Merger of two neutron stars. For the first time, gravitational waves from the merger of two neutron stars have been detected. What does all of this mean

Immediately in all ranges of the spectrum, a plus is to register gravitational waves from this event. A photograph taken by the Hubble Telescope shows the galaxy NGC 4993 in which this happened. The yellow spot above and to the left of the galaxy's center is a flare from the merger. The insets show how it changed from August 22 to August 28.

The gravitational wave burst itself occurred on August 17 of this year, and therefore received the name GW170817. At first it was caught by VIRGO (the installation successfully connected for a short time to the LIGO scientific observation session), and then - a split second later - by American detectors. The observed burst lasted almost two minutes! It's worth a listen!

But most importantly, after 1.7 seconds, gamma detectors on the Fermi and INTEGRAL satellites registered a short gamma-ray burst, named GRB 170817A. As it quickly became clear, these are related events.

Gravitational detectors cannot very accurately determine the point of the burst in the sky, even in this case, when three detectors were activated, the area of ​​uncertainty was about 30 square degrees (more than 100 lunar disks), but gamma detectors can determine the coordinates much more accurately. Therefore, it was immediately possible to connect observers working in the entire range of the spectrum (in addition, data from neutrino detectors were analyzed, but they did not see anything, as, indeed, was expected). And this led to an amazing discovery - the burst and its afterglow could be seen in the X-ray, optical, ultraviolet, and infrared ranges!

Since the gravitational wave signal and the gamma-ray burst arrived almost simultaneously, we can state with high accuracy (approximately 10 −15) that the speed of propagation of gravitational waves is equal to the speed of light (note that the delay is most likely due not to the difference in speeds, but to the physics of generation gamma-ray burst). In addition, it was possible to verify several more predictions of the General Theory of Relativity with higher accuracy than before.

The presence of a gravitational wave signal allows one to directly determine the distance to the merging objects. And optical measurement data provides identification of the galaxy, that is, it allows one to determine the red shift. Together, these independent measurements allow the Hubble constant to be determined. So far, however, they are not very accurate - 60–80 (km/s)/Mpc. This accuracy is worse than in a number of other cosmological measurements. However, it is important that in this case the Hubble constant is measured by a completely different independent method, moreover, model-independent (that is, there is no need to lay down additional theoretical assumptions to obtain the result). Therefore, we can hope that in the future, similar data on the observation of neutron star mergers using gravitational wave detectors in galaxies with a known redshift will become a source of significant cosmological information.

So. At a distance of 130 million light years (40 megaparsecs), two neutron stars merged in the galaxy NGC 4993. As a result, a gravitational wave burst occurred, and a large amount of energy was released in different ranges of the electromagnetic spectrum.

In addition to the main flare, for some time astronomers have also observed the so-called kilonova (they are sometimes also called macronovas, see Kilonova). This radiation is associated with the decay of radioactive elements synthesized as a result of the merger of neutron stars. The synthesis occurs as a result of the so-called r-process, the letter “r” here comes from the word rapid (fast). After the merger, the expanding matter is penetrated by a flux of neutrons and neutrinos. This creates favorable conditions for the transformation of element nuclei into heavier ones. The nuclei capture neutrons, which can then turn into protons inside the nucleus, causing the nucleus to jump one cell on the periodic table. So you can “jump” not only to lead, but also to uranium and thorium. Modern calculations show that the bulk of heavy elements (with a mass of more than 140), for example, gold and platinum, are synthesized precisely as a result of the merger of neutron stars, and not during supernova explosions.

Thus, a large complex of data was obtained from one event, interesting for a wide variety of areas of physics and astrophysics:

1. The connection between short gamma-ray bursts and neutron star mergers has been proven. The new data will provide a much better understanding of the physics of short gamma-ray bursts.
2. It was possible to conduct an excellent test of a number of predictions of General Relativity (speed of propagation of gravitational waves, Lorentz invariance, equivalence principle).
3. Unique data on the synthesis of elements during the merger of neutron stars were obtained.
4. It was possible to obtain a direct measurement of the Hubble constant

We expect that subsequent observations will help us determine with high accuracy the masses and radii of neutron stars (which is important for understanding their structure, that is, relevant for nuclear physics), and we also expect an event where the merger of two neutron stars will lead to the observed formation of a black hole. By the way, it is impossible to say exactly what happened as a result of this event (but most likely, a black hole was formed).

