SN 2008D close to generating a gamma-ray burst

Jul 25, 2008 10:51 GMT  ·  By
Image showing NGC 2770 and the supernova explosions SN 2007uy and SN 2008D (in the northern tip of the galaxy)
   Image showing NGC 2770 and the supernova explosions SN 2007uy and SN 2008D (in the northern tip of the galaxy)

SN 2008D, a supernova explosion detected by NASA's Swift X-ray Space Telescope inside the galaxy NGC 2770 on January 9, 2009, might have actually been triggered by the gravitational collapse of a massive star into a black hole, say researchers from the Max Planck Institute for Astrophysics, who claim that the event looked more like an energetic gamma-ray burst, rather than a classic stellar explosion.

"Our observations and modeling show this to be a rather unusual event, to be better understood in terms of an object lying at the boundary between normal supernovae and gamma-ray bursts," said the Italian astrophysicist Paolo Mazzali of the Padova Observatory and Max-Planck Institute for Astrophysics.

Stars having masses more than eight times that of the Sun, live their lives relatively fast, some of which expending all their fuel after only 100 million years, as compared to the star of our solar system which has been shining light for the last 5 billion years and is predicted to continue to do so for the next 5 billion, before turning into a red supergiant and finally into a white dwarf. By contrast, massive stars tend to create neutron stars and even black holes, if by the time of the supernova explosions they still have enough mass.

As they collapse under the action of the gravitational forces, massive stars emit energetic forms of light, such as X-ray and gamma-rays. While studying how the SN 2008D supernova behaved in its first stages, Mazzali discovered that the event was much more energetic than a typical stellar explosion, but still not powerful enough to generate a gamma-ray burst.

By extrapolating the results of his original findings, Mazzali then calculated that the star would have had an original mass about 30 times that of the Sun, but before the explosion more than two thirds of this mass was ejected into space. Although the amount of hydrogen and helium shed prior to the collapse of the core should have been enough to determine a gamma-ray burst, the presence of helium signatures in the supernova remnant indicate that such an event never took place.

Previous explanations proposed for the detection of X-ray bursts following the supernova event suggested that these energetic wavelengths were only visible because the explosion was detected as it occurred.