Gravitational waves - discovered! Gravitational waves: the most important thing about a colossal discovery.

One hundred years after the theoretical prediction, which, within general theory relativity was made by Albert Einstein, 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 planned discoveries occupy a special place in science. 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 finiteness of the speed of propagation of 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 option for massive compact objects that move quickly 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 detection 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 fairly 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 in a very simple and well-known way, and from the signal frequency one can immediately estimate the size of the energy release region. In this case, the size indicated that from two holes with a mass of 25-30 and 35-40 solar masses, a black hole with a mass of more than 60 solar masses was formed. Knowing these data, one can obtain the total energy of the burst. 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.

A more detailed analysis makes it possible 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 provide a lot of new, urgently needed 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 of nuclear physics and the behavior of matter at ultrahigh densities 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, sooner or later a well-deserved Nobel Prize will be awarded for the discovery of the first bursts and their analysis.

2198

On Thursday, February 11, a group of scientists from the international project LIGO Scientific Collaboration announced that they had succeeded, the existence of which was predicted by Albert Einstein back in 1916. According to the researchers, on September 14, 2015, they recorded a gravitational wave that was caused by the collision of two black holes weighing 29 and 36 times the mass of the Sun, after which they merged into one large black hole. According to them, this supposedly happened 1.3 billion years ago at a distance of 410 Megaparsecs from our galaxy.

LIGA.net spoke in detail about gravitational waves and the large-scale discovery Bogdan Hnatyk, Ukrainian scientist, astrophysicist, Doctor of Physical and Mathematical Sciences, leading researcher at the Kyiv Astronomical Observatory national university named after Taras Shevchenko, who headed the observatory from 2001 to 2004.

Theory in simple language

Physics studies the interaction between bodies. It has been established that there are four types of interaction between bodies: electromagnetic, strong and weak nuclear interaction and gravitational interaction, which we all feel. Due to gravitational interaction, the planets revolve around the Sun, the bodies have weight and fall to the ground. Humans are constantly faced with gravitational interaction.

In 1916, 100 years ago, Albert Einstein built a theory of gravity that improved Newton's theory of gravity, made it mathematically correct: it began to meet all the requirements of physics, and began to take into account the fact that gravity propagates at a very high, but finite speed. This is rightfully one of Einstein's greatest achievements, since he built a theory of gravity that corresponds to all the phenomena of physics that we observe today.

This theory also suggested the existence gravitational waves. The basis of this prediction was that gravitational waves exist as a result of the gravitational interaction that occurs due to the merger of two massive bodies.

What is a gravitational wave

In complex language this is the excitation of the space-time metric. “Say, space has a certain elasticity and waves can run through it. It’s similar to when we throw a pebble into water and waves scatter from it,” the doctor of physical and mathematical sciences told LIGA.net.

Scientists were able to experimentally prove that a similar oscillation took place in the Universe and a gravitational wave ran in all directions. “Astrophysically, for the first time, the phenomenon of such a catastrophic evolution of a binary system was recorded, when two objects merge into one, and this merger leads to a very intense release of gravitational energy, which then spreads in space in the form of gravitational waves,” the scientist explained.

What it looks like (photo - EPA)

These gravitational waves are very weak and in order for them to shake space-time, the interaction of very large and massive bodies is necessary so that the intensity of the gravitational field is high at the point of generation. But, despite their weakness, the observer after a certain time (equal to the distance to the interaction divided by the speed of the signal) will register this gravitational wave.

Let's give an example: if the Earth fell on the Sun, then gravitational interaction would occur: gravitational energy would be released, a gravitational spherically symmetrical wave would form, and the observer would be able to register it. “A similar, but unique, from the point of view of astrophysics, phenomenon occurred here: two massive bodies collided - two black holes,” Gnatyk noted.

Let's get back to theory

A black hole is another prediction of Einstein's general theory of relativity, which provides that a body that has enormous mass, but this mass is concentrated in a small volume, is capable of significantly distorting the space around it, up to its closure. That is, it was assumed that when a critical concentration of the mass of this body is reached - such that the size of the body will be less than the so-called gravitational radius, then the space around this body will be closed and its topology will be such that no signal from it will spread beyond the closed space can not.

