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, which was caused by the collision of two black holes with a mass of 29 and 36 times the mass of the Sun, after which they merged into one large black hole. According to them, this happened supposedly 1.3 billion years ago at a distance of 410 Megaparsecs from our galaxy.
LIGA.net spoke in detail about gravitational waves and a large-scale discovery Bohdan Hnatyk, Ukrainian scientist, astrophysicist, doctor of physical and mathematical sciences, leading researcher at the Astronomical Observatory of Taras Shevchenko National University of Kyiv, who headed the observatory from 2001 to 2004.
Theory in plain 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 the gravitational interaction, the planets revolve around the Sun, the bodies have weight and fall to the ground. Human beings are constantly confronted 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, began to take into account the fact that gravity propagates at a very high, but finite speed. This is rightfully one of Einstein's most ambitious achievements, as 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 a complex language, this is the excitation of the space-time metric. "Let's say space has a certain elasticity and waves can run through it. It's like when we throw a pebble into the water and waves scatter from it," Doctor of Physical and Mathematical Sciences told LIGA.net.
Scientists managed to experimentally prove that such a fluctuation took place in the Universe and a gravitational wave ran in all directions. "The astrophysical method was the first to record the phenomenon of such a catastrophic evolution of a binary system, when two objects merge into one, and this merger leads to a very intense release of gravitational energy, which then propagates 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 oscillate space-time, the interaction of very large and massive bodies is necessary so that the gravitational field strength is large at the place 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 a gravitational interaction would occur: gravitational energy would be released, a gravitational spherically symmetric wave would form, and the observer could register it. "Here, a similar, but unique, from the point of view of astrophysics, phenomenon occurred: two massive bodies - two black holes - collided," Gnatyk noted.
Back to theory
A black hole is another prediction of Einstein's general theory of relativity, which provides that a body that has a huge mass, but this mass is concentrated in a small volume, can significantly distort 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 close and its topology will be such that no signal from it will spread outside the closed space can not.
"That is, a black hole, in simple terms, 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 us. That is, no signals can go beyond the black hole.
A black hole lives according to the usual physical laws, but as a result of strong gravity, not a single material body, 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 "flash" of a supernova.
How we saw the gravitational wave
Let's take 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 comes, it shifts 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 a similar way in space-time: it compresses and stretches the bodies and objects that meet on its way. “When a certain object is encountered on the path of a wave, it deforms along its axes, and after it passes, it returns to its previous shape. Under the influence of a gravitational wave, all bodies are deformed, but these deformations are very insignificant,” says Hnatyk.
When the wave passed, which was recorded by scientists, the relative size of the bodies in space changed by a value of the order of 1 times 10 to the minus 21st power. For example, if you take a meter ruler, then it shrank by such a value that it was its size, multiplied by 10 to the minus 21st degree. This is a very small amount. And the problem was that scientists had to learn how to measure this distance. Conventional methods gave an accuracy of the order of 1 to 10 to the 9th power of a million, but here a much higher accuracy is needed. To do this, created the so-called gravitational antennas (detectors of gravitational waves).
LIGO observatory (photo - EPA)
The antenna that recorded the gravitational waves is constructed in this way: there are two tubes, about 4 kilometers long, arranged in the shape of the letter "L", but with the same arms and at right angles. When a gravitational wave falls on the system, it deforms the wings of the antenna, but depending on its orientation, it deforms one more and the other less. And then there is a path difference, the interference pattern of the signal changes - there is a total positive or negative amplitude.
“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,” said Gnatyk.
It also measures the relative change in the distance of the two wings of the interferometer, each of which is about 4 kilometers long. And only very precise technologies and systems can measure such a 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 in the United States are located in two 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 that is 410 Megaparsecs. A megaparsec is the distance light travels in three million years.
To make it easier to imagine: the nearest active galaxy to us with a supermassive black hole in the center is Centaurus A, which is 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 went to the Earth for about 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 amplitude of the signal indicates that they were very heavy. It was established that their masses were respectively 36 and 29 solar masses. The mass of the Sun, as you know, is a value that 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 that have made a certain financial and scientific contribution take part, in particular the USA, Italy, Japan, which are advanced in the field of these studies.
