(Kailash C. Sahu et al. / arxiv.org, 2022)
Astronomers have reported the first detection of a "wandering" stellar-mass black hole using gravitational microlensing.
To do this, they collected data from the Hubble telescope for six years.
Their analysis made it possible to measure its position, mass, and also the speed of the movement.
Black holes of stellar mass (that is, from five to several tens of solar masses) can form as a result of the evolution of very massive stars.
At the end of their lives, such stars explode as supernovae and can give rise to black holes.
As a rule, it is possible to detect such objects if there is another star in the neighborhood of such a black hole.
In particular, stellar-mass black holes that are part of a binary system are detected by their influence on the motions of their companions, by the characteristic accretion disk consisting of star gas, and also by gravitational waves emanating from such systems.
However, these methods are not suitable for black holes that fly freely in interstellar space.
The only method applicable in this case is the search for microlensing effects, which is rather weak in the case of such black holes.
Using the Space Telescope, a team of astronomers, with the participation of Kailash Sahu of the Institute for Space Studies, has been able to prove that an isolated stellar-mass black hole is indeed responsible for the lensing previously found in the Hubble data.
They not only calculated its mass, which turned out to be approximately equal to seven solar masses, but also determined its speed of movement.
In 2011, the OGLE (Optical Gravitational Lensing Experiment) and MOA (Microlensing Observations in Astrophysics) projects detected the MOA-11-191/OGLE-11-0462 event, which involved microlensing of one of the stars close to the center of the galaxy.
In particular, astronomers saw that it began to shine brighter for no apparent reason. This behavior could be caused by a "wandering" black hole.
To confirm this hypothesis, astronomers continued to monitor this area for another six years.
By observing the deflection of light with an accuracy of about 0.2 milliseconds of arc, the authors concluded that the object that creates the gravitational lens is located at a distance of just over five thousand light years and has a mass equal to 7.1 ± 1.3 solar masses.
The absence of additional radiation testified in favor of a black hole. Astronomers also managed to calculate its speed: it turned out to be 45 kilometers per second.
The authors suggest that such a speed could be caused by a push from the explosion of a single supernova that gave rise to a black hole.
Source:
Arxiv: https://arxiv.org/abs/2201.13296
Universe Today: https://www.universetoday.com/154420/the-first-rogue-black-hole-has-been-discovered-and-its-only-5000-light-years-away/