"That is, a black hole, in simple words, is a massive object that is so heavy that it closes space-time around itself,” the scientist says.

And we, according to him, can send any signals to this object, but he cannot send them to us. That is, no signals can go beyond the black hole.

A black hole lives according to ordinary physical laws, but as a result of strong gravity, not a single material body, not even a photon, is able to go beyond this critical surface. Black holes are formed during the evolution of ordinary stars, when the central core collapses and part of the star's matter, collapsing, turns into a black hole, and the other part of the star is ejected in the form of a supernova shell, turning into the so-called “outburst” of a supernova.

How we saw the gravitational wave

Let's give an example. When we have two floats on the surface of the water and the water is calm, the distance between them is constant. When a wave arrives, it displaces these floats and the distance between the floats will change. The wave has passed - and the floats return to their previous positions, and the distance between them is restored.

A gravitational wave propagates in space-time in a similar way: it compresses and stretches bodies and objects that meet on its path. “When a certain object is encountered along the path of a wave, it is deformed along its axes, and after its passage it returns to its previous shape. Under the influence of a gravitational wave, all bodies are deformed, but these deformations are very insignificant,” says Gnatyk.

When the wave that scientists recorded passed, then relative size bodies in space changed by an amount of the order of 1 times 10 to the minus 21st power. For example, if you take a meter ruler, then it has shrunk by an amount that is its size multiplied by 10 to the minus 21st power. This is a very tiny amount. And the problem was that scientists needed to learn how to measure this distance. Conventional methods gave an accuracy of the order of 1 in 10 to the 9th power of millions, but here much higher accuracy is needed. For this purpose, so-called gravitational antennas (gravitational wave detectors) were created.

LIGO Observatory (photo - EPA)

The antenna that recorded gravitational waves is built in this way: there are two pipes, approximately 4 kilometers in length, located in the shape of the letter “L”, but with the same arms and at right angles. When a gravitational wave hits a system, it deforms the wings of the antenna, but depending on its orientation, it deforms one more and the other less. And then a path difference arises, the interference pattern of the signal changes - a total positive or negative amplitude appears.

“That is, the passage of a gravitational wave is similar to a wave on water passing between two floats: if we measured the distance between them during and after the passage of the wave, we would see that the distance would change, and then become the same again,” he said Gnatyk.

Here the relative change in the distance of the two wings of the interferometer, each of which is about 4 kilometers in length, is measured. And only very precise technologies and systems can measure such microscopic displacement of the wings caused by a gravitational wave.

At the edge of the Universe: where did the wave come from?

Scientists recorded the signal using two detectors, which are located in two states in the United States: Louisiana and Washington, at a distance of about 3 thousand kilometers. Scientists were able to estimate where and from what distance this signal came. Estimates show that the signal came from a distance of 410 Megaparsecs. A megaparsec is the distance light travels in three million years.

To make it easier to imagine: the closest active galaxy to us with a supermassive black hole in the center is Centaurus A, which is located at a distance of four Megaparsecs from ours, while the Andromeda Nebula is at a distance of 0.7 Megaparsecs. “That is, the distance from which the gravitational wave signal came is so great that the signal traveled to Earth for approximately 1.3 billion years. These are cosmological distances that reach about 10% of the horizon of our Universe,” the scientist said.

At this distance, in some distant galaxy, two black holes merged. These holes, on the one hand, were relatively small in size, and on the other hand, the large signal amplitude indicates that they were very heavy. It was established that their masses were 36 and 29 solar masses, respectively. The mass of the Sun, as is known, is equal to 2 times 10 to the 30th power of a kilogram. After the merger, these two bodies merged and now in their place a single black hole has formed, which has a mass equal to 62 solar masses. At the same time, approximately three masses of the Sun splashed out in the form of gravitational wave energy.

Who made the discovery and when

Scientists from the international LIGO project managed to detect a gravitational wave on September 14, 2015. LIGO (Laser Interferometry Gravitation Observatory) is an international project in which a number of states take part, making a certain financial and scientific contribution, in particular the USA, Italy, Japan, which are advanced in the field of this research.

