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Milky Way and Andromeda Galaxies Apparently Launch ‘Spitballs’ at Each Other

"A single shredded star can form hundreds of these planet-mass objects.”
Concept art of cosmic spitballs. Image: Mark A. Garlick/CfA

In the center of our Milky Way galaxy, 26,000 light years from Earth, lives a supermassive black hole called Sagittarius A*. Its mass, equivalent to about four million Suns, is stuffed entirely behind an event horizon stretching across eight million miles, smaller than the distance between Mercury and the Sun. Needless to say, it is a pretty weird place, so it should be no surprise that it exhibits weird behavior.


Still, chewing up stars and spitting out their remains in the form of planet-sized gas balls traveling at insane speeds? That's kooky even for you, Sagittarius A*. But new research presented this week at the 2017 American Astronomical Society meeting demonstrates that the Milky Way's black hole may genuinely play this game of "cosmic spitball," as researchers described it.

Here's how it goes down, according to lead author Eden Girma, a Harvard University undergraduate student and Banneker/Aztlán Institute member: Every 10,000 years or so, an unlucky star ventures too close to Sagittarius A*, falls into its deadly tidal embrace, and gets torn to shreds.

Sagittarius A* region. Image: NASA/CXC/MIT/F. Baganoff, R. Shcherbakov et al.

Over the course of 50 simulations of these interactions, Girma and her mentor, Harvard astrophysicist James Guillochon, observed that the ripped-up chunks of star stuff can coagulate into gas balls ranging in size from Neptune-scale objects to worlds many times larger than Jupiter. The extreme environment of the black hole catapults these balls into space at speeds of 20 million miles per hour, so fast they can escape the galaxy entirely.

"A single shredded star can form hundreds of these planet-mass objects," Girma said in a statement. A whopping 95 percent of the simulated objects were flung into intergalactic space, perhaps reaching neighboring galaxies like Andromeda. Likewise, Guillochon said, Andromeda's supermassive black hole may be launching similar stellar projectiles back at the Milky Way. "Other galaxies like Andromeda are shooting these 'spitballs' at us all the time," he noted.

The remainder of the objects were either locked in orbit around Sagittarius A*, or migrated to the outer regions of the Milky Way. Some of them of them may be within a few hundred light years of Earth.

READ MORE: Earth-Sized Telescope Bags Magnetic Fields from the Milky Way's Black Hole Core

At the moment, nobody has actually produced a hard visual on any of these objects, but next generation observatories like the Large Synoptic Survey Telescope and James Webb Space Telescope may be equipped to spot them. Until then, it's enough to add "forging stellar spitballs in supermassive black holes" to the list of the universe's most bizarre hijinx.

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