Computer simulation shows gas from a shredded star falling into a black hole. Some of the gas also is being ejected at high speeds into space.
Like intergalactic crime scene investigators, scientists have for the first time identified an unlucky star shredded by a supermassive black hole.
Nasa's Galaxy Evolution Explorer, a space-based observatory, and the Pan-STARRS1 telescope on the summit of Haleakala in Hawaii were among the first to help identify the stellar remains.
Supermassive black holes, weighing millions to billions times more than the sun, lurk in the centers of most galaxies. Any unsuspecting victim, such as a star, that wanders close enough, is destroyed by the supermassive black hole's powerful gravitational forces.
These images show a brightening inside a galaxy caused by a flare from its nucleus. The arrow in each image points to the galaxy. The flare is a signature of the galaxy's central black hole shredding a star that wandered too close. The top left image, taken by the Galaxy Evolution Explorer in 2009, shows the galaxy's location before the flare. The galaxy is not visible in this ultraviolet-light exposure. In the top right image, taken by the Galaxy Evolution Explorer on June 23, 2010, the galaxy has become 350 times brighter in ultraviolet light. The bottom left image, taken by Pan-STARRS1, shows the galaxy (the bright dot in the center) in 2009 before the flare's appearance. The bottom right image, taken by Pan-STARRS1 from June to August 2010, shows the flare from the galaxy nucleus. Note how the light from the flare is much bluer, or hotter, than the host galaxy light.
A team of astronomers led by Suvi Gezari of the Johns Hopkins University, Baltimore, Maryland, identified the victim as a star rich in helium gas, resident in a galaxy 2.7 billion light-years away.
"When the star is ripped apart by the gravitational forces of the black hole, some part of the star's remains falls into the black hole, while the rest is ejected at high speeds," Gezari said. "We are seeing the glow from the stellar gas falling into the black hole over time. We're also witnessing the spectral signature of the ejected gas, which we find to be mostly helium. It is like we are gathering evidence from a crime scene. Because there is very little hydrogen and mostly helium in the gas, we detect from the carnage that the slaughtered star had to have been the helium-rich core of a stripped star."
The supermassive black hole damaged the star as it orbited before finally swallowing its remains, the astronomers say.
The star's hydrogen-filled envelope surrounding the core was first lifted off. After consuming most of its hydrogen fuel, it had probably ballooned in size, becoming a red giant.
After the star was stripped of its puffed-up atmosphere by the black hole's powerful gravity, the stellar remains continued its journey around the centre, until meeting its end at the centre of the black hole.
Astronomers predict stripped stars circle the central black hole of our Milky Way galaxy. These close encounters are rare, occurring roughly every 100,000 years.