Professors Rainer Weiss and Kip Thorne (photo - EPA)

The following picture was recorded: the wings of the gravitational detector shifted as a result of the actual passage of a gravitational wave through our planet and through this installation. This was not reported then, because the signal had to be processed, “cleaned”, its amplitude found and checked. This is a standard procedure: from the actual discovery to the announcement of the discovery, it takes several months to issue a substantiated statement. “No one wants to spoil their reputation. This is all secret data, before the publication of which no one knew about it, there were only rumors,” Hnatyk noted.

Story

Gravitational waves have been studied since the 70s of the last century. During this time, a number of detectors were created and a series of basic research. In the 80s, the American scientist Joseph Weber built the first gravitational antenna in the form of an aluminum cylinder, which was about several meters in size, equipped with piezo sensors that were supposed to record the passage of a gravitational wave.

The sensitivity of this device was a million times worse than current detectors. And, of course, he could not really detect the wave then, although Weber declared that he had done it: the press wrote about it and a “gravitational boom” occurred - the world immediately began to build gravitational antennas. Weber encouraged other scientists to take up gravitational waves and continue experiments on this phenomenon, which made it possible to increase the sensitivity of detectors a million times.

However, the phenomenon of gravitational waves itself was recorded in the last century, when scientists discovered a double pulsar. This was an indirect recording of the fact that gravitational waves exist, proven through astronomical observations. The pulsar was discovered by Russell Hulse and Joseph Taylor in 1974 during observations with the Arecibo Observatory radio telescope. Scientists were awarded Nobel Prize in 1993 "for the discovery of a new type of pulsars, which provided new opportunities in the study of gravity."

Research in the world and Ukraine

In Italy, a similar project called Virgo is nearing completion. Japan also intends to launch a similar detector in a year, and India is also preparing such an experiment. That is, similar detectors exist in many parts of the world, but they have not yet reached the sensitivity mode so that we can talk about detecting gravitational waves.

“Officially, Ukraine is not part of LIGO and also does not participate in the Italian and Japanese projects. Among such fundamental areas, Ukraine is now participating in the LHC (Large Hadron Collider) project and in CERN (we will officially become a participant only after paying the entrance fee) ", Doctor of Physical and Mathematical Sciences Bohdan Gnatyk told LIGA.net.

According to him, since 2015 Ukraine has been a full member of the international collaboration CTA (Cerenkov Telescope Array), which is building a modern multi telescope TeV long gamma range (with photon energies up to 1014 eV). “The main sources of such photons are precisely the vicinity of supermassive black holes, the gravitational radiation of which was first recorded by the LIGO detector. Therefore, the opening of new windows in astronomy - gravitational wave and multi TeV“nogo electromagnetic technology promises us many more discoveries in the future,” the scientist adds.

What's next and how will new knowledge help people? Scientists disagree. Some say that this is just the next step in understanding the mechanisms of the Universe. Others see this as the first steps towards new technologies for moving through time and space. One way or another - this is a discovery in Once again has proven how little we understand and how much remains to be learned.

, USA

Gravitational waves are finally discovered

Popular Science

Oscillations in space-time are discovered a century after Einstein predicted them. Begins new era in astronomy.

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!" “David Reitze, executive director of the 1,000-person research team, announced 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 Earth, they have stretched and compressed every kilometer of space by a tiny fraction of its diameter. atomic nucleus.

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 seemed incredible even 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 theoretical physicist from the University of Arkansas, Daniel Kennefick, who wrote the 2007 book Traveling at the Speed of Thought: Einstein and the Quest for Gravitational Waves.

This discovery marked the beginning of a new era of 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 that have been recorded so far. 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 of dark matter that we can't easily detect 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 data collection officially began.

The detectors were being tested after an upgrade that lasted five years and cost $200 million. They are equipped with new mirror suspensions for noise reduction and an active feedback system 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.

