Black Holes Regularly Eject Planet-Sized 'Cosmic Spitballs'

Artist's conception of a black hole spitballing planet-sized fragments into the galaxy. (Photo: Harvard/CFA)

Asteroids, comets, solar flares, rogue stars. There are all sorts of objects cruising through space that could one day end life as we know it on Earth. The most unusual and unexpected villain, however, may come from a 27 million-mile-wide black hole residing in the center of our galaxy.

Scientists studying this supermassive black hole, known as "Sagittarius A*" (or Sag A*) have discovered that it occasionally spitballs planet-sized objects to the farthest corners of the galaxy. Called tidal disruption and thought to happen every 10,000 to 1 million years, the process occurs when a star gets pulled into Sag A* and violently ripped apart. While much of its mass is sucked into the black hole's gaping maw, some manages to escape and settle into planet-sized fragments. These extremely hot objects are then ejected into space at speeds approaching more than 20 million miles per hour.

At a recent winter meeting of American Astronomical Society, researchers presented a simulation of how some of these objects, estimated to number at more than 100 million, could in fact one day come perilously close to our solar system. This video, created by Harvard undergraduate Eden Girma, shows our sun in relation to the black hole. Simulated over 10 billion years, it shows the outward projection of fragments from 50 devoured stars.

According to Girma's calculations, the closest of these planet-sized fragments from Sag A* would come within a few hundred light-years of Earth. While that might appear a safe distance, this simulation only accounts for the supermassive black hole at the center of our galaxy. Other black holes in other galaxies are also capable of flinging gigantic objects in our direction.

"Other galaxies like Andromeda are shooting these 'spitballs' at us all the time," co-author James Guillochon of the Harvard-Smithsonian Center for Astrophysics told

As for spotting these spitballs, while the objects give off heat from their violent formation, it's not enough to be detected by current space-based telescopes. The hope is that this may change with the arrival of future, more-sensitive instruments like the James Webb Space Telescope. If possible, they may provide useful information on the formation and composition of stars.

“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,” Girma told NatGeo.