Astronomers have found a pair of superheavy black holes, almost touching each other

© Photo : ESO/ M. Complet the artist imagined the quasarAstronomers have found a pair of superheavy black holes, almost touching each other© Photo : ESO/ M. Kornmesser

Astronomers have discovered in the galaxy NGC 7674 pair of supermassive black holes, distant from each other by only one light year, and are ready to merge into a larger object, according to a paper published in the journal Nature Astronomy.

«This pair of black holes is at a distance of about 400 million light years from Earth, is about two times closer than black holes in the galaxy 4C +37.11 or galaxy OJ 287. This, however, does not make it more convenient for observing gravitational waves, since, because of combinations of factors, they will not see any «Polarnye» detectors like LIGO, or even eLISA,» write Harb Preeti (Preeti Kharb) from the University of Pune (India) and her colleagues.

The launch of the upgraded detector LIGO and the detection of more bursts of gravitational waves generated by merging black holes, once again showed that such events occur in the Universe often enough. However, to date, scientists have known of only two galaxies, where black holes are very close to each other — OJ 287 and 4C +37.11.

A small number of such objects and a large distance to them prevented scientists to study the properties of such black holes, including what role mergers may play in the formation of galaxies in the «strangulation» of star formation in them.

Harb and her colleagues added their number another interesting object, examining the «tail» of a black hole in the center of the spiral galaxy NGC 7674, distant from us by about 400 million light years and is located in the constellation Pegasus. Its unusually great length – about two thousand light-years and the structure has long made scientists to believe that at the center of this spiral galaxy can live not just one, but two black holes.

Watching her with the help of the radio eVLA, the «Union» of several radio telescopes are combined in one virtual radiotrance, scientists have discovered that in its center has not one, but two sources of radio emission. Their high brightness and the speed of movement indicate only a single possible version of their nature – they are both supermassive black holes.

The total mass of these black holes, according to scientists, is about 36 million solar masses, and they make one revolution around their common centre of mass approximately 100 thousand years. Such a short duration of the «year» in these black holes surprised Harb and her team, as it means that these objects are very close to each other – they are only 420 light-days, or 1.1 light years.

Such a close neighborhood of black holes and the very fact of their rotation around each other talking about what they produce strong enough gravitational waves now. These waves, despite the rather small distance between NGC 7674 and the Milky Way, can not be seen with LIGO or the space of the gravitational detector eLISA, the construction of which was recently approved by ESA.

The reasons for this, as the scientists explain, different – LIGO simply not adapted to detect low frequency gravitational waves that produce supermassive black holes. In turn, the «triangle» probes eLISA designed for observations of mergers of black holes-heavyweights, will not see them for the reason that the mass of the objects in the center of NGC 7674 is too small for it to be able to notice them.

On the other hand, the opening of the first real traces of two black holes in the center of spiral galaxies suggests that their collision and merging with other large «family of stars» do not always lead to the birth of elliptical galaxies, star formation processes are rapidly extinguished due to heating of the gas by the emissions of these black holes. Apparently, there are different mechanisms of merging galaxies and black holes, which scientists have not yet discovered, make Harb and her colleagues.