Thousands of black holes could be lurking at the centre of the Milky Way

5 Apr 2018

Spiral galaxy NGC 1097, a structure similar to our own Milky Way. Image: NASA

A new study from Columbia University confirms a major theory about our galaxy.

For many decades, there has been a theory that the centre of every galaxy contains a supermassive black hole that contains countless solar masses worth of material in one specific location.

As well as this, it has long been posited that there should be fast-moving stars and thousands of smaller black holes surrounding it.

Future Human

This previously unproven theory has now become that bit more plausible, thanks to a study conducted by researchers at Columbia University, published in scientific journal Nature.

The researchers used archival data from NASA’s Chandra X-ray Observatory to discover a dozen inactive and low-mass binary systems, whereby a star is orbiting a black hole.

Supermassive Sagittarius A*

The centre of the Milky Way contains a supermassive black hole called Sagittarius A* (Sgr A*), which is surrounded by a scattering of dust and gas, where many stars are born. The study also found that black holes from outside the surroundings of Sgr A* are pulled into the vicinity of it as they lose energy.

Some of these black holes pair up with passing stars, creating the binary systems discovered by the Columbia research team. Previous attempts to locate this population of smaller black holes involved searching for bursts of x-rays, which black hole binaries can sometimes emit.

These bursts are only bright enough to be seen about once every 100 to 1,000 years, according to astrophysics professor and lead study author Dr Chuck Hailey. This time, scientists looked for x-rays that were fainter but emitted in a more steady way when the binaries are inactive.

He explained to National Geographic that their discovery has led them to conclude that the visible black holes found are only a sample of those that exist. “Imagine you were standing in a football field, and you had a whole pile of 100-watt lightbulbs and 10-watt lightbulbs.” He continued, explaining that if you spread those bulbs out a mile away, “you could still see the 100-watt ones, but you might not see the 10-watt ones. By knowing what the ratio was in the football field, you could figure out how many dim ones you missed at a mile away.”

The researchers located evidence for 300 to 500 black hole binary systems, from which they were then able to estimate how many isolated black holes exist in the galactic centre – approximately 10,000.

Major boost for gravitational-wave research

This finding has some massive implications for the future study of gravitational waves, the ripples in spacetime triggered by massive cosmic events. By finding out where the black holes are and how many exist, scientists examining cosmic phenomena can try and predict when waves can be attributed to black holes.

“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,” Hailey explained.

He summed up the findings and the discoveries that lie ahead: “All the information astrophysicists need is at the centre of the galaxy.”

Ellen Tannam was a journalist with Silicon Republic, covering all manner of business and tech subjects