The biggest intrigue of the anticipated announcement of the first gravitational wave registration was the question of whether its tracks were found in the electromagnetic range. According to the widespread theory, gamma-ray bursts are the result of the merger of neutron stars and black holes. According to the first reports, it turned out that no traces of the source of gravitational waves were found in the electromagnetic spectrum. However, now there is information that this is still not the case. Sergey Popov accidentally found a preprint of a publication about the registration of an event in gamma rays by the space observatory Fermi.
This discovery is very significant from a scientific point of view. It could prove for the first time that short GRBs are the result of black hole mergers. Such mergers should be one of several main types of mergers of astronomical objects that occur during The universe... Let's list their main types:
1) Mergers of ordinary stars
About half of the stars in our galaxy are part of binary or more numerous systems. Some of them are in very close orbits. Sooner or later, some stars must merge into one star, due to deceleration in each other's extended envelopes. Such events have already been observed.
September 2, 2008 in the constellation Scorpion flashed bright New... She received the designation New Scorpio 2008... This star at its maximum reached the 7th magnitude and at first seemed ordinary New... But then the study of archival photometry dramatically changed the opinion of scientists about this star. Since the outbreak occurred on the dense stellar fields of the galaxy, it came into the field of view of the project OGLEon the search for microlens events. As a result of studying many thousands of images of this project, it turned out that the star increased its brightness not abruptly, but smoothly, over several tens of days:
In general, it was possible to trace the changes in the brightness of the star, starting in 2001:
Examining this data revealed an even more surprising detail. It turned out that the star shows periodic changes in brightness - with a period equal to about one day. In addition, it turned out that the period of these fluctuations rapidly decreased over time:
After the outbreak, an attempt was made to find a similar frequency. It ended in failure. Therefore, it was concluded that the only realistic scenario to explain what happened is the hypothesis merge of two stars into one.
2) White dwarf mergers
Any star dies sooner or later. If its mass is less than 1.4 mass Suns, then it becomes a white dwarf through the red giant stage. Such stars should also form binary systems. First, in 1967, close systems of the type AM Hounds Dogs , in which there was only one white dwarf. Twenty years later, a double white dwarf was discovered with an orbital period of only 1.5 days. Gradually, astronomers discovered more and more closely similar systems. In 1998, a white dwarf system was discovered with an orbital period of only 39 minutes. The stars in it are expected to merge into one in 37 million years.
Scientists are considering two options for the consequences of the merger of such stars. An ordinary star appears on the first of them, an explosion occurs on the second. type 1 supernova... Unfortunately, it is not yet possible to test any of these versions. Even the brightest supernovae observed today are found in distant galaxies. Therefore, even in the best cases, only a faintly visible star can be seen in the place of supernovae.
3) Mergers of neutron stars and black holes of stellar masses
If the mass of the star significantly exceeds the threshold of 1.4 masses Suns, then she ends her life no longer with the harmless stage of the red giant, but with a super-powerful supernova explosion. If the star does not greatly exceed this threshold, then a neutron star is formed - an object only a few kilometers in size. In the case of multiple exceeding the threshold, a black hole is formed - an object whose second cosmic speed exceeds the speed of light.
The existence of neutron stars and black holes was predicted by theorists decades before their discovery. Do they form binary systems? In theory, this might seem unlikely, since a supernova explosion is characterized by a large loss of mass and, therefore, the binary system should be destabilized. However, just 7 years after the discovery of the first pulsar (neutron star), the first binary system of neutron stars was discovered. Her discovery turned out to be so significant that they gave for her Nobel Prize(a decrease in the period of the system was found, consistent with losses due to gravitational radiation). In 2003, the first binary pulsar was discovered with an orbital period of 2.4 hours. In 85 million years, both neutron stars are expected to merge into one.
