in the Baksan underground laboratory). The problem is that such a device will see the signal without any gravitational waves. There are a lot of noises that are difficult to deal with. It is possible (and has been done!) to install the detector underground, try to isolate it, cool it to low temperatures, but still, in order to exceed the noise level, a very powerful gravitational wave signal would be needed. But powerful signals come rarely.
Therefore, the choice was made in favor of another scheme, which was put forward in 1962 by Vladislav Pustovoit and Mikhail Herzenstein. In an article published in JETP (Journal of Experimental and Theoretical Physics), they proposed using a Michelson interferometer to detect gravitational waves. The laser beam runs between the mirrors in the two arms of the interferometer, and then the beams from different arms are added. By analyzing the result of beam interference, the relative change in arm lengths can be measured. These are very precise measurements, so if you beat the noise, you can achieve fantastic sensitivity.
In the early 1990s, it was decided to build several detectors using this design. The first to go into operation were relatively small installations, GEO600 in Europe and TAMA300 in Japan (the numbers correspond to the length of the arms in meters) to test the technology. But the main players were to be the LIGO installations in the USA and VIRGO in Europe. The size of these instruments is already measured in kilometers, and the final planned sensitivity should allow seeing dozens, if not hundreds of events per year.
Why are multiple devices needed? Primarily for cross-validation, since there are local noises (e.g. seismic). Simultaneous recording of the signal in the northwestern United States and Italy would be excellent evidence of its external origin. But there is a second reason: gravitational wave detectors are very poor at determining the direction to the source. But if there are several detectors spaced apart, it will be possible to indicate the direction quite accurately.
Laser giants
In their original form, the LIGO detectors were built in 2002, and the VIRGO detectors in 2003. According to the plan, this was only the first stage. All installations operated for several years, and in 2010-2011 they were stopped for modifications, in order to then reach the planned high sensitivity. The LIGO detectors were the first to operate in September 2015, VIRGO should join in the second half of 2016, and from this stage the sensitivity allows us to hope for recording at least several events per year.
After LIGO began operating, the expected burst rate was approximately one event per month. Astrophysicists estimated in advance that the first expected events would be black hole mergers. This is due to the fact that black holes are usually ten times heavier than neutron stars, the signal is more powerful, and it is “visible” from great distances, which more than compensates for the lower rate of events per galaxy. Fortunately, we didn't have to wait long. On September 14, 2015, both installations registered an almost identical signal, named GW150914.
With pretty help simple analysis data such as black hole masses, signal strength, and distance to the source can be obtained. The mass and size of black holes are related very simply and well in a known manner, and from the signal frequency one can immediately estimate the size of the energy release region. IN in this case the size indicated that a black hole with a mass of more than 60 solar masses was formed from two holes with a mass of 25-30 and 35-40 solar masses. Knowing this data, you can get full energy splash. Almost three solar masses were converted into gravitational radiation. This corresponds to the luminosity of 1023 solar luminosities - approximately the same amount as all the stars in the visible part of the Universe emit during this time (hundredths of a second). And from the known energy and magnitude of the measured signal, the distance is obtained. The large mass of the merged bodies made it possible to register an event that occurred in a distant galaxy: the signal took approximately 1.3 billion years to reach us.
More detailed analysis allows us to clarify the mass ratio of black holes and understand how they rotated around their axis, as well as determine some other parameters. In addition, the signal from two installations makes it possible to approximately determine the direction of the burst. Unfortunately, the accuracy here is not very high yet, but with the commissioning of the updated VIRGO it will increase. And in a few years, the Japanese KAGRA detector will begin to receive signals. Then one of the LIGO detectors (there were originally three, one of the installations was dual) will be assembled in India, and it is expected that many dozens of events will be recorded per year.
The era of new astronomy
At the moment the most important result LIGO's work is confirmation of the existence of gravitational waves. In addition, the very first burst made it possible to improve the restrictions on the mass of the graviton (in general relativity it has zero mass), as well as to more strongly limit the difference between the speed of propagation of gravity and the speed of light. But scientists hope that already in 2016 they will be able to obtain a lot of new astrophysical data using LIGO and VIRGO.
First, data from gravitational wave observatories provide a new avenue for studying black holes. If previously it was only possible to observe the flows of matter in the vicinity of these objects, now you can directly “see” the process of merging and “calming” the resulting black hole, how its horizon fluctuates, taking on its final shape (determined by rotation). Probably, until the discovery of Hawking evaporation of black holes (for now this process remains a hypothesis), the study of mergers will provide better direct information about them.
