An international research team from the University of Cologne recently discovered one of the rarest types of black holes in the world. Researchers observed a cluster of stars near a supermassive black hole called Sagittarius A (Sgr A) at the center of the Milky Way. They then discovered signs of an intermediate-mass black hole, a type of black hole known as the “missing ring” of black holes, according to NASA.

Black holes range in size from supermassive to primitive, with black holes in between being larger than primitive. These formed shortly after the Big Bang and are considered to be “seeds” for the formation of supermassive black holes.

The star cluster, thought to be a modern intermediate-mass black hole called IRS 13, was expected to be randomly positioned, but instead moved in a regular pattern. According to a statement from the University of Cologne, the researchers assume that the star cluster is interacting with a supermassive black hole and “there must be something in the star cluster to maintain the compact shape that I observed. That certainly must be happening.”

There are plans in the works for further observations of intermediate black holes. They will use the James Webb Space Telescope and the Very Large Telescope (yes, that’s its real name) in Chile, which is currently under construction.

Scientists discovered the first intermediate-mass black hole in 2020, using the Hubble Space Telescope to capture the ripples of its formation. Until then, intermediate-mass black holes are thought to be the “missing link” between stellar masses and supermassive black holes, potentially providing new insights into how black holes and the universe form.