Simultaneously with the discovery of pulsars, mysterious gamma-ray bursts... At first, they could not be detected in other ranges of electromagnetic radiation. This made it impossible to estimate even the order of the distance to them. It was only in 1997 that the optical afterglow of a gamma-ray burst was detected for the first time and its redshift was measured. It turned out to be huge, many times the distance to the most distant supernovae. Hence the conclusion about the enormous power of such explosions followed:
At the beginning of May 1998, more precisely on the evening of May 6, a press release from NASA was distributed in the United States and via electronic channels (Internet), which reported on the measurement by a team of American and Italian astronomers at the 10-m telescope. Keck (USA) redshift of a faint galaxy, which is visible at the site of the GRB 971214 gamma-ray burst, recorded by the Italian-Dutch satellite BeppoSAX on December 12, 1997. Official scientific information appeared in the form of a series of articles in the issue of the journal "Nature" on May 7, 1998. (Kulkarni SR et al., Nature, 393, 35; Halpern et al., Nature, 393, 41; Ramaprakash AN et al., Nature, 393, 43). The redshift in the spectrum of this galaxy turned out to be extremely large, z \u003d 3.418, i.e. light from it was emitted at a time when the age of the universe was only 1/7 of modern meaning (12 billion years). The photometric distance to this galaxy is determined by the redshift and is equal to 10 ^ 28 cm. Then, based on the illumination of gamma radiation from this burst measured on Earth (10-5 erg cm-2 in the energy range\u003e 20 keV), it is possible to restore the total energy release: in the gamma range alone, it turned out to be incredibly large, 10 ^ 53 erg. This energy is 20% of the energy of the rest mass of the Sun and is 50 times greater than all the energy that has been emitted by the Sun during its entire existence. And all this - in those 30 seconds that the gamma-ray burst lasted! The peak luminosity (energy release) within a few hundredths of a second was 10 ^ 55 erg / s, which corresponds to the electromagnetic luminosity of half of all stars in the Universe. An amazing phenomenon, isn't it? To further intrigue the reader, the authors estimate the maximum energy density near the place of this energy release and show that it is comparable to that which took place in the hot Universe 1 s after the beginning of expansion ("Big Bang"), in the era of primary nucleosynthesis.
Among theorists, the opinion about the sources of such a powerful source of energy was almost unanimous:
So, firmly taking the position of the cosmological nature of gamma-ray bursts, an explanation is required for such a high energy release in the form of electromagnetic radiation, the shape and temporal behavior of the spectra of gamma-ray bursts themselves and their X-ray, optical and radio twins, frequencies of origin, etc. As mentioned above, the merger of two compact stars (neutron stars or black holes) undividedly claimed the role of a source of energy for gamma-ray bursts. The details of this model are extremely poorly understood due to the complexity of the physical processes in such an event. We repeat, the main argument boiled down to the sufficiency of the potentially released energy (10 ^ 53 erg), a sufficient frequency of events (on average, about 10 ^ -4 - 10 ^ -5 per year per galaxy) and the actual observation of at least 4 double neutron stars in the form binary radio pulsars, in which the invisible star has a mass of about 1.4 solar masses (the typical mass of a neutron star) and is extremely compact.
However, until now, these were only assumptions, supplemented by the discovery of some indirect signs. Everything changes with a recent publication. It follows from it that the device GBM (Gamma-ray Burst Monitor)satellite Fermi only 0.4 seconds after the registration of the gravitational wave, he observed a weak gamma-ray burst lasting one second. The signal fell on the same area as the source of the gravitational wave. Moreover, the detection of a gamma-ray burst allows you to narrow the area of \u200b\u200bthe event from 601 to 199 square degrees. The event looks statically valid ( SNR \u003d 5.1) due to the fact that the observation area of \u200b\u200bthe device GBMmakes up 70% of the area of \u200b\u200bthe sky.
Of course, one cannot be 100% sure of the correct interpretation of an event. So far, no reliable binary system of stellar mass black holes is known. Usually binaries with black holes are detected by X-rays. For the presence of such radiation, it is necessary that at least one of the participants in the binary system is an ordinary star - a donor of matter for the accretion disk.
