Washington, United States

Astronomers have discovered a black hole that contains 200,000 times the mass of the Sun buried in gas and dust in the galaxy Mrk 462.

Advertisment

Black holes are extremely dense, with gravitational pulls so ferocious, not even light escapes. Cygnus X-1 is the Milky Way’s largest-known stellar-mass black hole and among the strongest X-ray sources seen from Earth.

Also read | Scientists discover new type of nebulae around binary stars

There are three categories of black holes. The smallest, like 'the Unicorn,' are so-called stellar-mass black holes formed by the gravitational collapse of a single star. There are gargantuan 'supermassive' black holes like the one at our galaxy's center, 26,000 light-years from Earth, which is four million times the sun's mass. A few intermediate-mass black holes also have been found with masses somewhere in between.

Advertisment

Mrk 462 contains only several hundred million stars, making it a dwarf galaxy. By contrast, our Milky Way is home to a few hundred billion stars. This is one of the first times that a heavily buried, or "obscured," supermassive black hole has been found in a dwarf galaxy.

Also read | Chemical leftovers from Earth's creation still lingering deep within our planet: Study

The discovery of this supermassive black hole in a relatively small galaxy could help astronomers unravel the mystery surrounding how the very biggest black holes grow. They identified it using by NASA's Chandra X-ray Observatory. 

Advertisment

"This black hole in Mrk 462 is among the smallest of the supermassive, or monster, black holes," said Jack Parker of Dartmouth College in New Hampshire, who led the study with colleague Ryan Hickox, also from Dartmouth. "Black holes like this are notoriously hard to find."

Also read | Astronomers publish most detailed map to date of black holes

The unusually large intensity of high-energy X-rays compared to low energy X-rays, along with comparisons to data at other wavelengths, indicates that the Mrk 462 black hole is heavily obscured by gas.

"Because buried black holes are even harder to detect than exposed ones, finding this example might mean there are a lot more dwarf galaxies out there with similar black holes," said Hickox. 

"This is important because it could help address a major question in astrophysics: How did black holes get so big so early in the universe?"

A large fraction of dwarf galaxies with supermassive black holes favours the idea that small black hole seeds from the earliest generation of stars grew astonishingly quickly to form the billion solar mass objects in the early universe.

A smaller fraction would tip the scales to favor the idea that black holes began life weighing tens of thousands of Suns.

These expectations apply because the conditions necessary for the direct collapse from a giant cloud to a medium-sized black hole should be rare, so it is not expected that a large fraction of dwarf galaxies would contain supermassive black holes.

Stellar-mass black holes, on the other hand, are expected in every galaxy.

"We can't make strong conclusions from one example, but this result should encourage much more extensive searches for buried black holes in dwarf galaxies," said Parker. "We're excited about what we might learn."

(With inputs from agencies)