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  Dim Supernova sheds light on Gamma-Ray Bursts

Dim Supernova sheds light on Gamma-Ray Bursts

Stars of more than eight solar masses normally end their lives in tremendous explosions known as supernovae. The exploding star then shines as brightly as billions of stars together, and in a short time releases more energy than the Sun during its entire life span of 10 billion years. However, the final fate of some massive stars is less spectacular: dim supernovae are a hundred times less energetic and much less luminous. Researchers of the Queen's University Belfast, the Italian National Institute for Astrophysics and the Max Planck Institute for Astrophysics have now for the first time discovered a dim supernova whose spectrum shows no trace of hydrogen. This may solve a long-standing mystery about certain cosmic gamma-ray bursts. (Nature, 2009 June 4)

Fig.: SN 2008ha (marked by an arrow) turned out to be the prototype of a new kind of supernovae. It exploded in an irregular galaxy at a distance of 67 million light years. The picture was taken with the 2.2m Telescope of the Calar Alto Observatory in southern Spain.

Astronomers are excited about the lack of hydrogen in the supernova, named SN 2008ha, as it indicates that the progenitor star must have lost its entire outer hydrogen-rich layers prior to the explosion. There are two possibilities to accomplish this: interaction in a binary system with strong mass transfer to a companion star, or vigorous stellar winds which have blown the progenitor's envelope into space.

The second scenario can only work for very massive stars. The collapsing core of such a star would then form a black hole, which would swallow the majority of the radioactive material synthesised in the supernova. Indeed, the astronomers have found very little radioactive material in the ejecta of SN 2008ha.

If the model involving the very massive star proves true, SN 2008ha is particularly important for understanding the relationship between supernovae and a group of "long" cosmic gamma-ray bursts (where "long" refers to the gamma-ray emission lasting for several seconds). For more than a decade, astronomers have believed that all these long bursts are associated with powerful supernova explosions. However, in recent years, two long gamma-ray bursts have been detected which were not accompanied by such energetic and luminous supernovae. This gave rise to the speculation that they might have been associated with dim supernovae which evaded detection.

The problem: up to now only hydrogen-rich dim supernovae have been known, and these are not suitable candidates, since the extended hydrogen envelopes of their progenitor stars would prevent the formation of a gamma-ray burst. "The existence of hydrogen-deficient dim supernovae like SN 2008ha could now help to solve this puzzle", says Stefan Taubenberger, researcher at the Max Planck Institute for Astrophysics in Garching and co-author of the article in Nature.


Stefano Valenti, Andrea Pastorello, Enrico Cappellaro, Stefano Benetti, Paolo Mazzali, Jose Manteca, Stefan Taubenberger, Nancy Elias-Rosa, Rafael Ferrando, Avet Harutyunyan, Veli-Pekka Hentunen, Markku Nissinen, Elena Pian, Massimo Turatto, Luca Zampieri, Stephen J. Smartt, "A low energy core-collapse supernova without a hydrogen envelope", Nature, 4. Juni 2009

For more information, please, contact:

Dr. Stefan Taubenberger
Max Planck Institute for Astrophysics
Phone: +49 89 30000-2297
Fax: +49 89 30000-3569

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