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Supernova smothered
by own dust

Posted: 13 October 2010

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A 50 solar mass star ending its life in a supernova event is obscured by its own dust cloud, the first of its kind ever viewed by astronomers.

The serendipitous observation was made as part of the Spitzer Space Telescope Deep Wide Field Survey, which was focused on seeking out hot spots that would give away the locations of active galactic nuclei (AGN), galaxies with supermassive black holes at their centres.

In this artist's impression, a vast shell of dust and gas obscures the supernova event. Image: NASA/JPL-Caltech/R. Hurt.

Supernovae release most of their energy as light rather than heat, and one hotspot in the Spitzer data stood out above the rest. Located in a galaxy three billion light-years from Earth, the signal was not typical of an AGN, an observation that was confirmed by visible light spectra obtained using the ground-based Keck telescope in Hawaii.

“Over six months, it released more energy that our Sun could produce in its entire lifetime,” says SzymonKozlowski. The heat blazed from the object for around six months before fading away in March 2008, typical behaviour of a powerful supernova explosion. Its temperature was measured as around 700 degrees Celsius, leading the astronomers to conclude that dust was the culprit in absorbing the supernova's light energy and dissipating it as heat.

Estimated as at least 50 times as massive as the Sun, the star underwent two periods of ejection, one 300 years ago and one just four years ago, with dust and gas from both explosions hanging closely around the star. “We think the outer shell must be nearly opaque, so it absorbed any light energy that made it through the inner shell and converted it to heat,” says Christopher Kochanek of Ohio State University.

While this is the first observation of a star choking on its own dust, astronomers think that events like these were much more common in the early Universe. “These events are much more likely to happen in a small, low metallicity galaxy,” he says. That is, in young galaxies that are made up of predominantly hydrogen and helium, and no heavier elements.

This star's story is far from over, however. The team predict that if astronomers turn their telescopes back to this object in a decade they may observe brightening as the shockwave from the exploding star reaches the inner dust shell and slams it into the outer shell.