It is not the smallest nor the largest, but precisely one that is in an elusive middle category. A team of astronomers from the University of Melbourne (Australia) has discovered an unusual black hole “Goldilocks” that has approximately 55,000 times the mass of the Sun, and that “is neither too big nor too small” but of a black hole of intermediate size; a missing link between the two populations of these invisible structures that are capable of tearing stars apart and engulfing space-time (the stellar class, about 3-10 times the mass of our Sun and the supermassive, which are millions or thousands of millions more massive).
Stellar-class black holes form when a dying star collapses. Regarding supermassive black holes … we are still missing pieces of the puzzle of these matter-eaters to certify their exact origin .
How did they find out?
Most of the black holes we’ve observed are stellar or supermassive, but intermediate-mass black holes have been more elusive.
The discovery of this evidence has been possible thanks to a cataclysmic explosion : a burst of gamma rays; a half-second flash of high-energy light. Gamma-ray bursts are incredible releases of energy, coming from extremely bright supernovae or from a fusion of stars whose light was aligned with the black hole. As black holes warp spacetime around them, this warp creates a gravitational lensing, so the light from the gamma-ray burst is magnified and distorted by the presence of this black hole.
The researchers adapted powerful software developed to detect black holes from gravitational waves to establish that the two flares were images of the same object. This allowed some estimates to be made about the elusive intermediate-mass black hole.
A primordial black hole
According to experts, it could be an ‘ancient relic’ that dates back to before the first stars and galaxies were formed in the universe, as suggested by the authors in the journal Nature Astronomy that collects the study. In fact, it is believed that they possibly embody the seeds of what would later become the supermassive black holes that live in the heart of galaxies, such as Sagittarius A *, of our Milky Way (or the recently photographed M87 of which we have been able to observe the magnetic field surrounding this gravitational monster, which is three million times larger than Earth).
The intermediate-mass black hole is 3 billion light-years away, and researchers estimate that there are some 46,000 intermediate-mass black holes in the vicinity of our cosmic neighborhood.
“Using this new black hole candidate, we can estimate the total number of these objects in the universe. We predicted that this could be possible 30 years ago, and it is exciting to have discovered a solid example ,” explains Rachel Webster of the University of Melbourne and co-author of the work.
Referencia: Evidence for an intermediate-mass black hole from a gravitationally lensed gamma-ray burst, Nature Astronomy (2021). DOI: 10.1038/s41550-021-01307-1