Secondly, observations of neutron star mergers will yield a lot of new, extremely necessary information about these objects. For the first time, we will be able to study neutron stars the way physicists study particles: watching them collide to understand how they work inside. The mystery of the structure of the interiors of neutron stars worries both astrophysicists and physicists. Our understanding nuclear physics and the behavior of matter at ultra-high density is incomplete without resolving this issue. It is likely that gravitational wave observations will play a key role here.
It is believed that neutron star mergers are responsible for short cosmological gamma-ray bursts. In rare cases, it will be possible to simultaneously observe an event both in the gamma range and on gravitational wave detectors (the rarity is due to the fact that, firstly, the gamma signal is concentrated into a very narrow beam, and it is not always directed at us, but secondly, we will not register gravitational waves from very distant events). Apparently, it will take several years of observation to be able to see this (although, as usual, you may be lucky and it will happen today). Then, among other things, we will be able to very accurately compare the speed of gravity with the speed of light.
Thus, laser interferometers together will work as a single gravitational-wave telescope, bringing new knowledge to both astrophysicists and physicists. Well, for the discovery of the first bursts and their analysis, sooner or later a well-deserved award will be awarded Nobel Prize.
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The official day of discovery (detection) of gravitational waves is February 11, 2016. It was then, at a press conference held in Washington, that the leaders of the LIGO collaboration announced that a team of researchers had managed to record this phenomenon for the first time in human history.
Prophecies of the great Einstein
The fact that gravitational waves exist was suggested by Albert Einstein at the beginning of the last century (1916) within the framework of his General Theory of Relativity (GTR). One can only marvel at the brilliant abilities of the famous physicist, who, with a minimum of real data, was able to draw such far-reaching conclusions. Among many other predicted physical phenomena that were confirmed in the next century (slowing down the flow of time, changing the direction of electromagnetic radiation in gravitational fields etc.) until recently it was not possible to practically detect the presence of this type of wave interaction between bodies.
Is gravity an illusion?
In general, in the light of the Theory of Relativity, gravity can hardly be called a force. disturbances or curvatures of the space-time continuum. A good example A stretched piece of fabric can serve as an illustration of this postulate. Under the weight of a massive object placed on such a surface, a depression is formed. Other objects, when moving near this anomaly, will change the trajectory of their movement, as if being “attracted”. And the greater the weight of the object (the greater the diameter and depth of the curvature), the higher the “force of attraction”. As it moves across the fabric, one can observe the appearance of diverging “ripples”.
Something similar happens in outer space. Any rapidly moving massive matter is a source of fluctuations in the density of space and time. A gravitational wave with a significant amplitude is formed by bodies with extremely large masses or when moving with enormous accelerations.
physical characteristics
Fluctuations in the space-time metric manifest themselves as changes in the gravitational field. This phenomenon is otherwise called space-time ripples. The gravitational wave affects the encountered bodies and objects, compressing and stretching them. The magnitude of the deformation is very insignificant - about 10 -21 from the original size. The whole difficulty of detecting this phenomenon was that researchers needed to learn how to measure and record such changes using appropriate equipment. The power of gravitational radiation is also extremely small - for the entire solar system it is several kilowatts.
The speed of propagation of gravitational waves depends slightly on the properties of the conducting medium. The amplitude of oscillations gradually decreases with distance from the source, but never reaches zero. The frequency ranges from several tens to hundreds of hertz. The speed of gravitational waves in the interstellar medium approaches the speed of light.
Circumstantial evidence
The first theoretical confirmation of the existence of gravitational waves was obtained by the American astronomer Joseph Taylor and his assistant Russell Hulse in 1974. Studying the vastness of the Universe using the Arecibo Observatory radio telescope (Puerto Rico), researchers discovered the pulsar PSR B1913+16, which is dual system neutron stars orbiting general center mass with constant angular velocity(enough rare case). Every year the circulation period, originally 3.75 hours, is reduced by 70 ms. This value is fully consistent with the conclusions from the general relativity equations, which predict an increase in the rotation speed of such systems due to the expenditure of energy on the generation of gravitational waves. Subsequently, several double pulsars and white dwarfs with similar behavior were discovered. Radio astronomers D. Taylor and R. Hulse were awarded the Nobel Prize in Physics in 1993 for discovering new possibilities for studying gravitational fields.