Professors Rainer Weiss and Kip Thorne (photo - EPA)
The following picture was recorded: there was a displacement of the wings of the gravitational detector, 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 a real discovery to an announcement of a discovery, it takes several months to issue a valid claim. "No one wants to spoil their reputation. These are all secret data, before the publication of which - no one knew about them, there were only rumors," Hnatyk said.
Story
Gravitational waves have been studied since the 70s of the last century. During this time, a number of detectors were created and a number of fundamental studies were carried out. In the 80s, the American scientist Joseph Weber built the first gravitational antenna in the form of an aluminum cylinder, which had a size of the order of several meters, equipped with piezo sensors that were supposed to record the passage of a gravitational wave.
The sensitivity of this instrument was a million times worse than current detectors. And, of course, he could not really fix the wave at that time, although Weber also said that he did it: the press wrote about it and there was a "gravitational boom" - the world immediately began to build gravitational antennas. Weber encouraged other scientists to study gravitational waves and continue their experiments on this phenomenon, which made it possible to increase the sensitivity of detectors a million times.
However, the very phenomenon of gravitational waves was recorded in the last century, when scientists discovered a double pulsar. It was an indirect registration of the fact that gravitational waves exist, proven through astronomical observations. The pulsar was discovered by Russell Hulse and Joseph Taylor in 1974 while observing with the Arecibo Observatory radio telescope. Scientists were awarded the Nobel Prize in 1993 "for the discovery of a new type of pulsar, which gave new possibilities in the study of gravity."
Research in the world and Ukraine
In Italy, a similar project called Virgo is close to completion. Japan also intends to launch a similar detector in a year, India is also preparing such an experiment. That is, in many parts of the world there are similar detectors, but they have not yet reached that sensitivity mode so that we can talk about fixing gravitational waves.
"Officially, Ukraine is not a member of LIGO and also does not participate in the Italian and Japanese projects. Among such fundamental areas, Ukraine is now participating in the LHC project (LHC - Large Hadron Collider) and in CERN" (we will officially become a member only after paying the entrance fee) ", - Bogdan Gnatyk, Doctor of Physical and Mathematical Sciences, told LIGA.net.
According to him, since 2015 Ukraine has been a full member of the international collaboration CTA (MChT-Cherenkov Telescope Array), which is building a modern telescope multi TeV wide 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 new electromagnetic field promises us many more discoveries in the future,” adds the scientist.
What's next and how new knowledge will help people? Scholars disagree. Some say that this is just another 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 discovery once again proved how little we understand and how much remains to be learned.
The key difference is that while sound needs a medium in which to travel, gravitational waves move the medium—in this case, spacetime itself. “They literally crush and stretch the fabric of spacetime,” says Chiara Mingarelli, a gravitational wave astrophysicist at Caltech. To our ears, the waves detected by LIGO will sound like a gurgle.
How exactly will this revolution take place? LIGO currently has two detectors that act as "ears" for scientists, and there will be more detectors in the future. And if LIGO was the first to discover, it certainly won't be the only one. There are many types of gravitational waves. In fact, there is a whole spectrum of them, just like there are different types of light, with different wavelengths, in the electromagnetic spectrum. Therefore, other collaborations will start hunting for waves with a frequency that LIGO is not designed for.
Mingarelli works with the NanoGRAV (North American Nanohertz Gravitational Wave Observatory) collaboration, part of a major international consortium that includes the European Pulsar Timing Array and the Parkes Pulsar Timing Array in Australia. As the name suggests, NanoGRAV scientists hunt low-frequency gravitational waves in the 1 to 10 nanohertz mode; LIGO's sensitivity is in the kilohertz (audible) part of the spectrum, looking for very long wavelengths. 
This collaboration is based on pulsar data collected by the Arecibo Observatory in Puerto Rico and the Green Bank Telescope in West Virginia. Pulsars are rapidly rotating neutron stars that form when stars more massive than the Sun explode and collapse into themselves. They spin faster and faster as they are compressed, much like a weight at the end of a rope spins faster the shorter the rope gets.
