Massive black hole found in unlikely place

Supermassive black holes are a common feature at the centre of galaxies, but have only ever been found in those specimens densely populated by stars - until now.

Close up of the centre of NGC 1600, showing a diffuse core as if many stars are missing
Credit: Gemini Observatory/AURA & HST/NASA/ESA

Close up of the centre of NGC 1600, showing a diffuse core as if many stars are missing. Image Credit: Gemini Observatory/AURA & HST/NASA/ESA

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Astronomers have discovered a massive black hole weighing the same as 17 billion Suns in a sparsely populated galaxy, revealing for the first time that black holes of this size may be more common than thought.

The black hole was found in the centre of elliptical galaxy NGC 1600 among a small grouping of about 20 galaxies.

Although it is one of the most massive black holes found to date, its host galaxy lacks the vast quantities of stars usually associated with black holes of this size.

Supermassive black holes can be found at the centre of most galaxies, including our own. In the early Universe, black holes a thousand times more massive than the one at the centre of our Galaxy power quasars through the accretion of cosmic gas, causing them to outshine their host galaxies.

But the descendants of these massive black holes are usually only found in huge galaxies at the centres of galaxy clusters.

One explanation for the sparse nature of the galaxy is that the black hole is the result of a merging of two galaxies with supermassive black holes at their centres.

This would cause the two central black holes to merge as well, creating one behemoth black hole that would eject close-by stars out of the galactic neighbourhood.

“Less massive elliptical galaxies typically get brighter and brighter the closer you get to the centre, but in NGC 1600 it’s like the equivalent of all the stars of the Milky Way disc have been removed,” says lead author Jens Thomas of the Max Planck Institute for Extraterrestrial Physics.

This discovery could well be the turning point in our perception of how common massive black holes are in the Universe.

“The black hole in NGC 1600 is the first example of a possible descendant of a luminous quasar in a relatively isolated galaxy,” says Chung-Pei Ma of the University California Berkley, who leads the MASSIVE survey that was used in the discovery.

“There are quite a few galaxies of comparable size that reside in average-sized galaxy groups.

At the moment we do not know if such very massive black holes are common in other nearby massive galaxies as well.

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Our ongoing observations will soon reveal if our discovery is a rare find or just the tip of an iceberg.”