6degrees Astroblog
Astronomers Capture First-Ever Blast From Dying Star
By Irwin Horowitz, 5-21-08
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A team of astronomers today announced the first-ever observation of a massive star at the moment of its death. The star was located in the galaxy NGC 2770 in the constellation Lynx at a reported distance of about 88 million light years. The observation was a serendipitous occurrence as two members of the team were observing the decay of another supernova in this galaxy using NASA’s Swift gamma-ray satellite.
On 09 Jan 2008, Alicia Soderberg and Edo Berger from Princeton University were using the Swift telescope to observe SN2007uy when they noted a rapid burst in the x-ray emission from this galaxy. The burst lasted about five minutes before fading away. Both researchers recognized that something unusual had just occurred and quickly informed the astronomical community of their discovery.
A rapidly organized observing campaign employing the Hubble Space Telescope, the Chandra X-ray Observatory, the Swift satellite and a host of other facilities soon determined that the burst observed on that date was caused by the initial “break-out” of a supernova explosion, an event that had never previously been recorded. This object has since been labeled SN2008D.
Until now, all supernovae have first been observed as a result of their rapidly increasing optical brightness. However, due to opacity effects in the atmosphere of the exploding star, this optical light burst is delayed several hours after the actual moment when the shock wave blasts apart the outer layers. For decades, theoretical models of core-collapse supernovae suggested that x-rays and gamma rays should follow immediately behind the shock wave to be observable within moments of breaking free from the star. This is because these more energetic emissions are less affected by the opacity of the star.
An independent team of astronomers from UC Berkeley, led by postdoctoral researcher Maryam Modjaz were observing NGC 2770 at the same time and noted the initial optical burst a few hours after the x-ray burst detected by Swift. Based on the combined observations taken at all wavelengths, astronomers estimate that the progenitor star was born several million years ago with more than 30 times the mass of our Sun. It had shed most of its hydrogen envelope during its brief lifetime, leaving behind an exposed helium atmosphere.
In a statement released by Princeton University, Soderberg said “For years, we have dreamed of seeing a star just as it was exploding. We were in the right place, at the right time, with the right telescope, on January 9th and witnessed history.” The detection of the x-ray burst was facilitated by some special features of the Swift satellite, including the real-time data readout, wide field of view and numerous instruments. The results of their research are published in the 22 May 2008 issue of the science journal Nature.
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