They also emit powerful bursts of radiation as they rotate, like a beacon, which are recorded as pulses of light on Earth. And this periodic rotation is extremely precise - almost as accurate as an atomic clock. It makes them ideal cosmic gravitational wave detectors. The first indirect evidence came from studying pulsars in 1974, when Joseph Taylor Jr. and Russell Hulse discovered that a pulsar orbiting a neutron star slowly shrinks with time—an effect that would be expected if it were to convert some of its mass into energy in the form of gravitational waves.
In the case of NanoGRAV, the smoking gun will have a kind of flicker. The impulses should arrive at the same time, but if a gravitational wave hits them, they will arrive a little earlier or later, since space-time will contract or stretch as the wave passes.
Pulsar time-grid arrays are especially sensitive to gravitational waves produced by the merging of supermassive black holes a billion or ten billion times the mass of our Sun, like those that lurk at the center of the most massive galaxies. If two such galaxies merge, the holes in their centers will also merge and emit gravitational waves. “LIGO sees the very end of the merger when the pairs are very close,” says Mingarelli. “With the help of the SDM, we could see them at the beginning of the spiral phase, when they are just entering each other’s orbit.”
And there is also the LISA (Laser Interferometer Space Antenna) space mission. Earth-based LIGO is excellent at detecting gravitational waves, the equivalent of a fraction of the spectrum of audible sound, like what our merging black holes have produced. But many interesting sources of these waves produce low frequencies. So physicists have to go into space to find them. The main task of the current LISA Pathfinder () mission is to test the operation of the detector. “With LIGO, you can stop the tool, open the vacuum, and fix everything,” says MIT's Scott Hughes. But you can't open anything in space. You have to do it right away to make it work.”
The goal of LISA is simple: using laser interferometers, the spacecraft will attempt to accurately measure the relative position of two 1.8-inch gold-platinum cubes in free fall. Housed in separate electrode boxes 15 inches apart, the test objects will be shielded from the solar wind and other outside forces, so it will be possible to detect tiny motion caused by gravitational waves (hopefully).
Finally, there are two experiments designed to search for fingerprints left by primordial gravitational waves in the CMB (the afterglow of the Big Bang): BICEP2 and the Planck satellite mission. BICEP2 claimed to have detected one in 2014, but it turned out that the signal was fake (cosmic dust was to blame).
Both collaborations continue to hunt in hopes of shedding light on the early history of our universe - and hopefully confirming inflationary theory's key predictions. This theory predicted that shortly after its birth, the universe experienced a rapid growth, which could not but leave powerful gravitational waves, which remained imprinted in the background radiation in the form of special light waves (polarization).
Each of the four gravitational wave regimes will open four new windows on the universe to astronomers.
But we know what you're thinking: it's time to fire up the warp drive, dudes! Will the LIGO discovery help build the Death Star next week? Of course not. But the better we understand gravity, the more we will understand how to build these things. After all, this is the work of scientists, this is how they earn their bread. By understanding how the universe works, we can rely more on our capabilities.
On February 11, 2016, an international group of scientists, including from Russia, at a press conference in Washington announced a discovery that will sooner or later 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 its practical application. But they remind that until quite recently, humanity also did not know exactly what to do with electromagnetic waves, which eventually led to a real scientific and technological revolution.
What are gravitational waves in simple terms
Gravity and universal gravitation are one and the same. Gravitational waves are one of the OTS solutions. They must propagate 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 radiates energy on the order of several kilowatts in gravitational waves. This is a tiny amount, comparable to 3 old color TVs.
Another thing is two pulsars (neutron stars) rotating around each other. They move in very tight orbits. Such a "couple" was discovered by astrophysicists and has been observed for a long time. The objects were ready to fall on each other, which indirectly indicated that pulsars radiate space-time waves, that is, energy in their field.
Gravity is the force of attraction. We are drawn to the ground. And the essence of a gravitational wave is a change in this field, extremely weak when it comes to us. For example, take the level of water in a reservoir. The intensity of the gravitational field is the acceleration of free fall at a particular point. A wave is running across our reservoir, and suddenly the acceleration of free fall changes, just a little bit.