False claims in the search for gravitational waves have been made repeatedly since the late 1960s, when Joseph Weber of the University of Maryland thought he had discovered resonant vibrations in an aluminum cylinder containing sensors in response to the waves. In 2014, an experiment called BICEP2 took place, the results of which announced the discovery of primordial gravitational waves - space-time oscillations from big bang, which have now stretched out and are 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 operation of the old observatory, simulated signals were surreptitiously inserted into data streams to test the response, and most of The team didn't know 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, the statistical significance of the first, most powerful signal exceeds 5-sigma, which means that the researchers are 99.9999% confident in its authenticity.

Listening to gravity

Einstein's equations of general relativity are so complex that it took most physicists 40 years to agree that, yes, gravitational waves exist and can be detected—even theoretically.

At first, Einstein thought that objects could not release energy in the form of gravitational radiation, but then he 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.

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-shaped systems were in outer space, or how strong or weak the resulting waves were. “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 will detect gravitational waves?” And then I came up with an idea that I call the conceptual basis of 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. This trio created LIGO in 1984, and when they were built prototypes and began collaborating within an ever-expanding team, receiving $100 million in funding from the National Science Foundation in the early 1990s. Blueprints have been drawn up to build a pair of giant detectors. L-shaped. 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 further hedge their bets, LIGO scientists monitor their detectors as they operate with thousands of instruments, measuring everything they can: seismic activity, barometric pressure, lightning, cosmic rays, vibration of equipment, sounds in the vicinity 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 02/13/2016

How black holes die

Medium 10/19/2014
Inside 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 vibrational phenomena, finding out their source in order to eliminate it. One hard case occurred during the testing phase, said LIGO researcher 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 are they created by collisions within dense star clusters? “These are just two guesses, I believe there will be more when everyone calms down,” Weiss says. As LIGO's upcoming work begins to accumulate new statistics, scientists will begin to listen to the stories the cosmos whispers to them about the origins of black holes.

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 has 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.

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 gravitation are one and the same thing. 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 in 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. Gravitational field strength - acceleration 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 traveling 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 in amplitude smaller size 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:

Gravitational waves are changes in the gravitational field that propagate like waves. They are emitted by moving masses, but after radiation they are separated from them and exist independently of these masses. Mathematically related to the perturbation of spacetime metrics and can be described as "spacetime ripples".
In general relativity and most others modern theories In gravity, gravitational waves are generated by the motion of massive bodies with variable acceleration. Gravitational waves propagate freely in space at the speed of light. Due to the relative weakness of gravitational forces (compared to others), these waves have a very small magnitude, which is difficult to register.
Gravitational waves are predicted by the general theory of relativity (GR) and many other theories of gravity. They were first directly discovered in September 2015 by LIGO's twin detectors, which detected gravitational waves likely resulting from the merger of two black holes to form one more massive rotating black hole. black hole. Indirect evidence of their existence has been known since the 1970s - General Relativity predicts rates of convergence of close systems of double stars that coincide with observations due to the loss of energy due to the emission of gravitational waves. Direct registration of gravitational waves and their use to determine the parameters of astrophysical processes is an important task of modern physics and astronomy.
Within the framework of general relativity, gravitational waves are described by solutions of wave-type Einstein equations, which represent a perturbation of the space-time metric moving at the speed of light (in the linear approximation). The manifestation of this disturbance should be, in particular, a periodic change in the distance between two freely falling (that is, not influenced by any forces) test masses. The amplitude h of a gravitational wave is a dimensionless quantity - a relative change in distance. The predicted maximum amplitudes of gravitational waves from astrophysical objects (for example, compact binary systems) and phenomena (supernova explosions, neutron star mergers, star captures by black holes, etc.) when measured in the Solar System are very small (h = 10−18-10 −23). A weak (linear) gravitational wave, according to the general theory of relativity, transfers energy and momentum, moves at the speed of light, is transverse, quadrupole and is described by two independent components located at an angle of 45° to each other (has two directions of polarization).
Different theories predict the speed of propagation of gravitational waves differently. In general relativity, it is equal to the speed of light (in the linear approximation). In other theories of gravity, it can take any value, including infinity. According to the first registration of gravitational waves, their dispersion turned out to be compatible with a massless graviton, and the speed was estimated to be equal to the speed of light.