The registration of a weak and short gamma-ray burst from the merger of black holes raises many questions about the origin of such electromagnetic radiation. As you know, the second cosmic speed of black holes exceeds the speed of light. Several options are possible:
A) Gamma radiation is caused by the absorption of the accretion disk of black holes or interstellar matter. The fact that the gamma-ray burst turned out to be weak suggests that bright and short gamma-ray bursts are generated by collisions of neutron stars, where there is more matter to be converted into gamma rays.
B) The radiation is caused by some unknown phenomenon, which nevertheless allows the matter in black holes to accelerate when merging to speeds higher than the speed of light (that is, to leave the black hole). An analogue of such radiation can be a hypothetical radiation Hawking .
It is obvious that the solution of this question can lead to tremendous progress in physics. In the coming years, as the sensitivity improves, gravitational detectors should increase their angular resolution and thereby simplify the identification of sources of gravitational waves with electromagnetic radiation.
4) Mergers of supermassive black holes
Since most theorists believe that nothing can leave a black hole (the second cosmic speed exceeds the speed of light), it is obvious that black holes must grow over time. In dense star clusters (such as globular clusters), they are expected to grow to several thousand masses. Suns, and in the central regions of galaxies they reach masses of several billion or even trillion masses Suns.
Some of these supermassive black holes are part of binary systems. And such systems have already been discovered. By now, not only double, but even triple and quadruple systems of supermassive black holes are known. Some of these systems are very tight. So in one of them, the period of rotation of black holes is five years. These black holes are expected to merge in less than a million years. In this case, energy should be released, which is a hundred million times higher than the energy of an ordinary supernova.
Such mergers will be the most powerful events in The universe... They should become the most powerful source of gravitational waves. It is possible that in the distant future, one of these mergers may cause a new Big bang and birth new universe ... Who knows, at least now in The universe only two phenomena are known that are characterized by the extreme density of matter - black hole and matter before Big bang.
Naturally, in addition to general cases, there should be special cases of large astronomical mergers, for example, the fall of planets on stars or the absorption of stars by supermassive black holes.
Such phenomena are also quite rare and occur at large distances, so many of their details are still unknown. Cognition The universe in the answer to one question always generates several more new questions.
The new model brings scientists closer to understanding the kind of light signals created when two supermassive black holes (millions and billions of times more massive than the Sun) spiral into collision. For the first time, computer modeling, including the physical effects of Einstein's general theory of relativity, shows that gas in such systems will glow mainly in UV and X-ray light.
Almost every galaxy with parameters Milky way contains a black hole in the center. Observations show that galactic mergers occur frequently, but until now no one has been able to see the process of colliding giant black holes. However, scientists were able to detect the merging of black holes of stellar mass (from three to several dozen solar masses) using LIGO. In this particular case, gravitational waves were created - ripples in space and time, moving at the speed of light.
Gas shines brightly in computer simulations of 40-orbit supermassive black holes from the merger. Models like these will help identify real-life examples of such binaries.
Mergers for supermassive black holes will be more difficult to identify. The fact is that the Earth itself is too noisy a place. It shakes from seismic vibrations and gravitational changes from atmospheric disturbances. Therefore, the detectors should be in space, as planned with LISA in the 2030s.
It is important to note that supermassive binaries will differ from their smaller counterparts in their gas-rich environment. Scientists suspect that the supernova explosion that forms the black hole also blows out most of the surrounding gas. The black hole is so quickly absorbed by the remnants that during the merger there is nothing left for "lunch" and no light signal occurs.
But let's not forget that the merger of supermassive black holes occurs against the background of a galactic merger, which means there is an accompaniment from clouds of gas and dust, stars and planets. Most likely, the galactic collision propels much of this material closer to the black holes, which continue to feed. As you get closer, magnetic and gravitational forces heat up the remaining gas, and astronomers can pick up signals.