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 were waiting for a wave from a collision of, for example, two massive black holes to suddenly reach us. The researchers were enthusiastic and said that the entire globe could be affected by a gravitational wave coming from outer space. The planet will begin to oscillate and these seismic waves (compressional, shear and surface) can be studied.
An important article about the device in plain language, and how the Americans and LIGO stole the idea of the Soviet scientists and built the introferometers that allowed the discovery. Nobody talks about it, everyone is silent!
By the way, gravitational radiation is more interesting from the standpoint of relic radiation, which they try to find by changing the spectrum of electromagnetic radiation. Relic and electromagnetic radiation appeared 700 thousand years after the Big Bang, then in the process of expanding the universe filled with hot gas with traveling shock waves, which later turned into galaxies. In this case, of course, a gigantic, breathtaking 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. Domestic 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 starts to oscillate. And even the smallest 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. Do not be lazy, find an article by Soviet scientists in 1962.
First, the mirror must be massive in order to feel the "ripples". Secondly, it must be cooled to almost absolute zero (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 an elementary particle - the carrier of gravitational waves:
What are gravitational waves?
Gravitational waves - changes in the gravitational field, propagating like waves. They are radiated by moving masses, but after radiation they break away from them and exist independently of these masses. Mathematically related to the perturbation of the spacetime metric and can be described as "spacetime ripples".
In the general theory of relativity and in most other modern theories of gravity, gravitational waves are generated by the movement 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). They were first directly detected in September 2015 by two twin detectors at the LIGO observatory, which registered gravitational waves, probably as a result of the merger of two black holes and the formation of one more massive rotating black hole. Indirect evidence of their existence has been known since the 1970s - general relativity predicts the rate of convergence of close systems of binary stars that coincides with observations due to the loss of energy for 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.
If we imagine our space-time as a grid of coordinates, then gravitational waves are perturbations, ripples that will run along the grid when massive bodies (for example, black holes) distort the space around them.
It can be compared to an earthquake. Imagine that you live in a city. It has some markers that create an urban space: houses, trees, and so on. They are motionless. When a large earthquake occurs somewhere near the city, vibrations reach us - and even motionless houses and trees begin to oscillate. These fluctuations are gravitational waves; and the objects that oscillate are space and time.
Why did scientists take so long to detect gravitational waves?
Specific efforts to detect gravitational waves began in the post-war period with somewhat naive devices, the sensitivity of which, obviously, could not be sufficient to detect such oscillations. Over time, it became clear that the detectors for the search should be very large - and they should use modern laser technology. It is with the development of modern laser technologies that it became possible to control the geometry, the perturbations of which are the gravitational wave. The most powerful development of technology played a key role in this discovery. No matter how brilliant the scientists were, 30-40 years ago it was technically simply impossible to do this.
Why is wave detection so important to physics?
Gravitational waves were predicted by Albert Einstein in his general theory of relativity about a hundred years ago. Throughout the 20th century, there were physicists who questioned this theory, although more and more confirmations appeared. And the presence of gravitational waves is such a critical confirmation of the theory.
In addition, before the registration of gravitational waves, we knew how gravity behaves only on the example of celestial mechanics, the interaction of celestial bodies. But it was clear that the gravitational field has waves and space-time can be deformed in a similar way. The fact that we had not seen gravitational waves before was a blank spot in modern physics. Now this white spot has been closed, another brick has been laid at the foundation of modern physical theory. This is a fundamental discovery. There has been nothing comparable in recent years.
"Waiting for Waves and Particles" - a documentary about the search for gravitational waves(by Dmitry Zavilgelskiy)
There is a practical moment in the registration of gravitational waves. Probably, after the further development of technology, it will be possible to talk about gravitational astronomy - about observing traces of the most high-energy events in the Universe. But now it is too early to talk about it, we are talking only about the very fact of registering waves, and not about clarifying the characteristics of the objects that generate these waves.
Astrophysicists have confirmed the existence of gravitational waves, the existence of which was predicted by Albert Einstein about 100 years ago. They were recorded using detectors of the LIGO gravitational wave observatory, which is located in the United States.
