A ‘monster mini black hole’ has been discovered in a small galaxy

With the Chandra telescope, astronomers have discovered a “monster mini black hole” in a dwarf galaxy. This copy can help understand how certain black holes were able to grow when the universe was still young.

It would be one of the smallest identified supermassive black holes. A “monster mini black hole” has just been discovered, buried in gas and dust from another galaxy, NASA reported on January 10, 2022.

This “mini” black hole, which is still about 200,000 times the mass of the Sun, seems to be growing. It is housed in a galaxy called Mrk 462, which contains only a few hundred million stars – making it a dwarf galaxy. By comparison, the Milky Way contains hundreds of billions of stars.

A freezer is stained thanks to X-rays

To find this black hole, the researchers used Chandra, a space-based X-ray observatory. The telescope pointed at 8 different dwarf galaxies. Hints of growing black holes in these galaxies had been seen earlier, as part of the Sloan Digitak Sky Survey, conducted by the Apache Point Observatory in New Mexico. Among the 8 galaxies, it is only the galaxy Mark 462 showed signs of the presence of a growing black hole in the X-ray domain.

A 'monster mini black hole' has been discovered in a small galaxy
X-rays detected at the level of the galaxy Mrk 462. // Source: X-ray: NASA / CXC / Dartmouth Coll./J. Parker & R. Hickox; Optical / IR: Pan-STARRS

Usually, astronomers prefer to use the motion of stars in the heart of galaxies to locate black holes. But this method works mainly for fairly large galaxies. Dwarf galaxies are too dark and small. Another way to do this is to look for the gas that falls into the black hole: it heats up to millions of degrees and shines in the X-ray domain. That is what has been done here.

In the case of the galaxy Mrk 462, scientists were able to observe that the black hole must be particularly hidden by the gas that surrounds it. Such buried black holes are difficult to detect, but the example of Mrk 462 opens up an interesting perspective: perhaps dwarf galaxies housing similar black holes are widespread. To could be very helpful in better understanding how the largest black holes in our universe grow.


Sad black hole in the Milky Way.  // Source: NASA, Numerama Editing

A mystery about the giant black holes in the early universe

Previous work has shown that when the universe was less than a billion years old – it is currently 14 billion years old – some black holes already reached a mass equivalent to a billion suns. How these colossi were able to flourish so early in the universe is still poorly understood. There are several hypotheses:

  • Large black holes would be born from the collapse of massive stars. They would weigh about 100 times the mass of the Sun – but it is not known how they could have grown so fast to reach the masses observed in the still young universe.
  • Black holes already containing tens of thousands of solar masses would have been created in the young universe from the collapse of large clouds of gas and dust.

Discoveries about dwarf galaxies containing supermassive black holes can help determine between the hypotheses: if they are widespread, the first scenario seems more likely; if they are quite rare, it will rather favor the second option. In other words: the percentage of dwarf galaxies with supermassive black holes would help understand the growth of some of the first black holes in the universe.

The example of Mark 462 and its growing black hole have not yet solved the mystery, but astronomers believe it should encourage further research into large black holes buried in dwarf galaxies.

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