Astronomers have just found evidence that shows a long-rumored black hole might be present in the Milky Way. The black hole appears to be mid-sized and not nearly as big as the giant ones present at the centers of galaxies.

If the find is confirmed it could show that our galaxy has grown by sucking out its smaller neighbors. Astronomers estimated the black hole has a mass of about 100,000 times that of our sun, and evidence points it’s a special kind of black hole that has long been theorized but never identified.

Image credit: Dana Berry, Skyworks Digital / NASA  / Nat Geo
Image credit: Dana Berry, Skyworks Digital / NASA
/ Nat Geo

Those types of black holes, known as intermediate-mass black holes (IMBHs) are thought to be the missing link in the evolution of cosmic objects and could help explain how supermassive black holes are formed. IMHBs have never been officially identified, though.

Candidate for intermediate-mass black hole has about mass of 100,000 suns

The astronomers published their findings in the journal Nature Astronomy. The research was led by Tomoharu Oka from Keio University in Yokohama, Japan, and colleagues. The researchers say they believe the discovery is a good candidate for an IMBH.

The discovery was made after they found a “peculiar” molecular cloud located near the center of the Milky Way, which according to the scientists displayed some highly unusual properties not seen in similar cosmic structures. The team noted those features could be explained by a “gravitational kick” caused by an “invisible compact object with a mass of about 105 solar masses,” Newsweek reports.

“It’s a very careful paper and they have gorgeous data,” Kevin Schawinski, an astronomer at the Swiss Federal Institute of Technology in Zurich, told Science Magazine. “It’s the most promising evidence so far.”

Black holes are difficult to spot because they don’t emit any light of their own. However, they can be identified by their influence on nearby objects. Scientists have found evidence for star-sized black holes – about ten times the sun’s mass—and supermassive ones, which contain millions or even billions of solar masses, in galactic cores.

Intermediate-sized black holes, on the other hand, have been eluded by astronomers and no evidence to prove their existence has been gathered. The best candidates have been so-called ultraluminous X-ray sources in other galaxies. Unfortunately, as there is little evidence scientists have suggested those aren’t IMBHs but smaller back holes ingesting at a fast rate.

The discovery was made after they found a “peculiar” molecular cloud located near the center of the Milky Way. Image credit:
The discovery was made after they found a “peculiar” molecular cloud located near the center of the Milky Way. Image credit:

Hypothetical intermediate-mass black hole is around 500 times less luminous as others

In 2016, Oka and colleagues from Keio University reported discovering a peculiar cloud of molecular gas, dubbed CO-0.40-0.22, near the center of the Milky Way. The National Astronomical Observatory of Japan analyzed the event with its Nobeyama radio telescope and found gas in the cloud was moving at several velocities, some of those so fast that the astronomers suspected something supermassive was hiding there. After performing simulations of the gas movements in the cloud, they were able to estimate something as large as the masses of 100,000 suns was inside it.

After making the discovery, Oka and colleagues have studied the gas cloud with other instruments, such as the Atacama Large Millimeter/submillimeter Array (ALMA), a collection of more than 60 dishes high in the Chilean Andes that observes shorter wavelengths than typical radio observatories

The researchers reported in their paper that while they studied CO-0.40-0.22 with ALMA, they detected a dense clump of gas near the center of the cloud, which also showed a broad range of velocities suggestive of a massive nearby object. The finding was also supported by further simulations of the gas movements.

Moreover, they found a source of radio waves next to the gas clump. The spectrum of the source seemed to be very similar to Sagittarius A* (Sgr A*), and they estimated the radio source was apparently the supermassive black hole at the center of our Milky Way, but around 500 times less luminous. Oka says the similarity with Sgr A* suggests there is an intermediate-mass black hole in the center of the Milky Way.

Astronomers will keep studying the IMBH candidate

Scientists have shared their excitement over the findings, as confirming the existence of an IMBH would open a new field of research to fully comprehend supermassive black holes, which can be billions of times the mass of our sun.

“It is widely accepted that black holes with masses greater than a million solar masses lurk at the centers of massive galaxies,” the authors of the new study wrote. “But the origins of such supermassive black holes remain unknown.”

The authors also noted confirming the existence of an IMBH could expand our understanding of the universe more generally.

“Theoretical studies have predicted that 100 million to one billion black holes should exist in the Milky Way, although only 60 or so have been identified through observations so far,” said the authors. “Further detection of such compact high-velocity features in various environments may increase the number of non-luminous black hole candidate and thereby increase targets to search for evidential proof of general relativity.”

They conclude their paper by saying that such a discovery would make a considerable contribution to the progress of modern physics. The team will continue studying the candidate to determine whether it is an IMBH or not.

Source: Science Magazine