Most powerful supernova ever observed may be the first of its kind ever seen
A recently-observed supernova is the most luminous one ever detected. ...
How big can a supernova get? Beyond the "big explosions are cool" aspect, the topic has some important scientific implications. Early in the life of the universe, when matter was more densely packed, it's believed that extremely large stars formed and exploded at a rapid clip. This both influenced the dynamics of the early galaxies and led to the distribution of heavier elements that have allowed things like our solar system to form. So, understanding the explosions of the earliest stars can help us comprehend the evolution of the universe. The problem, of course, is the conditions that produced the earliest stars have been uncommon for billions of years. The chances of observing one are correspondingly low. But we may have gotten lucky last year when SN 2006gy burst onto the scene. As described in a paper that will appear in the The Astrophysical Journal (draft available), it was a prodigious explosion: the most luminous supernova ever recorded, it took 70 days to reach peak brightness and a further 30 to fade back. During that time, it's estimated that SN 2006gy radiated 1051 erg. The explosion was so far beyond the norm that it was misidentified as a new active galactic nucleus. The authors also use some decidedly atypical language: "Simply put, for a supernova to be extremely luminous and to remain so for such an extended time is truly spectacular." Hard to argue. But why was this one so spectacular? Here, the authors consider a couple of unusual possibilities and reject them based on the observational data. Instead, they suggest a typical source of post-supernova energy: the decay of radioactive elements (primarily 56Ni) formed in the blast. Just more of it. Lots more, in fact: about 22 solar masses' worth. The problem with needing that much material is that it requires a supermassive star, which should undergo a core collapse into a neutron star or black hole. This should prevent a lot of the mass of the star from joining in on the explosive fun, thus cutting down on the total radiance. To get around this seeming contradiction, the authors suggest that SN 2006gy was the first ever example we've observed of what's called a pair-instability supernova, which requires a star weighing in at 100-150 solar masses. In these explosions, the density of gamma rays gets so high that the energy gets converted directly into mass. This process forms matter and antimatter in equal proportions, and the resulting interactions blow the core apart, allowing all of the star's mass to power the supernova. The authors note that there is a way to square a more traditional supernova with most (but not all) of the observational data. The alternative requires the parent star to have burped out several solar masses' worth of hydrogen over the preceding decades. Given that this is a rare event and requires an unusual parent star, they consider the chances of it occurring immediately prior to the supernova to be very remote. More important, perhaps, is the fact that the alternative combination also requires a parent star with a mass of well over 100 times that of the sun. So, in either case, SN 2006gy appears to represent the explosion of an exceptionally massive star; an event that has probably grown increasingly rare as the universe has aged. Expect the follow-up observations to provide a wealth of information. Pictures, animations, etc. are available at the Chandra site. Expand full story
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