Object LGGS J004527.30 + 413254.3 (J0045 + 41 for brevity), which astronomers previously considered part of the Andromeda nebula, turned out to be the closest in the history of observations by a pair of supermassive black holes.
The discovery was made by a research group from the University of Washington: Trevor Dorn-Wallenstein, Emily Levesque and John Ruan. The scientific article with the results of the research was accepted for publication in the Astrophysical Journal, but for the time being it is available on the website of the preprints arXiv.org.
A black hole is called supermassive if it exceeds by mass the Sun hundreds of thousands of times or more. Such objects are observed due to the radiation of the substance incident on them. They are found in the center of many galaxies, including our own.
It is quite rare to find a pair of supermassive black holes circling around the common center of mass. The system, discovered by American astronomers, turned out to be a record close, that is, the distance between the two components of the pair is unusually small.
The Andromeda nebula, also M31, is a large and beautiful spiral galaxy, located about 2.5 million light-years from Earth. Object J0045 + 41 was previously considered a double star with a period of revolution of 80 days, which was part of this galaxy. A double star is a system of two luminaries revolving around a common center of mass.
But a group from the University of Washington, using the data of the orbital X-ray observatory Chandra, discovered that the celestial body emits a powerful stream of X-rays. Stars, even double ones, do not behave this way. There was an assumption that one of the components of the system is a neutron star or a black hole on which the companion matter falls. Experts call this process accretion. Accelerating and warming up during the tug-of-war, such a substance will serve as a source of “X-rays.”
However, observations of the object in the Gemini-North optical telescope in Hawaii have refuted this version. The resulting spectrum made it possible to determine the redshift of the object, and hence the distance to it. It turned out that it is 2.6 billion light years, that is, more than a thousand times greater than the distance to the Andromeda nebula.
No system of stars and black holes of stellar mass can be discerned from such a distance. That’s how in astronomy you can change the look at the nature of the object, simply by measuring the distance to it.
The spectrum of the object also indicated that it is still double. There are two components in it that move relative to each other with a considerable speed of 4800 kilometers per second. Astronomers understood this by using the Doppler effect.
Scientists used the optical telescope project Palomar Transient Factory in California, in order to explore in detail how its shine varies with time. They found that the brightness varies according to a complex law, including several oscillations with different periods, including 80 and 320 days. The presence of two periods related to each other as 1: 4 is important: this is the prediction theoretically for a pair of supermassive black holes.
“For the first time, there was such compelling evidence that we have a pair of rotating giant black holes in front of us,” Emily Levesque quotes a press release from the study.
Such pairs are likely to be formed in the collision of galaxies, each of which has a black hole in the center. Although it can not be ruled out that such a duet can arise without space “road accidents”. The processes of formation of supermassive black holes to astronomers are not yet fully known.
Object J0045 + 41 turned out to be a record not only for reliability, with which it can be identified as such a pair. The tandem turned out to be also very close: the distance between the components is less than a hundredth part of the light year.
Such close relations are fraught with a catastrophe. Black holes lose energy on the radiation of gravitational waves, get even closer together, lose more energy and so on. From this vicious circle there is no way out except for a collision.
Astronomers are at a loss to say when it will happen. Although they estimated the total mass of the two components (200 million solar), it is not known what proportion it has to each of the partners. Therefore, it is difficult to say how much they remained until they merged into a single whole. You can only specify the range of possible values: from 350 years to 360 thousand years.
This collision, of course, also generates gravitational waves. Unfortunately, current detectors are not able to record such events: the wave period (the time interval between the two oscillations) will be too large.