New observations suggest that a rare gamma-ray burst (gamma burst) affected by gravitational lensing may indicate that its light passes near a medium-sized black hole.
There are two common sizes of black holes today: so-called stellar black holes, which are typically three to ten times the mass of the Sun, and supermassive black holes, which exist at the centers of most galaxies, including our own Milky Way, and weigh millions to billions of times the mass of the Sun.
But medium-sized black holes in between these two types of black holes are very rare. This raises an important question in astronomy: How do supermassive black holes form?
So far, only a small number of intermediate black holes, i.e., those with masses between 100 and 100,000 solar masses, have been detected, and none of them lies exactly in the middle of that range.
The newly discovered gravitational lensing black hole, which happens to be about 55,000 solar masses, may be the missing link between stellar and supermassive black holes.
Professor Eric Thrane of Monash University (Australia) said in a statement that the newly discovered black hole “may be an ancient relic, a primordial black hole that formed before the first stars and galaxies.”
A black hole is a celestial body that compresses a massive object into a tiny space. Their gravitational pull is so strong that they cannot even escape them without light. And when light passes near a black hole, it is distorted by the black hole’s powerful gravitational force, as if it were passing through a magnifying glass. This phenomenon is known as the gravitational lensing phenomenon.
In this case, light from a distant object that passes through this gravitational lens will have to pass through a curved path, so that it will reach Earth later than light that is not affected by the gravitational lens.
The team used the latest technology to analyze hundreds of gamma bursts to try to find a sample of those affected by gravitational lensing. Eventually, the team noticed this discovery of a gamma burst, which is about 8 billion light years from Earth.
Although the team was able to accurately measure the mass of the medium-sized black hole using the phenomenon of gravitational lensing, they could only speculate on how the black hole formed: one possibility is that it was formed by the merger of two smaller black holes; alternatively, it could have been a black hole from the stellar level, slowly accumulating mass by continuously swallowing the surrounding matter.
“But it’s a slow process,” said Professor Rachel Webster of the University of Melbourne, Australia, in the same statement. “In the age of the universe, it’s hard to grow supermassive black holes from solar-mass seeds.”
The team believes there are about 40,000 intermediate black holes in our own galaxy alone.
The new study is published in the March 29, 2021 issue of Nature Astronomy.
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