Ultra-rare black hole found hiding in the center of the Milky Way

Astronomers have spotted a rare "'missing link"' black hole, and it's lurking right in the center of our galaxy.

The IRS 13 star cluster has long been a puzzle for astronomers. Located just a tenth of a light-year from the heart of our Milky Way galaxy where the Sagittarius A* supermassive black hole resides, the proximity of the cluster to the enormous black hole's powerful gravitational pull means that it shouldn't have much structure. 

But after investigation, researchers have discovered that the cluster's hot, massive stars are moving in an orderly pattern. Their explanation, outlined in a study published July 18 in The Astrophysical Journal, is that the stars are anchored by an elusive black hole that is interacting with Sagittarius A*. 

"This fascinating star cluster has continued to surprise the scientific community ever since it was discovered around twenty years ago," lead author Florian Peissker, an astronomer at the University of Cologne, in Germany, said in a statement. "At first it was thought to be an unusually heavy star. With the high-resolution data, however, we can now confirm the building-block composition with an intermediate-mass black hole at the centre."

Related: What would happen if a black hole wandered into our solar system?

Black holes are born from the collapse of giant stars and grow by gorging on gas, dust, stars and other black holes. Currently, known black holes tend to fall into two general categories: stellar-mass black holes, which range from a few to a few dozen times the mass of the sun, and supermassive black holes, cosmic monsters that can be anywhere from a few million to 50 billion times as massive as the sun.

Intermediate-mass black holes — which, theoretically, range from 100 to 100,000 times the sun's mass — are the most elusive black holes in the universe. While scientists have spotted evidence for several promising candidates, no intermediate-mass black holes have been definitively confirmed to exist.