From the July 2012 issue

Feeding frenzy of a supermassive black hole

A galaxy’s central black hole roars to life when a normal star ventures too close.
By | Published: July 23, 2012
The center of the Milky Way Galaxy harbors a supermassive black hole with a mass some 4 million times that of the Sun. The region immediately surrounding its event horizon — the radius at which a beam of light would just fail to escape the object’s gravitational clutches — is currently pretty empty. Without much material, the black hole remains fairly quiet, at least when compared with the supermassive black holes in some other galaxies.

But this won’t always be the case. Black holes shine brightly, particularly in X-rays and radio waves, when they devour nearby objects. In this video, a Sun-like star nears a supermassive black hole located in the center of a galaxy. As the star approaches, the black hole’s intense gravity distorts the star. Tidal forces tear off the part of the star closest to the invisible object. This material streams toward the black hole and forms an accretion disk around it while the rest of the star simply dissipates into space. The captured material moves faster and faster, and friction among the atoms heats it to millions of degrees. Meanwhile, magnetic fields channel some of the gas into high-speed jets that escape along the black hole’s rotational axis.

NASA’s Goddard Space Flight Center in Greenbelt, Maryland, created this video to show what happens when a supermassive black hole swallows a normal star. The simulation describes what astronomers think happened in a galaxy located some 3.9 billion light-years from Earth, which burst into X-ray and radio brilliance in 2011. But the same scenario almost certainly has played out in the Milky Way’s core in the past — and will do so again in the future.