Milky Way's black hole seen vaporizing asteroids

Posted by Kate Taylor

The supermassive black hole known as Sagittarius A has been observed emitting X-ray flares, lasting a few hours, about once a day.

"People have had doubts about whether asteroids could form at all in the harsh environment near a supermassive black hole," says Kastytis Zubovas of the University of Leicester.

"It's exciting because our study suggests that a huge number of them are needed to produce these flares."

The team suggests there is a cloud around Sagittarius A containing trillions of asteroids and comets, stripped from their parent stars. Asteroids coming within about 100 million miles of the black hole would be torn into pieces by its tidal forces, and then vaporized by friction, producing a flare.

"An asteroid's orbit can change if it ventures too close to a star or planet near Sgr A," says co-author Sergei Nayakshin, also of the University of Leicester. "If it's thrown toward the black hole, it's doomed."

Only asteroids larger than about six miles in radius could generate the flares observed by Chandra - although smaller asteroids are almost certainly being consumed too.

These results reasonably agree with models estimating of how many asteroids are likely to be in this region, assuming that the number around stars near Earth is similar to the number surrounding stars near the center of the Milky Way.

Planets thrown into orbits too close to the black hole would also be disrupted by tidal forces - although this would happen infrequently because planets aren't that common. However, it might be what caused a previous X-ray brightening of Sagittarius A by about a factor of a million about a century ago, causing an X-ray 'light echo' to reflect off nearby clouds.

"This would be a sudden end to the planet's life, a much more dramatic fate than the planets in our solar system ever will experience," saysZubovas.