For the first time in history, humanity has recorded gravitational waves - fluctuations in space-time that came to Earth from a collision of two black holes that occurred far in the Universe. Russian scientists also contribute to this discovery. On Thursday, researchers talk about their discovery around the world - in Washington, London, Paris, Berlin and other cities, including Moscow.
The photo shows an imitation of the collision of black holes
At a press conference in the office of Rambler & Co, Valery Mitrofanov, the head of the Russian part of the LIGO collaboration, announced the discovery of gravitational waves:
“We are honored to participate in this project and present the results to you. I will now tell you the meaning of the discovery in Russian. We have seen beautiful pictures of LIGO detectors in the US. The distance between them is 3000 km. Under the influence of a gravitational wave, one of the detectors shifted, after which we discovered them. At first, we saw just noise on the computer, and then the buildup of the mass of the Hamford detectors began. After calculating the data obtained, we were able to determine that it was the black holes that collided at a distance of 1.3 mlrd. light years from here. The signal was very clear, he got out of the noise very clearly. Many told us that we were lucky, but nature gave us such a gift. Gravitational waves have been discovered - that's for sure."
Astrophysicists have confirmed rumors that using the detectors of the gravitational wave observatory LIGO they were able to detect gravitational waves. This discovery will allow humanity to make significant progress in understanding how the universe works.
The discovery took place on September 14, 2015, simultaneously by two detectors in Washington and Louisiana. The signal arrived at the detectors as a result of the collision of two black holes. So much time it took scientists to make sure that it was gravitational waves that were the product of the collision.
The collision of holes occurred at a speed of about half the speed of light, which is approximately 150,792,458 m/s.
“Newtonian gravity was described in flat space, and Einstein translated it into the plane of time and suggested that it bends it. The gravitational interaction is very weak. On Earth, the experience of creating gravitational waves is impossible. They were able to detect them only after the merger of black holes. The detector has shifted, just imagine, by 10 to -19 meters. Don't touch it with your hands. Only with the help of very precise instruments. How to do it? The laser beam with which the shift was detected is unique in nature. The second-generation LIGO laser gravity antenna went into operation in 2015. The sensitivity makes it possible to register gravitational perturbations about once a month. This is the advanced world and American science, there is nothing more accurate in the world. We hope that it will be able to overcome the Standard quantum limit of sensitivity, ”explained the discovery. Sergey Vyatchanin, an employee of the Faculty of Physics of Moscow State University and the LIGO collaboration.
The standard quantum limit (SQL) in quantum mechanics is a limitation imposed on the accuracy of a continuous or many times repeated measurement of a quantity described by an operator that does not commute with itself at different times. Predicted in 1967 by V. B. Braginsky, and the term Standard Quantum Limit (SQL) was proposed later by Thorne. The SQL is closely related to the Heisenberg uncertainty relation.
Summing up, Valery Mitrofanov spoke about plans for further research:
“This discovery is the beginning of a new gravitational wave astronomy. Through the channel of gravitational waves, we expect to learn more about the Universe. We know the composition of only 5% of matter, the rest is a mystery. Gravitational detectors will allow you to see the sky in "gravitational waves". In the future, we hope to see the beginning of everything, that is, the cosmic microwave background of the Big Bang, and understand what exactly happened then.”
For the first time, gravitational waves were proposed by Albert Einstein in 1916, that is, almost exactly 100 years ago. The equation for waves is a consequence of the equations of the theory of relativity and is not derived in the simplest way.
Canadian theoretical physicist Clifford Burgess previously published a letter saying that the observatory had 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. The collision and the asymmetric gravitational collapse last for a fraction of a second, and during this time, up to 50 percent of the mass of the system goes into gravitational radiation - the ripples of space-time.
A gravitational wave is a gravitational wave generated in most theories of gravity by the movement of gravitating bodies with variable acceleration. In view of the relative weakness of gravitational forces (compared to others), these waves should have a very small magnitude, which is difficult to register. Their existence was predicted about a century ago by Albert Einstein.
