Monster Black Hole Caught Swallowing Unlucky Star

by Charles Q. Choi, SPACE.com Contributor

Date: 02 May 2012 Time: 01:01 PM ET

This computer-simulated image shows gas from a tidally shredded star falling into a black hole. Some of the gas also is being ejected at high speeds into space. CREDIT: NASA, S. Gezari (The Johns Hopkins University, Baltimore, Md.), A. Rest (Space Telescope Science Institute, Baltimore, Md.), and R. Chornock (Harvard-Smithsonian Center for Astrophysics, Cambridge, Ma.)  View full size image

Call it a Cosmic Scene Investigation: For the first time, scientists have identified a stellar victim of a giant black hole — an unlucky star whose death may ultimately provide more clues on the inner workings of the enigmatic gravitational monster that devoured it.

Supermassive black holes are objects millions to billions times the sun's mass that lurk in the hearts of most galaxies. They lay quietly until victims, such as stars, wander close enough to get shredded apart by their extraordinarily powerful gravitational pull.

Scientists first caught a black hole red-handed in a stellar murder last year. Now researchers have determined not only the culprit in a similar cosmic homicide but the casualty as well: a star rich in helium gas.

"This is the first time we've actually been able to pinpoint what kind of star was disrupted," study lead author Suvi Gezari, an astronomer at Johns Hopkins University, told SPACE.com. [Photos: Black Holes of the Universe]

Hungry black holes

Astronomers say supermassive black holes rip apart stars very rarely, maybe just once every 10,000 years per galaxy. To detect one such event, Gezari and her colleagues monitored hundreds of thousands of galaxies in ultraviolet light with the space-based Galaxy Evolution Explorer (GALEX) and in visible light with the Hawaii-based Pan-STARRS telescope.

In June 2010, the researchers spotted a bright flare from the previously dormant black hole at the center of a galaxy approximately 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."

The flare of light reached peak brightness a month after it was detected, then slowly faded over the next 12 months. By measuring the rise of the flare's brightness, the scientists calculated the rate at which the star's gas was getting sucked into the black hole. This in turn helped reveal at what point and time the black hole had begun disrupting the star, revealing how powerful its gravitational field was and thus its mass.

The astronomers estimate the black hole's mass to be 3 million suns, comparable to  our Milky Way's central black hole.

"These spectacular events provide a glimpse into otherwise unobservable black holes, telling us about their masses," Gezari said. "We know that there are strong connections between black holes and the galaxies they reside in, and it turns out that somehow the mass of the black hole and the mass of a galaxy influence each other, so we want to better know what's going on there. Also, people want to understand the physics of black holes and how they affect the geometry of space-time around them. We need to know its mass to help pinpoint a lot of those details.
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