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The star explosion missed by everybody |
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Written by Derek Kessler on
Tuesday, 22 July 2008
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 If a star explodes and nobody’s watching, does it light up? It’s not quite the tree in the forest quandary, but it’s a question to be asked nonetheless: what can we learn from novas that we missed? The ESA’s XXM-Newton x-ray telescope happened upon such an event late last year. The orbital observatory was turning to face a new target and passed over a bright source of x-rays that nobody had expected, seen, or cataloged, but was bright enough to be immediately noticeable.
Puzzled, the XXM-Newton team looked around that segment of the sky for a likely source and came up with three potential candidates. The astronomers sent out their findings to other astronomers world-wide, and it was the Magellan-Clay telescope at Las Campanas Observatory in Chile that found the answer. One of the stars, a nominally bright star designated USNO-A2.0 0450-03360039, was six hundred times brighter than it was the last time anybody had looked at it. That’s the difference between the faintest stars visible in urban skies and Venus, the brightest planet (apparent magnitudes 3 and -4, respectively). There was only one explanation for such a radical increase in brightness: the star had gone nova.
As opposed to a supernova, which is the explosion of a large dying star, novae are markedly different. They occurred when small compact white dwarf stars are pair with a larger companion star. The gravity of the white dwarf lets it siphon gas off the other star until it builds up to the point of nuclear reaction and subsequent explosion.
In these explosions, the x-rays that XXM-Newton detected typically aren’t seen for many days until afterwards, as the cloud of debris created tends to mask them. As the cloud dissipates, x-rays become visible (to proper equipment, like XXM-Newton, of course). In the meantime, the nova should have been easily visible with the naked eye on Earth, but nobody reported seeing it.
To confirm, the All Sky Automated Survey project looked at their observations from nights prior to XXM-Newton’s detection, and sure enough, on June 5, 2007, the nova occurred. Located in the constellation Puppis, the nova is approximately 1,000 light-years from Earth. Despite not being seen at its peak immediately after detonation, the nova, now officially designated V598 Puppis, is one of the brightest observed during the past ten years.
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