Out-of-control stars reveal hidden black holes among the galaxy’s closest neighbors

Astronomers have discovered strong evidence of the closest supermass black hole outside the Milky Way. This huge black hole is located in the large Magellan cloud, one of our own closest galactic neighbors.

To make this discovery, researchers tracked the roads with 21 stars of ultra-fine precision in the suburbs of the Milky Way. These stars travel so fast that they will escape the gravitational clutch of the Milky Way or nearby Milky Way. Astronomers call it “speeding” star.

Similar to how forensic experts reproduce the origins of bullets based on their trajectory, researchers identified the origins of these speeding stars. They found that about half of them were related to supermassive black holes in the center of the Milky Way. However, the other half originated elsewhere: giant black holes previously unknown in the Large Magellan Cloud (LMC).

“It’s shocking to be cosmic, we have another supermassive black hole below the block,” said Jesse Han of the Center for Astrophysics | Harvard and Smithsonian who lead the new research. “Black holes are so secretive that this is almost always under our noses.”

Researchers discovered this secret black hole by using data from the European Space Agency Gaia Mission is a satellite that tracks over a billion stars throughout the Milky Way with unprecedented accuracy. They also used improvements to the recently obtained galaxy orbits of LMC orbits, which other researchers recently obtained.

“We know these high-speed-level stars have been around for a while, but Gaia gives us the data we need to figure out where they really come from,” said Kareem El-Badry, co-author of the Caltech Institute in Pasadena, California. “By combining this data with our new theoretical model to enable the way these stars move, we have made this extraordinary discovery.”

High-speed stars are created when the binary star system ventures too close to a supermass black hole. The strong gravity of the black hole tear apart two stars, capturing one into the surrounding near-orbit. Meanwhile, another orphan star was abandoned at more than millions of miles per hour, and the speeding star was born.

A major study by the team is predicting through its theoretical model that a supermassive black hole in the LMC will create a group of high-speed stars in one corner of the Milky Way because of the way the LMC moves around the Milky Way. Stars popping up along the direction of LMC motion should get extra speed. In fact, their data reveals the existence of such clusters.

The team found that the properties of superspeed stars cannot be explained by other mechanisms, for example, when a companion experiences a supernova explosion or a star is ejected by the above-mentioned star, and the star is ejected by the mechanism described above as a binary star system, but without super-large black holes.

“The only explanation we can propose for these data is the existence of a monster black hole in the Milky Way next door,” said Scott Lucchini, also co-author of CFA. “So, in our cosmic community, it’s not just the supermassive black holes of the Milky Way that drive away stars from their galaxy.”

Using the speed of stars and the relative number of popped up by LMC and the Milky Way super black hole, the team determined that the mass of the LMC black hole is about 600,000 times the mass of the sun. For comparison, supermassive black holes in the Milky Way have about 4 million solar power. Elsewhere in the universe, there are supermassed black holes that are billions of times higher than the Sun.

A paper describing these results has been accepted for publication in the journal Astrophysics and is available here.