Apparently, the supermassive black hole (SMBH) hanging around in the middle of the Milky Way has a lot of company. The scientific community has long suspected the existence of several smaller black holes surrounding this leviathan known as Sagittarius A* (Sgr A*). For over two decades, scientists searched unsuccessfully for evidence to support the theory that thousands of black holes surround SMBHs at the centre of large galaxies. Making their quest that much more difficult was the fact that black holes have been difficult to detect.
This leaves the Milky Way as the only ideal galaxy to explore how SMBHs interact with smaller ones. Observing this interaction is simply not possible in other galaxies.
In search of black holes
According to a new study published in the British journal ‘Nature’
, Sgr A* is surrounded by about 10 000 other black holes. Sgr A* is the easiest to study because it’s the closest SMBH to Earth, some 26 000 light years away. It’s around 4 million times the mass of the sun.
Sgr A* is surrounded by a halo of gas and dust that offer just the right conditions to give birth to massive stars. Such stars live, die and could turn into black holes there. Scientists believe that these black holes and others from outside the halo are drawn to Sgr A* and held captive around it.
Dr Chuck Hailey, co-director of the Columbia Astrophysics Lab in New York City and lead author on the study, told the UK’s ‘Independent’
: “This finding confirms a major theory and the implications are many. It is going to significantly advance gravitational wave research because knowing the number of black holes in the centre of a typical galaxy can help in better predicting how many gravitational wave events may be associated with them.” He added: “All the information astrophysicists need is at the centre of the galaxy.”
Galaxies are busy places
Using archival data from NASA’s premier X-ray telescope, Dr Hailey and a team of astrophysicists at Columbia University searched for X-ray signatures of black hole-low mass binaries in their inactive state. They found 12 within 3 light years of Sgr A*. The team then analysed the properties and spatial distribution of the identified binary systems. From observations, the scientists concluded that there must be anywhere from 300 to 500 black hole-low mass binaries and about 10 000 isolated black holes in the area surrounding Sgr A*.
Quoted by the ‘BBC’
, Dr Hailey said: “Isolated, unmated black holes are just black – they don’t do anything. But when black holes mate with a low mass star, the marriage emits X-ray bursts that are weaker, but consistent and detectable.”
This seminal research should pave the way for a better understanding of the Milky Way. The hunt is now on for these elusive black holes, one of the most fascinating objects in our universe.