The observations could shed light on the mystery of the structure of neutron stars and the formation of heavy elements in the Universe
An artistic representation of gravitational waves generated by the merger of two neutron zvezdopada: R. Hurt/Caltech-JPL
Scientists for the first time in the history of recorded gravitational waves from the merger of two neutron stars — super dense objects with mass of our Sun and the size of Moscow, the website of N+1.
Then caused a gamma-ray burst and flash bulanovoi watched about 70 ground-based and space-based observatories — they were able to see theorists predicted the synthesis of heavy elements, including gold and platinum, and to confirm the correctness of the hypotheses about the nature of the mysterious short gamma-ray bursts, according to the press service of the collaboration LIGO/Virgo, the European southern Observatory and the Observatory, Los Cumbres. The results of observations may shed light on the mystery of the structure of neutron stars and the formation of heavy elements in the Universe.
Gravitational waves — waves of fluctuations in the geometry of space-time, the existence of which was predicted by the General theory of relativity. For the first time about their reliable detection by LIGO collaboration announced in February 2016 — 100 years after Einstein’s predictions.
Reportedly, on the morning of August 17, 2017 (8:41 on the East coast of the United States, when in Moscow 15:41) automatic system at one of two detectors gravitational-wave Observatory LIGO registered the arrival of gravitational waves from space. The signal received the designation GW170817, it was already the fifth case of fixation of gravitational waves from 2015, from when they were first registered. Just three days before the LIGO Observatory for the first time “heard” gravitational wave together with the European project Virgo.
This time, two seconds after gravitational events space telescope Fermi has recorded a flash of gamma radiation in the southern sky. Almost at the same time the flash saw the European-Russian space Observatory INTEGRAL.
Automatic data analysis systems Observatory LIGO came to the conclusion that the coincidence of these two events is extremely unlikely. In seeking additional information, it was discovered that the gravitational wave saw the second LIGO detector, as well as the European gravitational Observatory, Virgo. Astronomers around the world were raised by alarm — the hunt for the source of the gravitational waves and gamma-ray burst began many observatories including the European southern Observatory and space telescope Hubble.
The task was not easy — the combined data LIGO/Virgo, Fermi, and INTEGRAL allowed us to outline the region with an area of 35 square degrees is the approximate size of several hundred lunar disk. Only 11 hours light meter Swope telescope with a mirror located in Chile, made the first the possible cause — he looked like a very bright star next to the elliptical galaxy NGC 4993 in the constellation Hydra. Over the next five days, the source brightness fell 20 times, and the color gradually shifted from blue to red. All this time the object was observed by many telescopes in the range of x-ray to the infrared, while in September, the galaxy was not too close to the Sun, and was not available for observation.
Scientists came to the conclusion that the source of the outbreak was located in the galaxy NGC 4993 at a distance of about 130 million light years from Earth. It’s incredibly close, so far gravitational waves come to us from distances of billions of light years. Thanks to this proximity, we were able to hear them. The source wave was a merger of two objects with masses in the range from 1.1 to 1.6 solar masses — it could only be a neutron star.
Localization of the source of gravitational waves in the galaxy NGC 4993
The surge “was” a very long time — about 100 seconds, mergers of black holes gave bursts lasting fractions of a second. A pair of neutron stars rotate around a common center of mass, gradually losing energy in the form of gravitational waves and getting closer. When the distance between them was reduced to 300 km, the gravitational waves become powerful enough to get into the zone of sensitivity of the gravitational detectors LIGO/Virgo. Neutron stars managed to make 1.5 thousand revolutions around each other. At the time of the merger of two neutron stars into a single compact object (neutron star or black hole) is powerful flash of gamma radiation.
Such gamma-ray burst astronomers call short gamma ray bursts, gamma-ray telescopes fix them about once a week. The short GRB from a neutron stars merger, which was reported to have lasted 1.7 seconds.
If nature of long gamma ray bursts is more understandable (their sources — supernova), consensus about the sources of the short bursts were not. There was a hypothesis that they are generated by merging neutron stars.
Now for the first time scientists have been able to confirm this hypothesis, because the gravitational waves, we know the mass of fused components, which proves that it is a neutron star.
“Decades, we suspected that a short gamma-ray bursts give rise to the merger of neutron stars. Now, using data from the LIGO and Virgo about this event we have the answer. Gravitational waves tell us that merged objects have mass, appropriate neutron stars, and gamma-ray flash says that these objects could be black holes, since the collision of black holes should not result in radiation,” says Julie McEnery, project officer Fermi space flight Center of NASA Goddard.
Source of gold and platinum
In addition, astronomers for the first time received a definite confirmation of the existence milonovich (or “macanovic”) flashes, which is approximately 1 thousand times more powerful outbreaks of a new routine. Theorists predicted that kilobye can occur when merging neutron stars or a neutron star and a black hole.
This starts the process of synthesis of heavy elements, based on the capture of neutrons by nuclei (r-process), which in the Universe there were many heavy elements such as gold, platinum or uranium.
According to scientists, the explosion of Bulanovoj can be a huge amount of gold to ten of the masses of the moon. So far only once been observed an event that could be the explosion of Bulanovoj.
Now, however, astronomers were able for the first time to observe not only the birth of Bulanovoj, but also the products of its “work”. Spectra obtained with telescopes Hubble and the VLT (Very Large Telescope) showed the presence of cesium, tellurium, gold, platinum and other heavy elements formed by neutron star mergers.
11 hours after the collision, the temperature of bulanovoi was 8 thousand degrees and the speed of its expansion has reached about 100 thousand kilometers per second, said N+1 with reference to data of the State astronomical Institute named after Sternberg (SAI).
In ESO reported that the observation almost perfectly coincided with the forecast of the behavior of two neutron stars merging.
“While the data that we obtained, perfectly consistent with the theory. This is a triumph for theorists, the confirmation of the absolute reality of events registered by the observatories LIGO and VIrgo, and the remarkable achievement of ESO, which managed to obtain such observations Bulanovoj,” says Stefano Covino, the first author of one of the papers in Nature Astronomy.
So the collision of neutron stars, astronomers saw
Scientists still no answer to the question of what remains after the merger of neutron stars — it may be like a black hole, and the new neutron star is, moreover, not quite clear why the gamma-ray burst was relatively weak.