We are seeing the glow from the stellar gas falling into the black hole," said Gezari
Using a bevy of telescopes, a team of astronomers led by Suvi Gezari of The Johns Hopkins University in Baltimore, Md. has identified that victim as a star rich in helium gas.
The star resided in a galaxy 2.7 billion light-years away-a light year being the distance light travels in a year-according to the team's results, to be published in the May 3 online edition of the journal Nature
"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.
We are seeing the glow from the stellar gas falling into the black hole over time," said Gezari
"We're also witnessing the spectral signature of the ejected gas, which we find to be mostly helium.
A spectral signature is a detailed breakdown by color of the light given off by some process; this can reveal which substances were present to begin with.
It's like "gathering evidence from a crime scene," Gezari
The observation also yields insights about the harsh environment around black holes and the types of stars swirling around them, she
team think the hydrogen-filled layers surrounding the star's core was lifted off a long time ago by the same black hole, explaining why there is only helium left.
The star may have been near the end of its life, the astronomers surmise.
After consuming most of its hydrogen fuel, it had likely ballooned in size, becoming a so-called red giant.
The astronomers think the bloated star was looping around the black hole in an elongated orbit, similar to a comet's around the sun.
On one of its close approaches, the star was stripped of its puffed-up atmosphere by the black hole's powerful gravity.
The stellar remains continued its journey around the center, until it ventured even closer to the black hole to face its ultimate demise.
Astronomers have predicted that stripped stars circle the central black hole of our Milky Way galaxy, Gezari
These close encounters are rare, occurring roughly every 100,000 years.
To find this one event, Gezari's
team monitored hundreds of thousands of galaxies in ultraviolet light with the Galaxy Evolution Explorer, a space-based observatory, and in visible light with the Pan-STARRS1 telescope on Mount Haleakala, Hawaii.
In June 2010, they spotted a candidate event with both telescopes.
They continued to monitor the flare as it reached peak brightness a month later, then slowly fadef over the next year.
"The longer the event lasted, the more excited we got, since we realized that this is either a very unusual supernova [stellar explosion] or an entirely different type of event, such as a star being ripped apart by a black hole," said team member Armin Rest of the Space Telescope Science Institute
By measuring the increase in brightness, the astronomers calculated the black hole's weight at roughly 3 million suns, which equals the weight of our Milky Way's black hole.
"The glowing helium was a tracer for an extraordinarily hot accretion [infalling] event," Gezari
"These observations also give us clues on what evidence to look for in the future to find this type of event," Gezari