The Large Magellanic Cloud floats in space, in a long and slow dance around our galaxy. Vast clouds of gas within it slowly collapse to form new stars. In turn, these light up the gas clouds in a riot of colors.
The Large Magellanic Cloud, photographed here by the Hubble Space Telescope, is about 160,000 light-years from Earth.
Astronomers may have just solved an intergalactic “whodunit.” Researchers traced the trajectories of super speedy stars all the way back to their sources—and they discovered strong evidence of a previously unknown supermassive black hole just outside our home galaxy.
“It is astounding to realize that we have another supermassive black hole just down the block, cosmically speaking,” Jesse Han, an astronomer from the Center for Astrophysics, Harvard and Smithsonian, who led a new study of these stars, says in a statement. “Black holes are so stealthy that this one has been practically under our noses this whole time.”
The fast-moving stars in question are called “hypervelocity” stars—and they’re thought to have enough speed to escape the gravity of our galaxy. Astronomers suggest that supermassive black holes create hypervelocity stars when binary stars (a pair of stars gravitationally bound to each other) get too close.
“The intense gravitational forces tear the pair apart,” Han explains to Reuters’ Will Dunham. “One star is captured into a tight orbit around the black hole, while the other is flung outward at extreme velocities—often exceeding thousands of kilometers per second—becoming a hypervelocity star.”
Using data from the European Space Agency’s Gaia mission, which is mapping stars in and around the Milky Way, the researchers determined the origin of 21 hypervelocity stars on the edge of our galaxy. They found that half were associated with the supermassive black hole at the center of our Milky Way, called Sagittarius A*. The other half seemed to be linked to a supermassive black hole at the center of the Large Magellanic Cloud (LMC), a neighboring dwarf galaxy thought to be orbiting the Milky Way.
There’s just one caveat. Astronomers didn’t know the LMC had a supermassive black hole. The LMC is one of the most studied galaxies, and yet the team’s work provides the first evidence of a supermassive black hole in its center, Han tells Forbes’ Bruce Dorminey. Their findings were published on arXiv as a preprint study that’s been accepted for publication in The Astrophysical Journal.
Artist’s rendition of a hypervelocity star ejected from the LMC. The original binary’s orbital path is shown as interwoven lines, with one star being captured by the black hole (near center of inset) while the other is ejected into space (lower right).
Artist’s rendition of a hypervelocity star ejected from the LMC. The original binary’s orbital path is shown as interwoven lines, with one star being captured by the black hole (near center of inset) while the other is ejected into space (lower right).
If confirmed, the new discovery would make this the closest supermassive black hole outside of our galaxy. In a theoretical model, the team predicted that a supermassive black hole in the LMC would create hypervelocity stars and place them on the edge of our galaxy. Their data showed the same thing.
“The only explanation we can come up with for this data is the existence of a monster black hole in our galaxy next door,” study co-author Scott Lucchini, an astrophysicist at the Center for Astrophysics, Harvard and Smithsonian, says in the statement. “So, in our cosmic neighborhood it’s not just the Milky Way’s supermassive black hole evicting stars from its galaxy.”
Though no one had spotted evidence of this black hole before, its existence is no surprise. Considering the mass and structure of the LMC, astronomers would expect it to host a supermassive black hole, as Han tells Reuters. The finding, he adds, “really does make sense.”
According to the team’s calculations, the mass of the LMC’s supermassive black hole is 600,000 times that of the sun. While that might sound huge, the newly identified supermassive black hole has a much lower mass than others. Sagittarius A*, for example, has four million times the sun’s mass, and other supermassive black holes reach billions of solar masses, per the statement.
The study is a powerful reminder that we still have a lot to discover about even the most well-known corners of space.
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Margherita Bassi | READ MORE
Margherita Bassi is a freelance journalist and trilingual storyteller. Her work has appeared in publications including BBC Travel, Discover magazine, Live Science, Atlas Obscura and Hidden Compass.
Filed Under: Astronomy, Astrophysics, Black Holes, Center for Astrophysics, Harvard and Smithsonian, New Research, Outer Space, Smithsonian, Smithsonian Institution