For the first time, astronomers have identified a stellar victim of a giant black hole, an
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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. Astronomers 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. Astronomers say supermassive black holes rip apart stars very rarely, maybe just once every 10,000 years per galaxy. To detect one such event, Suvi Gezari of the Johns Hopkins University 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.The team was looking for a bright flare in ultraviolet light from the nucleus of a galaxy with a previously dormant black hole. Both telescopes spotted one in June 2010. Astronomers continued to monitor the flare as it reached peak brightness a month later and slowly faded during the next 12 months. The brightening event was similar to the explosive energy unleashed by a supernova, but the rise to the peak was much slower, taking nearly one and a half months. By measuring the increase in brightness, the astronomers calculated the black hole’s mass to be several million suns, which is comparable to the size of our Milky Way’s black hole. Spectroscopic observations with the Multiple Meter Telescope Observatory on Mount Hopkins in Arizona showed the black hole was swallowing lots of helium. Spectroscopy divides light into its rainbow colors, which yields an object’s characteristics, such as its temperature and gaseous makeup. To completely rule out the possibility of an active nucleus flaring up in the galaxy, the team used NASA’s Chandra X-ray Observatory to study the hot gas. Chandra showed that the characteristics of the gas didn’t match those from an active galactic nucleus.