Milky Way’s black hole may hurl galactic spitballs our way

Giant gas blobs are what’s left of gravity-shredded stars

illustration of Jupiter-sized gas blobs

DUCK! Blobs of gas roughly the mass of Jupiter (several illustrated) could form near the black hole at the center of the Milky Way and shoot into intergalactic space.

Mark A. Garlick/CfA

GRAPEVINE, TEXAS — The gargantuan black hole at the center of the Milky Way is a little like an unruly kid, hurling spitballs. But unlike a child’s arsenal, these spitballs are roughly the size of a planet and can travel fast enough to shoot out of the galaxy. Some might even zip right by our solar system.

Stars that pass too close to the black hole can be shredded by the intense gravity. Previous simulations have shown that within these strands of stellar debris, gas can clump back together into balls roughly the mass of Jupiter that are then launched away at several thousand kilometers per second. What happens to these blobs was unknown.

About 95 percent are launched so fast that they escape the gravity of the Milky Way and fly into intergalactic space, Eden Girma, an undergraduate at Harvard University, said January 6 in a news conference at a meeting of the American Astronomical Society. Girma and James Guillochon, an astrophysicist at the Harvard-Smithsonian Center for Astrophysics, developed computer simulations to figure out the fate of these galactic spitballs. Those that don’t escape get stuck in orbits just a few hundred light-years from the black hole.

Of those that do fly away, some could pass through our cosmic neighborhood, getting as close as about 700 light-years, said Girma. Detecting them won’t be easy. With no internal heat source, the blobs would emit only a trickle of infrared light. The best bet, she said, is to catch one as it passes between Earth and a distant star. The starlight, magnified by the gravity of the projectile, would momentarily brighten and betray the blob’s presence.

Christopher Crockett is an Associate News Editor. He was formerly the astronomy writer from 2014 to 2017, and he has a Ph.D. in astronomy from the University of California, Los Angeles.

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