Speedy Stars Uncover Supermassive Black Hole in Neighboring Galaxy

WASHINGTON—The Large Magellanic Cloud, a dwarf galaxy located near our Milky Way, appears to the naked eye as a shining patch of light from the southern hemisphere of Earth. It is named after the Portuguese explorer Ferdinand Magellan, who first documented it five centuries ago. Recent research is shedding new light on the composition of this galactic neighbor.

Analysis of the paths of nine rapidly moving stars at the outskirts of the Milky Way presents compelling evidence for the presence of a supermassive black hole within the Large Magellanic Cloud. While most galaxies are believed to harbor such a black hole at their center, this marks the first clear evidence of one existing in the Large Magellanic Cloud.

The trajectory data suggests these stars were expelled from the Large Magellanic Cloud following a violent encounter with this black hole. Black holes are extremely dense entities with gravitational forces so intense that even light cannot escape their grasp.

Situated approximately 160,000 light-years away from Earth, the Large Magellanic Cloud is one of the closest galaxies to the Milky Way. This makes its supermassive black hole the nearest to us, aside from Sagittarius A*, or Sgr A*, which resides at the center of the Milky Way and is about 26,000 light-years from Earth. A light-year is the distance light travels in a year, approximately 5.9 trillion miles.

While the Milky Way is significantly more massive than the Large Magellanic Cloud, Sgr A* is also vastly more massive than the newly discovered black hole, which is among the least massive of known supermassive black holes. Sgr A* has a mass roughly 4 million times that of the sun, whereas the newly identified black hole has a mass around 600,000 times greater than the sun’s.

In contrast, some supermassive black holes identified in larger galaxies dwarf Sgr A*. For instance, one detected in the galaxy Messier 87 has a mass 6.5 billion times that of the sun. Only Sgr A* and this black hole have ever been directly imaged by astronomers.

The latest study centered on hypervelocity stars, which are created when a binary star system—two stars bound together by gravity—approaches a supermassive black hole too closely.

“The immense gravitational pull disrupts the binary system. One star becomes trapped in a tight orbit around the black hole, while the other is ejected at incredible speeds—often exceeding thousands of kilometers per second—transforming into a hypervelocity star,” explained Jesse Han, a doctoral candidate in astrophysics at Harvard University and the primary author of the study published in the Astrophysical Journal and released to the public on Thursday.

The sun orbits through space at approximately 450,000 miles per hour, but hypervelocity stars exceed that speed by several times.

The researchers utilized data from the European Space Agency’s Gaia observatory, which has meticulously tracked over a billion stars in our galaxy with an unprecedented level of precision.

Currently, there are 21 recognized hypervelocity stars within the Milky Way. Astronomers have successfully traced the origins of 16 of these stars, with seven linked to Sgr A* at our galaxy’s center and the other nine tracked back to the Large Magellanic Cloud.

“The only plausible explanation is that the Large Magellanic Cloud contains a supermassive black hole at its center, similar to Sgr A* in our galaxy,” Han stated.

“Given the mass and structure of the Large Magellanic Cloud, it is completely expected to have a supermassive black hole of this size. We just needed to gather the evidence to support it,” Han said. “It’s an exciting discovery that also aligns logically with our expectations.”

The nearest supermassive black hole outside the Milky Way prior to this study was the one within the Andromeda galaxy, located about 2.5 million light-years away, which is the closest major galaxy to the Milky Way.

“Despite the Large Magellanic Cloud being one of the most extensively studied galaxies, the existence of this supermassive black hole was only inferred indirectly by tracing the origins of swift-moving stars. We still have more work ahead to accurately locate the black hole,” remarked Caltech astronomer and co-author of the study, Kareem El-Badry.

By Will Dunham