Escaping gravitational wave
The first announcement about the detection of gravitational waves came from University of Maryland scientist Joseph Weber (USA) in 1969. For these purposes, he used two gravitational antennas of his own design, separated by a distance of two kilometers. The resonant detector was a well-vibration-insulated solid two-meter aluminum cylinder equipped with sensitive piezoelectric sensors. The amplitude of the oscillations allegedly recorded by Weber turned out to be more than a million times higher than the expected value. Attempts by other scientists to repeat the “success” using similar equipment American physicist positive results didn't bring it. A few years later, Weber’s work in this area was recognized as untenable, but gave impetus to the development of the “gravitational boom”, which attracted many specialists to this area of research. By the way, Joseph Weber himself was sure until the end of his days that he received gravitational waves.
Improving receiving equipment
In the 70s, scientist Bill Fairbank (USA) developed the design of a gravitational wave antenna, cooled using SQUIDS - ultra-sensitive magnetometers. The technologies existing at that time did not allow the inventor to see his product realized in “metal”.
Made according to this principle gravity detector Auriga at the National Legnara Laboratory (Padua, Italy). The design is based on an aluminum-magnesium cylinder, 3 meters long and 0.6 m in diameter. The receiving device weighing 2.3 tons is suspended in an insulated vacuum chamber cooled almost to absolute zero. To record and detect shocks, an auxiliary kilogram resonator and a computer-based measuring complex are used. The stated sensitivity of the equipment is 10 -20.
Interferometers
The operation of interference detectors of gravitational waves is based on the same principles on which the Michelson interferometer operates. The laser beam emitted by the source is divided into two streams. After multiple reflections and travels along the arms of the device, the flows are again brought together, and based on the final one it is judged whether any disturbances (for example, a gravitational wave) affected the course of the rays. Similar equipment has been created in many countries:
- GEO 600 (Hannover, Germany). The length of the vacuum tunnels is 600 meters.
- TAMA (Japan) with shoulders of 300 m.
- VIRGO (Pisa, Italy) is a joint French-Italian project launched in 2007 with three kilometers of tunnels.
- LIGO (USA, Pacific Coast), which has been hunting for gravitational waves since 2002.
The latter is worth considering in more detail.
LIGO Advanced
The project was created on the initiative of scientists from the Massachusetts and Californian technological institutes. It includes two observatories, separated by 3 thousand km, in and Washington (the cities of Livingston and Hanford) with three identical interferometers. The length of perpendicular vacuum tunnels is 4 thousand meters. These are the largest such structures currently in operation. Until 2011, numerous attempts to detect gravitational waves did not bring any results. The significant modernization carried out (Advanced LIGO) increased the sensitivity of the equipment in the range of 300-500 Hz by more than five times, and in the low-frequency region (up to 60 Hz) by almost an order of magnitude, reaching the coveted value of 10 -21. The updated project started in September 2015, and the efforts of more than a thousand collaboration employees were rewarded with the results obtained.
Gravitational waves detected
On September 14, 2015, advanced LIGO detectors, with an interval of 7 ms, recorded gravitational waves reaching our planet from the largest event that occurred on the outskirts of the observable Universe - the merger of two large black holes with masses 29 and 36 times greater than the mass of the Sun. During the process, which took place more than 1.3 billion years ago, about three solar masses of matter were consumed in a matter of fractions of a second by emitting gravitational waves. The recorded initial frequency of gravitational waves was 35 Hz, and the maximum peak value reached 250 Hz.
The results obtained were repeatedly subjected to comprehensive verification and processing, and alternative interpretations of the data obtained were carefully eliminated. Finally, last year the direct registration of the phenomenon predicted by Einstein was announced to the world community.
A fact illustrating the titanic work of researchers: the amplitude of fluctuations in the size of the interferometer arms was 10 -19 m - this value is the same number of times smaller than the diameter of an atom, as the atom itself is smaller than an orange.
Future prospects
This discovery once again confirms that General theory relativity is not just a set of abstract formulas, but fundamentally A New Look on the essence of gravitational waves and gravity in general.
IN further research Scientists have high hopes for the ELSA project: the creation of a giant orbital interferometer with arms of about 5 million km, capable of detecting even minor disturbances in gravitational fields. Activation of work in this direction can tell a lot of new things about the main stages of the development of the Universe, about processes that are difficult or impossible to observe in traditional ranges. There is no doubt that black holes, whose gravitational waves will be detected in the future, will tell a lot about their nature.
To study relict gravitational radiation, which can tell about the first moments of our world after Big Bang, more sensitive space instruments will be required. Such a project exists ( Big Bang Observer), but its implementation, according to experts, is possible no earlier than in 30-40 years.