Bad Astronomy

M82 stifles a cosmic belch

M82 is a weird galaxy. Deep images of it show vast amounts of gas obviously screaming out from it, as if the galaxy itself is exploding. For a long time it was thought that exploding stars were driving the gas out of the galaxy, but now we know that M82 is a starburst galaxy, where huge numbers of stars are being born. There are so many young, hot, massive stars being made that their fierce stellar winds are driving out the material seen.

But those kinds of stars are exactly the types that live short furious lives, dying after only a few million years in titanic supernovae explosions. And now, astronomers are reporting that one has been seen… but the thing is, it can’t be seen.

Uh, say what?

SN 2008iz in M82
SN2008iz in M82. Embiggen by clicking.

OK, here’s the deal. Newly formed stars produce a lot of dust, complex molecules that are really good at absorbing visible light. M82 is lousy with new stars, so it’s choked with that dust, which blocks the visible light coming from the galaxy’s heart. However, infrared and radio light can go right through the dust. So the newly discovered supernova was seen using radio telescopes; it’s completely invisible in visible light. M82 is close, only 12 million light years away; if it weren’t for all that dust the supernova would have been visible in binoculars!

The supernova, called SN2008iz, was only just discovered. It was seen in some older data from last year, but is not seen in data taken before then. The size of the object – 20 light days, about 500 billion km, or very roughly 50 times the size of our solar system – is pretty good evidence of it being the expanding debris from an exploding star, and the circular shape is also pretty conclusive; that’s just what you expect from an expanding shell of gas.

By combining the power of several radio telescopes, astronomers can see this object in some detail, even though from our distance it looks very small. Better yet, as the debris grows larger we can watch it expand, giving information on the energy of the explosion and what sort of material surrounds it as well, just as we did for a supernova that happened in 1987.

Supernovae create the heavy elements in the Universe, including iron and calcium which are in our bones and blood. I think that’s enough to make them worthy of study all by itself… but they are also just so freakin’ cool. Unimaginably, impossibly violent explosions due to a star ending its life not with a whimper but with a bang that can outshine entire galaxies… and even that mighty light can be hidden, shrouded by the expulsions of stars just being born.

I’d say it’s ironic, but since iron is actually involved that seems somehow wrong. Still. It’s cool. And that’s ironic too.