Has Eta Carinae supernova already happened?

Stan Beer
Tuesday, 08 May 2007 17:43

Science - Space

The scientific world is still in awe after witnessing the most powerful explosion in human history as a gigantic star went supernova far away in another galaxy. However, it's a sobering thought to know that the same thing may have already happened to a comparitively nearby neighbour in our galaxy but the news just hasn't reached us yet.

The supernova with the scientifically clinical name SN 2006gy went off with a bang about 240 million years ago in an explosion that dwarfed all known supernovae in recorded history. The star that spawned such an enormous explosion was estimated to be approximately 150 times as massive as our sun - about as big as a star can get. In fact stars of such gargantuan proportions are thought to be intrinsically unstable with a relatively short life span of about 1 million years or so.

Unlike more common supernovae, which are not quite so massive and collapse under their gravity into black holes after they exhaust their nuclear fuel, the more massive SG 2006gy is thought to have exploded and spewed matter out into space with such violence, intensity and brightness that 240 million years later we are witnessing it here on Earth.

The science behind the explosion of SG 2006gy is a matter of conjecture for physicists. However, back in the real world, both scientists and lay persons are now looking towards a massive star called Eta Carinae in our own galaxy, the Milky Way.

Eta Carinae, a comparitive near neighbour just 7500 light years away, is thought to be of a similar size to the star that spawned SN 2006gy. What's more, Eta Carinae has already demonstrated itself in recent history to be a highly unstable and volatile beast.

Discovered by Edmund Halley in 1677, Eta Carinae, visible in the Southern Hemisphere, has brightened, subsided and brightened again by many orders of magnitude over the past three centuries. In the 1840s, it was one of the brightest stars in the sky and, after a period of subsiding, it brightened again during the late 1990s and can currently be seen with the naked eye.

The question that scientists are now asking is whether Eta Carinae is about to erupt in a massive supernova explosion like SN 2006gy. Or rather, did it happen around 7500 years ago, prior to the time of the ancient Egyptians? If so, we'll know pretty soon when the light from the event finally reaches us.

"We don't know for sure if Eta Carinae will explode soon, but we had better keep a close eye on it just in case," said Mario Livio of the Space Telescope Science Institute in Baltimore. "Eta Carinae's explosion could be the best star-show in the history of modern civilization."

What does "best star-show in history" mean exactly? Well, according to some astronomers, if the recently observed explosion of the star that resulted in supernova SN 2006gy has occurred with Eta Carinae just 7500 light years away, then life on Earth should not be affected - that's good to know. However, those of us who live the Southern Hemisphere, will be able to read books at night by Eta Carinae's starlight! At least we'll be able to save on electricity bills.