'The Planetary Spitball Machine' --Milky Way's Supermassive Black Hole Spews Out Millions of Star Fragments --"Large as Jupiter and Neptune"
New simulations from Harvard University undergraduate Eden Girma and her mentor, James Guillochon, an Einstein fellow at the Harvard-Smithsonian Center for Astrophysics, presented January 4 at the American Astronomical Society’s annual meeting in Texas, suggest that our galaxy’s massive black hole could be responsible for sending an astronomical amount of these free-floating objects zipping through space.
“Our galaxy could be populated by hundreds of millions of these cold fragments that are the direct remnants of stars,” Girma says.
Every 10,000 years or so, a star wanders too close to Sagittarius A* shown below, the supermassive black hole parked in the center of the Milky Way and the black hole’s intense gravity disrupts and shreds the star, leaving streamers of gas strewn near the Milky Way’s heart.
Girma and Guillochon simulated 50 star-shredding encounters and watched as that noodly, disrupted starstuff began to reconnect, balling itself up and forming planet-mass clumps of gas and dust. “While tidal disruptions in the galactic center have been a subject of research since the late ‘80s, the idea that actual compact objects could form from this process is very new,” Girma says.
In their simulations, some 11,473 planetoids grew out of the star remnants —each more massive than Neptune, and sometimes many times larger than Jupiter zooming into outer space at speeds exceeding 20 million miles an hour.
Of those newly born objects about 95 percent were flung from the galaxy out into the outer spiral arm hinterlands. A much smaller percentage remained bound to Sagittarius A*, destined to endlessly circle the dark monster that ripped the original star apart. The smallest set of planetoids, fewer than one percent of the total, are now wandering the outskirts of the Milky Way, perhaps within about six hundred light-years of Earth.
It's an interesting and plausible scenario, says UCLA's Andrea Ghez, an expert on the antics of Sagittarius A*.
If Girma and Guillochon are right about how frequently Sagittarius A* shreds passing stars, she told National Geographic, "then there could be millions of these strange almost-planets in the Milky Way. Still more could be interlopers from our neighboring galaxies, punted into space by their central black holes in an epic game of intergalactic pinball."
“In general, these fragments travel at extremely high speeds and can escape the galaxy completely,” Girma says. This raises the question: How many of the stellar fragments wandering through the Milky Way were actually created in other galaxies?
Whether we’d know one of these planetary spitballs when we see one is still up for debate. Without a star to call their own, the planetoids cool to a temperature that makes finding them a task for infrared eyes. And even then, they wouldn’t necessarily be festooned with a fingerprint advertising a stellar or extragalacYet, Girma says,
“in detecting them we could then delve more deeply into the chemical composition of these fragments, learning more about the star it originated from and perhaps determining their own habitability,” concludes Girma.
The major difficulty is actually attempting to find these objects as, given the vastness of space, our telescopes will find it extremely difficult to spot cold objects that aren’t on the infrared spectrum.