"Another one lights the dust"

Ohio State astronomers were searching the skies for black holes. Instead, they discovered a giant star whose death was hidden in a cloud of dust.

While many such odd supernovae have probably occurred before, this is the first time astronomers have ever witnessed it.

Over six months, the distant star flared with more energy than our sun could produce in its entire lifetime. It must have released a tremendous amount of light, the astronomers determined--and most of it was captured by the dust, which heated to 700°C (almost 1,300°F). That's hotter than the surface of Venus, the hottest planet in our solar system.

In a paper published online in the Astrophysical Journal, Christopher Kochanek, Ohio Eminent Scholar in Observational Cosmology, and his colleagues describe how the supernova appeared in late August 2007, as part of the Spitzer Space Telescope Deep Wide Field Survey.

The astronomers were scanning the survey data for active galactic nuclei (AGN), super-massive black holes at the centers of galaxies. AGN radiate enormous amounts of heat as material is sucked into the black hole. In particular, the astronomers were searching for hot spots that varied in temperature, since these could provide evidence of changes in how the material was falling into the black hole.

Normally, astronomers wouldn't expect to find a supernova this way, explained then-Ohio State postdoctoral researcher Szymon Kozlowski. Supernovae release most of their energy as light, not heat.

But when the dust absorbed the light from this particular supernova in a galaxy some 3 billion light years from Earth, it created a hot spot that stood out in the Spitzer data.

Because of the alignment of the galaxy with Earth and our sun, astronomers were not able to see what the event looked like to the naked eye while it was happening. But Kochanek believes that we might see the star brighten a decade or so from now. That's how long it will take for the shockwave from the exploding star to reach the inner dust shell and slam it into the outer shell. Then we'll have something to see here on Earth.

We do have at least one chance to see a similar light show closer to home, though.

"If Eta Carinae went supernova right now, this is what it would probably look like," Kochanek said, referring to the brightest star system in our Milky Way Galaxy.

The two stars that make up Eta Carinae are 7,500 light years away, and they host a distinctive dust shell dubbed the Homunculus Nebula, among other layers of dust. Astronomers believe that the nebula was created when the larger of the two stars underwent a massive eruption around 1840, and that future eruptions are likely.