The new simulation shows three orbits of a pair of supermassive black holes 40 orbits from the merger. It can be seen that at this stage of the process, light is emitted only in UV light using some high-energy X-rays.
This 360-degree vision takes us to the center of two rotating supermassive black holes 30 million km apart, with an orbital period of 46 minutes. Black holes can be seen distorting the stellar background and trapping light. Distinctive feature - photonic ring. The entire system will have 1 million solar masses
Three regions of light-emitting gas glow when black holes merge. This forms a large ring around the system as well as two smaller rings around each. All of these objects emit mainly UV rays. When the gas flows into the mini-drive on high speedThe UV light from the disk contacts each corona of black holes (a region of high-energy subatomic particles above and below the disk). When the accretion rate is lower, UV light dims relative to X-ray radiation.
Based on simulations, scientists expect X-rays created by "near-fusion" to be brighter than single supermassive black holes. For the simulation, a Blue Waters supercomputer was used for 46 days on 9600 computational cores. The original simulation estimates the gas temperature. The team plans to refine the code to simulate how system parameters such as temperature, distance, total mass, and accretion rate change. Scientists are interested in understanding what happens to gas traveling between two black holes.
When anything crosses the black hole event horizon from the outside, it is doomed. In a matter of seconds, the object will reach a singularity at the center of the black hole: a point for a non-rotating black hole and a ring for a rotating one. The black hole itself does not remember which particles fell into it or what their quantum state is. Instead, all that remains, in terms of information, is the total mass, charge, and angular momentum of the black hole.
In the final stage, preceding the merger, the spacetime surrounding the black hole will be disrupted as matter continues to fall into both black holes from environment... Under no circumstances should you assume that something can escape from within the event horizon.
Thus, one can imagine a scenario in which matter enters a black hole during the final stages of a merger, when one black hole is about to merge with another. Since black holes must always have accretion disks, and matter is constantly flying in the interstellar medium, particles will constantly cross the event horizon. Everything is simple here, so let's consider a particle that fell into the event horizon before the final moments of the merge.
Could she theoretically escape? Can you "jump" from one black hole to another? Let's look at the situation from the point of view of space-time.
Computer simulation of two merging black holes and the curvature of space-time caused by them. Although gravitational waves are emitted constantly, matter itself cannot escape
When two black holes merge, they do so after a long period of spiraling, during which energy is emitted in the form of gravitational waves. Until the very final moments before the merger, the energy is emitted and flies away. But this cannot cause the event horizon or even the black hole to contract; instead, energy comes from spacetime at the center of mass, which deforms more and more. You might as well steal energy from the planet; it would rotate closer to the Sun, but its properties (or the properties of the Sun) would not change in any way.
However, when the last moments of the merger arrive, the event horizons of the two black holes are deformed by the gravitational presence of each other. Fortunately, relativists have already numerically calculated how merging affects event horizons, and this is impressively informative.
Despite the fact that up to 5% of the total mass of black holes before merging can be emitted in the form of gravitational waves, the event horizon never contracts. The important thing is that if you take two black holes of equal mass, their event horizons will occupy a certain amount of space. When combined to create a double-mass black hole, the volume of space occupied by the horizon would be four times the original volume of the combined black holes. The mass of black holes is directly proportional to their radius, but the volume is proportional to the cube of the radius.
Although we have found many black holes, the radius of each event horizon is directly proportional to the mass of the hole, and this is always the case. Double the mass, double the radius, but the area will quadruple and the volume will quadruple.
It turns out that even if you keep the particle in the most motionless state inside the black hole and it falls as slowly as possible towards the singularity, there is no way for it to get out. The total volume of coincident event horizons increases during black hole mergers, and no matter what the trajectory of a particle crossing the event horizon is, it is doomed to be swallowed by the combined singularity of both black holes.
