A 3 billion-years-old gravitationally lensed gamma-ray burst helped scientists discover an intermediate-mass black hole.
Astronomers have discovered a new candidate for a black hole of intermediate masses. It is assumed that it has a mass of 55 thousand times the mass of the Sun and acted as a gravitational lens for a short gamma-ray burst that exploded more than 3 billion years ago, thanks to which it was discovered.
Today, astronomers are aware of the existence of both black holes of stellar masses, which are formed at the end of the life of massive stars, and supermassive black holes (10 6 -10 10 solar masses), which are usually found in the centers of many galaxies.
However, theories predict the existence of intermediate-mass black holes, which are located between “stellar” and supermassive black holes. It is believed that such objects can help to understand how in the early universe black holes could quickly gain mass.
Despite the fact that there may be several hundred such objects in the Milky Way, their search is extremely difficult. So far, scientists have only candidates for intermediate-mass black holes, which have been found in dwarf galaxies, globular clusters, hyper-powerful X-ray sources, and even recorded a gravitational burst from a possible event of the birth of such a black hole.
Discovering a black hole through the light of a 3 billion-year-old gamma-ray burst
A group of astronomers led by James Paynter of the University of Melbourne reported the results of an analysis of a sample of 2.7 thousand GRBs recorded by the BATSE instrument, which operated at the Compton Space Observatory.
The goal of the scientists was to search for unusual bursts that would look like an initial pulse of gamma radiation, followed by a duplicate echo. Such a burst structure could arise in a situation where there would be a black hole between the terrestrial observer and the gamma-ray source, which would act as a gravitational lens.
In this case, the duration of the time delay between the main burst of radiation and the echo mainly depends on the mass of the gravitational lens, but also on the orientation of the gamma-ray source.
The result of the analysis was a short gamma-ray burst GRB 950830, an echo in which, according to scientists, indicates that a black hole of intermediate-mass could have played the role of a gravitational lens.
The researchers do not exclude that GRB 950830 was gravitationally lensed by a globular cluster, but in their opinion, this is unlikely due to the low spatial density of such objects.
According to the calculations of researchers in the vicinity of the Milky Way, there should be about 46 thousand black holes of intermediate masses. Further search for new candidates in gamma-ray burst catalogs can confirm this result and allow one to determine the spatial density of black holes of intermediate masses in the Universe.
But how incredible is it that we can observe a certain “invisible” celestial object through the influence of a phenomenon that occurred billions of years ago?
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Sources:
• Gohd, C. (2021, March 29). Explosion from the early universe illuminates secret black hole.
• Hood, M. (n.d.). A gamma-ray burst just revealed a ‘goldilocks’ black hole in the early universe.
• Paynter, J., Webster, R., & Thrane, E. (2021, March 29). Evidence for an intermediate-mass black hole from a gravitationally lensed gamma-ray burst.