In conclusion, we note that astronomers are very, very lucky. First of all, the splash is very close. Secondly, the probability that a gravitational wave burst will be accompanied by a gamma-ray burst is not very high. Let's hope astronomers continue to have better luck!

Original articles with materials related to the discovery can be found on the LIGO website.

Sergey Popov

For the first time in human history, astronomers have detected gravitational waves from the merger of two neutron stars. The event in the galaxy NGC 4993 was “sensed” on August 17 by the LIGO/Virgo gravitational observatories. Following them, other astronomical instruments joined in the observations. As a result, 70 observatories observed the event, and according to observational data, at least 20 (!) scientific articles were published today.

Rumors that the LIGO/Virgo detectors have finally registered a new event and this is not another black hole merger began to spread across social networks on August 18. A statement about it was expected at the end of September, but then scientists limited themselves to only the next gravitational wave event involving two black holes - it occurred 1.8 billion light years from Earth, and for the first time not only American detectors took part in its observation on August 14, but also the European Virgo, which “joined” the hunt for space-time fluctuations two weeks earlier.

New LIGO. Source with optical counterpart. Blow your sox off!

J Craig Wheeler (@ast309) August 18, 2017

After this, the collaboration won its well-deserved Nobel Prize in physics - for the detection of gravitational waves and confirmation of Einstein’s correctness in predicting their existence - and now it has told the world about the discovery that it saved for “sweets”.

What exactly happened?

Neutron stars are very, very small and very dense objects that are usually created by supernova explosions. The typical diameter of such a star is 10-20 km, and the mass is comparable to the mass of the Sun (whose diameter is 100,000,000 times larger), so the density of the neutron star’s substance is several times higher than the density of the atomic nucleus. At the moment, we know of several thousand such objects, but there are only one and a half to two dozen binary systems.

A kilonova (similar to a “supernova”), the gravitational effect of which was recorded by LIGO/Virgo on August 17, is located in the constellation Hydra at a distance of 130 million light years from Earth. It resulted from the merger of two neutron stars with masses ranging from 1.1 to 1.6 solar masses. An indication of how close this event was to us is that while the signal from merging binary black holes was typically within the sensitivity range of LIGO detectors for a fraction of a second, the signal recorded on August 17 lasted about 100 seconds.

“This is not the first registered kilonova,” said astrophysicist Sergei Popov, leading researcher at the State Astronomical Institute. PC. Sternberg - but they could be listed not even on the fingers of one hand, but almost on the ears. There were literally one or two of them.”

Almost at the same time, about two seconds after the gravitational waves, NASA's Fermi Gamma-Ray Space Telescope and INTERnational Gamma-Ray Astrophysics Laboratory/INTEGRAL detected gamma-ray bursts. In the following days, scientists recorded electromagnetic radiation in other ranges, including X-ray, ultraviolet, optical, infrared and radio waves.

Having received the coordinates, several observatories were able to begin searching within a few hours in the area of ​​​​the sky where the event supposedly occurred. The new bright point, resembling a nova, was detected by optical telescopes, and about 70 observatories eventually observed the event in various wavelength ranges.

“For the first time, in contrast to “lonely” black hole mergers, a “company” event was recorded not only by gravitational detectors, but also by optical and neutrino telescopes. This is the first such round dance of observations around one event,” said Professor of the Faculty of Physics of Moscow State University Sergei Vyatchanin, who is part of a group of Russian scientists who participated in the observation of the phenomenon under the leadership of Professor of the Faculty of Physics of Moscow State University Valery Mitrofanov.

At the moment of the collision, the main part of the two neutron stars merged into one ultra-dense object emitting gamma rays. The first measurements of gamma rays, combined with the detection of gravitational waves, confirm the prediction of Einstein's general theory of relativity, namely that gravitational waves travel at the speed of light.

“In all previous cases, the source of gravitational waves was merging black holes. Paradoxically, black holes are very simple objects, consisting entirely of curved space and therefore completely described by the well-known laws of general relativity. At the same time, the structure of neutron stars and, in particular, the equation of state of neutron matter is still precisely unknown. Therefore, studying signals from merging neutron stars will allow us to obtain a huge amount of new information also about the properties of superdense matter under extreme conditions,” said Farit Khalili, a professor at the Faculty of Physics at Moscow State University, who is also part of Mitrofanov’s group.

