Intermediate-mass black hole

An intermediate-mass black hole (IMBH) is a special kind of black hole. Its mass ranges from one hundred to one hundred thousand times the mass of our Sun. This makes it much bigger than the black holes formed when big stars end their lives, called stellar black holes, but much smaller than the giant black holes found at the centers of galaxies, known as supermassive black holes.

Scientists have found several possible IMBHs, especially in our own galaxy, the Milky Way. They discover these hidden giants by watching how nearby gas clouds move and by studying the light from material being pulled into the black hole. These clues help astronomers learn about these mysterious objects. Studying IMBHs helps us understand how bigger black holes might form and how they influence the space around them.

Observational evidence

Scientists think there might be intermediate-mass black holes. These are bigger than black holes made from single stars but smaller than the huge black holes in the centers of galaxies.

One clue came from a gravitational wave signal found on May 21, 2019. This signal showed two black holes merging. One was 85 times the mass of our Sun, and the other was 65 times the mass of our Sun.

Other clues come from very bright areas in galaxies that shine in X-ray light. These areas are called ultraluminous X-ray sources. They might be caused by intermediate-mass black holes. Scientists also watch how stars move in clusters to find more evidence of these mysterious black holes.

Potential discoveries

In November 2004, astronomers found GCIRS 13E in the Milky Way. They thought it might be the first intermediate-mass black hole. It was thought to be 1,300 times the mass of the Sun and was near Sagittarius A*.

Since then, more possible intermediate-mass black holes have been found. In 2009, HLX-1 was found in the galaxy ESO 243–49. In 2012, another possible black hole was found by a team using the CSIRO radio telescope in Australia. In 2015, a gas cloud moved in a way that suggested a black hole about 100,000 times the mass of the Sun might be there. In 2018, another possible black hole was found near the center of our galaxy, called HCN-0.009-0.044, with a mass of 32,000 solar masses.

In 2019, scientists observed a gravitational wave event (GW190521) from two smaller black holes merging into one that was 142 times the mass of the Sun. In 2020, a possible intermediate-mass black hole was found in the Aquarius constellation, and in 2021, a very massive black hole candidate was found in the Andromeda Galaxy. Scientists are still looking for more clues about these interesting objects.

Origin

Intermediate-mass black holes are larger than the black holes that form when a single star collapses. They are too big to come from one star and do not form in the centers of galaxies where supermassive black holes are found. Scientists think intermediate-mass black holes might form in three ways: by smaller black holes merging, by many large stars crashing together and collapsing, or by being special black holes created very early in the universe during the Big Bang. Some theories also suggest they could form from extremely massive stars, but this is less likely.