domingo, 17 de fevereiro de 2008

Researchers Find a Supernova, Before it Exploded

Written by Fraser Cain
SN 2007on. Image credit: Chandra
The problem with supernovae is that you never know where they're going to happen. Your only clue is the bright flash in the sky, and then it's too late. But a team of European researchers think they were lucky enough to have spotted the precursor to supernova.

In an article in the February 14th issue of the journal Nature, a team of European researchers describe how they were trying to find evidence of a binary system after one of the objects detonated as a supernova. In looking back through archived images captured by NASA's Chandra X-Ray Observatory, they were lucky enough to find one image that actually contained the system.
The supernova, known as SN 2007on exploded as a Type Ia. This is the situation where a white dwarf is in orbit around another star. It's possible that the white dwarf feeds off material ejected from the other star until it hits a critical amount of mass - approximately 1.4 times the mass of our Sun. Or maybe it's actually a collision between a white dwarf and another star, or between two white dwarfs.
Whatever the condition, the result is always the same. The white dwarf detonates suddenly with a very specific amount of energy and characteristic light curve. Astronomers use these explosions to measure distance in the Universe, since they're always exploding with the same amount of energy.
To really figure out what's going on, astronomers need more examples of these precursors. They need to be able to study a potential Type Ia supernova before it actually explodes.
So, the researchers finally have a target they can study. In the case of SN 2007on, the data gathered by the Chandra X-Ray Telescope strengthens the "mass stealing" theory. X-rays streaming from the system show the kind of fusion you would expect from a white dwarf consuming material from a neighbour.
This isn't a slam dunk, though. A higher-quality optical image shows the binary system to be in a slightly different position from where the supernova detonated. So maybe this system isn't the precursor after all.
But followup observations from Chandra show that the X-ray source is gone. Whatever was at that location isn't there any more. Perhaps it did indeed vaporize in a supernova explosion.

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