What is the significance of this discovery?

First, observing neutron star mergers is another clear demonstration of the power of astronomical observations pioneered by the LIGO and Virgo detectors.

“This is the birth of a new science! Today is such a day,” Vladimir Lipunov, head of the space monitoring laboratory of the State Aviation Institute of Moscow State University and head of the MASTER project, told Cherdak. - It will be called gravitational astronomy. This is when all the thousand-year-old methods of astronomy, which thousands of astronomers have used for many thousands of years, have developed, will become useful for gravitational wave topics. Until today, all this was pure physics, that is, even fantasy from the point of view of the public, but now it is already a reality. New reality."

“A year and a half ago, when gravitational waves were discovered, a new way of studying the Universe, studying the nature of the Universe was discovered. And this new method has already demonstrated in a year and a half its ability to give us important, deep information about various phenomena in the Universe. For several decades, they were just trying to detect gravitational waves, and then once - a year and a half ago they were detected, received the Nobel Prize, and now a year and a half has passed, and it has really been shown that, except for the flag that everyone raised - yeah, Einstein was right! “It’s really working now, only at the beginning of the science of gravitational astronomy, it turns out to be so effective to study various phenomena in the Universe,” astrophysicist Yuri Kovalev, head of the laboratory for fundamental and applied research of relativistic objects of the Universe at MIPT, head of the laboratory, told the Attic correspondent Lebedev Physical Institute, head of the scientific program of the Radioastron project.

In addition, during the observations a huge amount of new data was collected. In particular, it was recorded that during the merger of neutron stars, heavy elements such as gold, platinum and uranium are formed. This confirms one of the existing theories of the origin of heavy elements in the Universe. Previous modeling had already demonstrated that supernova explosions alone are not enough to synthesize heavy elements in the Universe, and in 1999 a group of Swiss scientists suggested that neutron star mergers could be another source of heavy elements. Although kilonovae are much rarer than supernovae, they can generate most of the heavy elements.

“Imagine, you’ve never found money on the street, and then you finally found it. And this is a thousand dollars at once,” says Sergei Popov. - Firstly, this is confirmation that gravitational waves propagate at the speed of light, confirmation with an accuracy of 10 -15. This is a very important thing. Secondly, this is a certain number of purely technical confirmations of a number of provisions of the general theory of relativity, which is very important for fundamental physics in general. Thirdly - if we return to astrophysics - this is confirmation that short gamma-ray bursts are the merger of neutron stars. As for heavy elements, of course, it’s not that no one believed in this before. But there wasn’t such a gorgeous set of data.”

And this complex of data already on the first day allowed scientists to publish, according to Attic calculations, at least 20 articles (eight in Science, five in Nature, two in Physical Review Letters and five in Astrophysical Journal Letters). According to journalists' estimates Science, the number of authors of the article describing the event roughly corresponds to a third of all active astronomers. Are you looking forward to the continuation? We do.