In many scenarios of astrophysics, ejections occur when matter escapes from an object during a cataclysm. But in the case of a merger of black holes, everything inside remains inside; most of what was outside is sucked in, and only a little of what was outside can escape. Falling into a black hole, you are doomed. And another black hole won't change the balance of power.
New computer simulations, which fully incorporate the physical effects of Einstein's General Theory of Relativity, show that gas in merging black hole systems emits predominantly in the ultraviolet and X-ray range. Research presented in the journal Astrophysical Journal .
“We know that galaxies with central supermassive black holes merge with each other, but only in a small part have we been able to detect the presence of two 'monsters'. And the pairs we see do not emit strong enough gravitational waves, since they are still too far apart. Our goal is to identify closer duos by light signals and thus track their gravitational waves in the future, ”says Scott Noble, an astrophysicist at NASA's Space Flight Center. Goddard (USA).
Supermassive black hole as seen by the artist. Credit: NASA
In 2015, scientists recorded the merging of stellar mass black holes using the LIGO observatory, but the collision of supermassive objects. One of the reasons ground-based observatories cannot detect the curvature of space-time from these events is that the Earth itself is subject to vibrations from seismic vibrations and changes. atmospheric pressureso the detectors must be in space, like the European Space Agency's (ESA) Laser Interferometer Space Antenna (LISA), slated to launch in the 2030s.
Comprehensive pulsar observations can also help detect gravitational waves from monster mergers. Like beacons, pulsars continuously emit synchronized beams of light. Gravitational waves should cause slight changes in flare periods, but this has not yet been observed in practice.
Image of the Sails pulsar from NASA's Chandra Observatory. Credit: NASA
Yet supermassive pairs approaching a collision have one thing that binary stellar mass systems do not: it is a gas-rich environment. Scientists speculate that a supernova explosion, creating a small black hole, blows away most of the surrounding gas, and the remaining gas falling on it is not enough for the powerful radiation during the merger.
On the other hand, pairs of supermassive black holes are the result of galaxies merging. Each of them is surrounded by clouds of gas and dust, stars and planets. The collision of galaxies propels most of the material towards the central black holes. As it approaches the event horizon, the remaining gas is heated by magnetic and gravitational forces and emits a bright glow observed by astronomers.
Simulating supermassive collisions requires sophisticated computational tools that account for all the physical effects created by two giant black holes orbiting each other at near-relativistic speeds. Knowing what kind of light signals are generated in such events will help modern observations to identify them and other processes in the heart of most galaxies.
The new simulation describes the behavior of supermassive black holes 40 orbits before merging. The model shows that radiation predominantly occurs in ultraviolet and high-energy X-rays, similar to what is observed in any galaxy with a supermassive central black hole.
Three regions of radiating gas glow as black holes merge and are enveloped in streams of hot gas: a large ring surrounding the entire system and two smaller discs around each. All of these objects emit predominantly ultraviolet radiation. As gas pours into the smaller ring, the disk's ultraviolet light interacts with the black hole's corona, a region of high-energy subatomic particles above and below the disk, which produces X-rays. At a lower accretion rate, X-rays dominate over ultraviolet light.
Based on simulations, the researchers expect the X-rays emitted before the merger to be brighter and more variable than those observed from single supermassive black holes.
The simulation was carried out on a supercomputer at the University of Illinois at Urbana-Champaign (USA) and took 46 days on 9600 computational cores. The team plans to refine the code to assess the effects of changes in the system's input parameters (such as temperature, distance, total mass, and accretion rate) on the emitted light, and to understand what happens to gas traveling between two black holes over longer periods of time. If their efforts lead to the expected results, astrophysicists can detect supermassive black hole mergers before the space gravitational wave observatory sees them.
MOSCOW, September 26 - RIA Novosti. The LIGO and VIRGO gravitational observatories for the first time simultaneously detected a burst of gravitational waves generated by the merger of two black holes and localized their source - one of the galaxies in the constellation of the Hours, said participants in the VIRGO and LIGO collaborations, speaking at a press briefing at the meeting of the G7 ministers in Italian Turin.
