Black hole caught in a feeding frenzy
Scientists were able to observe the demise of a star and its digestion by a previously dormant supermassive black hole in real time.
May 2, 2012
If a star passes too close to a black hole, tidal forces can rip it apart, and its constituent gases then swirl in toward the black hole. Friction heats the gases and causes them to glow. By searching for newly glowing supermassive black holes, astronomers can spot them in the midst of a feast.
These images, taken with NASA's Galaxy Evolution Explorer (GALEX) and the Pan-STARRS1 telescope in Hawaii, show a galaxy that brightened suddenly, caused by a flare from its nucleus. 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 GALEX in 2009, shows the galaxy before the flare, when it wasn't visible in ultraviolet light. In the top right image, taken by GALEX on June 23, 2010, the galaxy had 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 (hotter) than the host galaxy light. Credit: NASA/S. Gezari (JHU)/A. Rest (STScI)/R. Chornock (Harvard-Smithsonian CfA)
The team discovered just such a glow May 31, 2010, using the Pan-STARRS1 Telescope on Mount Heleakala in Hawaii. The flare brightened to a peak July 12 before fading away over the course of a year.
"We observed the demise of a star and its digestion by the black hole in real time," said Edo Berger from the Harvard Smithsonian Center for Astrophysics in Cambridge, Massachusetts.
The glow came from a previously dormant supermassive black hole at the center of a galaxy 2.7 billion light-years away. The black hole contains as much mass as 3 million Suns, making it about the same size as the Milky Way's central black hole.
Follow-up observations with the MMT Observatory in Arizona showed that the black hole was consuming large amounts of helium; therefore, the shredded star likely was the core of a red giant star. The lack of hydrogen showed that the star lost its outer atmosphere on a previous pass by the black hole.
"This star barely survived one encounter with the black hole, only to meet its unfortunate end in round two," said Chornock.
The discovery demonstrates the sleuthing power of the Panoramic Survey Telescope and Rapid Response System (Pan-STARRS), which was designed to locate all kinds of transient phenomena in the night sky.