Yesterday, at a press conference in Washington, scientists officially announced the registration of an astronomical event that no one had recorded before - the merger of two neutron stars. Based on the results of the observation, more than 30 scientific articles were published in five journals, so we cannot talk about everything at once. Here is a summary and the most important discoveries.
Astronomers have observed the merger of two neutron stars and the birth of a new black hole. Neutron stars are objects that appear as a result of explosions of large and massive (several times heavier than the Sun) stars. Their sizes are small (they are usually no more than 20 kilometers in diameter), but their density and mass are enormous. The merger of two neutron stars created a black hole 130 million light-years from Earth, an object even more massive and dense than the neutron star. The merger of stars and the formation of a black hole was accompanied by the release of enormous energy in the form of gravitational, gamma-ray and optical radiation. All three types of radiation were recorded by terrestrial and orbital telescopes. The gravitational wave was recorded by the LIGO and VIRGO observatories.
This gravitational wave was the highest energy wave observed so far. All types of radiation reached the Earth on August 17. First, ground-based laser interferometers LIGO and Virgo recorded the periodic compression and expansion of space-time - a gravitational wave that circled the globe several times. The event that generated the gravitational wave was named GRB170817A. A few seconds later, NASA's Fermi Gamma-ray Telescope detected high-energy photons in the gamma-ray range. And then something began: having received a warning from the LIGO/Virgo collaboration, astronomers all over the Earth adjusted their telescopes to the coordinates of the radiation source. On this day, large and small, ground-based and orbital telescopes operating in all ranges looked at one point in space. Based on the results of observations, the University of California (Berkeley) made a computer simulation of the merger of neutron stars. Both stars appeared to have a mass slightly larger than the Sun (but a much smaller radius). These two balls of incredible density swirled around each other, constantly accelerating. Here's how it went: As a result of the merger of neutron stars, atoms of heavy elements - gold, uranium, platinum - were released into outer space; astronomers believe that such events are the main source of these elements in the universe. Optical telescopes first “saw” blue visible light, and then ultraviolet radiation, which gave way to red light and radiation in the infrared range.
This sequence matches theoretical predictions. According to the theory, when neutron stars collide, they lose some of their matter - it is sprayed around the collision site with a huge cloud of neutrons and protons. When a black hole begins to form, an accretion disk forms around it, in which particles spin at enormous speeds - so great that some overcome the black hole's gravity and fly away. This fate awaits approximately 2% of the matter of colliding stars. This substance forms a cloud around the black hole with a diameter of tens of thousands of kilometers and a density approximately equal to that of the Sun. The protons and neutrons that make up this cloud stick together to form atomic nuclei. Then the decay of these nuclei begins. Astronomers on Earth observed the radiation from decaying nuclei for several days. In the millions of years since the GRB170817A event, this radiation has filled the entire galaxy.

Today, at a press conference in Washington, scientists officially announced the registration of an astronomical event that no one had recorded before - the merger of two neutron stars. Based on the results of the observation, more than 30 scientific articles were published in five journals, so we cannot talk about everything at once. Here is a summary and the most important discoveries.

Astronomers have observed the merger of two neutron stars and the birth of a new black hole.

Neutron stars are objects that appear as a result of explosions of large and massive (several times heavier than the Sun) stars. Their sizes are small (they are usually no more than 20 kilometers in diameter), but their density and mass are enormous.

The merger of two neutron stars created a black hole 130 million light-years from Earth—an object even more massive and dense than the neutron star. The merger of stars and the formation of a black hole was accompanied by the release of enormous energy in the form of gravitational, gamma-ray and optical radiation. All three types of radiation were recorded by terrestrial and orbital telescopes. The gravitational wave was recorded by the LIGO and VIRGO observatories.

This gravitational wave was the highest energy wave observed so far.

All types of radiation reached the Earth on August 17. First, ground-based laser interferometers LIGO and Virgo recorded the periodic compression and expansion of space-time - a gravitational wave that circled the globe several times. The event that generated the gravitational wave was named GRB170817A. A few seconds later, NASA's Fermi Gamma-ray Telescope detected high-energy photons in the gamma-ray range.

On this day, large and small, ground-based and orbital telescopes operating in all ranges looked at one point in space.

Based on the results of observations, the University of California (Berkeley) made a computer simulation of the merger of neutron stars. Both stars appeared to have a mass slightly larger than the Sun (but a much smaller radius). These two balls of incredible density swirled around each other, constantly accelerating. Here's how it went:

As a result of the merger of neutron stars, atoms of heavy elements - gold, uranium, platinum - were released into outer space; astronomers believe that such events are the main source of these elements in the universe. Optical telescopes first “saw” blue visible light, and then ultraviolet radiation, which gave way to red light and radiation in the infrared range.

This sequence matches theoretical predictions. According to the theory, when neutron stars collide, they lose some of their matter - it is sprayed around the collision site with a huge cloud of neutrons and protons. When a black hole begins to form, an accretion disk forms around it, in which particles spin at enormous speeds—so great that some overcome the black hole's gravity and fly away.

This fate awaits approximately 2% of the matter of colliding stars. This substance forms a cloud around the black hole with a diameter of tens of thousands of kilometers and a density approximately equal to that of the Sun. The protons and neutrons that make up this cloud stick together to form atomic nuclei. Then the decay of these nuclei begins. Astronomers on Earth observed the radiation from decaying nuclei for several days. In the millions of years since the GRB170817A event, this radiation has filled the entire galaxy.