"The combination of LIGO and VIRGO not only increased the accuracy of localization of sources of gravitational waves 20 times, but also allowed us to start searching for traces of objects generating gravitational waves in other types of radiation. Today we have truly entered the era of full-fledged gravitational astronomy", - said David Shoemaker, head of the LIGO collaboration.
Interstellar physicist: film helped us see real black holesFamous american physicist Kip Thorne, one of the screenwriters of the Interstellar film, told RIA Novosti why the LIGO gravitational detector deceived the expectations of most scientists, whether he believes in the colonization of Mars and "wormholes", and shared his thoughts on how the film was shot helped science.Looking for folds of space-time
The LIGO gravitational wave detector was built in 2002 according to designs and plans that were developed by Kip Thorn, Rainer Weiss and Ronald Drever in the late 1980s. At the first stage of its work, which lasted 8 years, LIGO was unable to detect the "Einstein" oscillations of space-time, after which the detector was turned off and the next 4 years, scientists spent on updating and increasing the sensitivity.
These efforts paid off - in September 2015, almost immediately after the inclusion of the updated LIGO, scientists discovered a burst of gravitational waves generated by merging black holes with a total mass of 53 Suns. Subsequently, LIGO recorded three more bursts of gravitational waves, only one of which was officially recognized by the scientific community.
Scientists do not know exactly where the sources of these gravitational waves were located - due to the fact that LIGO has only two detectors, they only managed to isolate a fairly narrow strip in the night sky where these black holes could be. Inside it, despite its modest size, there are millions of galaxies, which makes the search for the "end product" of these mergers virtually useless.
In June of this year, the European "cousin" of LIGO, the VIRGO gravitational observatory, built in the vicinity of Pisa, Italy in 2003, resumed its work. The operation of VIRGO was suspended in 2011, after which the observatory's engineering team carried out a deep modernization, bringing it closer in sensitivity to the current level of LIGO.
All inspections of the VIRGO detectors were completed by 1 August this year, and now the observatory has begun joint observations with two LIGO detectors. Its sensitivity is slightly lower than that of the American gravitational telescope, but the data it receives allows it to solve two major scientific problems - to improve the quality and reliability of the signal received by LIGO, and to determine the "three-dimensional" position of the source of gravitational waves.
Einstein Triangulation
Scientists achieved the first results unexpectedly quickly - already on August 14, they managed to detect the burst GW170814, which originated in a distant galaxy at a distance of 1.8 billion light years from Earth. As in the previous three cases, these waves were generated by unusually large black holes, whose mass was 30.5 and 25 times greater than the sun. During their merger, approximately three solar masses "evaporated" and were spent on the emission of gravitational waves.
The use of three detectors at once allowed scientists to significantly increase the accuracy of localizing the source of gravitational waves - the galaxy in which the black holes that generated them are located is located in a small area of \u200b\u200bthe sky in the constellation of Hours in the night sky of the southern hemisphere of the Earth. In addition, scientists plan to use this data to search for possible traces of this outbreak in the radio and X-ray ranges.
Physicist: the discovery of gravitational waves is the key to understanding the life of the universeThe International Gravitational Observatory LIGO announced the phenomenal detection of gravitational waves, whose discovery, according to the Russian physicist Mikhail Gorodetsky, opens the way for us to create theories quantum gravity and the theory of "grand unification", which explains all processes in the universe.There was no sensation in this case - preliminary analysis of the data collected by LIGO and VIRGO during this outbreak shows that gravitational waves travel through space and behave exactly as predicted by Einstein's theory. In the future, when the sensitivity of LIGO and VIRGO is increased, scientists hope to find a definitive answer to this question.
Shoemaker noted that the LIGO detectors were turned off on August 25 in order to approximately double their accuracy. This "upgrade", he said, will expand the "horizon of vision" of the observatory by about nine times, and will allow traces of merging black holes to be found almost every week.