Monday, June 07, 2010

Betelgeuse, Betelgeuse, Betelgeuse!

No, not the movie. The star.

Betelgeuse is a star not too far away from us, astronomically speaking. (600 light years) It's also frickin' huge, compared to our own Sun (In size, about 1000 times our Sun). Soon, it's going to explode in a massive, awesome supernova.

When a star is about to go supernova, it starts shrinking rapidly, as its core processes can no longer counteract the force of gravity. Betelgeuse has shrunk about 15% in the last 15 years. That's very fast. It could go boom any time now.

Got your attention yet?

Several different emails and forum posts around the internet have been to this extent. Unfortunately, the rumours of Betelgeuse's impending death is most likely greatly exaggerated.

Some background: Betelgeuse is a young star, only about 8.5 million years old. Large stars have much shorter lives than smaller stars, as they burn their fuel much faster, because they have much greater gravity to speed it up. Compare this to our own Sun which is about 5 billion years old, and estimated to be able to live for another 5 billion before it dies.

A star burns by fusing one fuel into another. Most of their lifetime is spent fusing hydrogen into helium. Our own Sun is at that stage still, and will be for another couple billion years. Once hydrogen runs out, it starts fusing the helium into carbon and then nitrogen and oxygen and neon and so basically continuing up the periodic table until it hits iron. Each of these reactions go faster and faster, and the time spent on say, neon, can be only a couple of thousand years compared to the millions or billions of years spent on hydrogen. Once it reaches iron it is no longer able to fuse that to a heavier element, gravity overwhelms the nuclear processes and contracts it really tight together... at which point the nuclear processes kick in one final time and explode in what is known as a supernova. The star ceases to be and becomes an ex-star.



(Table from Wikipedia)


Betelgeuse is approximately 20 solar masses, just as this table uses in its example. And it appears to have started fusing Helium into Carbon. It could go on for a while or it could complete really really quickly.

Betelgeuse is fairly far along in its cycle. It is going to explode "soon". BUT, this is "soon" on an astronomical scale. Those who say Betelgeuse is going to go supernova this summer, they're underestimating astronomical timescales a bit. Expert money says it's going to go within the next 5-10,000 years. Of course it could happen within our lifetimes, but it's very unlikely. Astronomically so. Unfortunately.

The distance keeps us safe. For a supernova to be actually dangerous to Earth or its inhabitants, it'd have to be within 25 light years approximately. Betelgeuse is 600ish. Way outside of what is dangerous.

Whatever Betelgeuse can fling at us will totally be dwarfed compared to what the Sun already does. The main force of the explosion will not be aimed at us (Angular momentum says that most of it will be ejected through the poles) but even if it were we'd not notice it because it's so far away and by that time it'll be too little to notice.

When it finally goes it will be spectacular, though. It will be visible in daylight. It'll be as bright as a full moon on the night sky. (It'll still only be pinhead-sized, so you won't see two suns or anything funky like that) It'll last for a couple of weeks before Orion suddenly loses his shoulder.


A lot of telescopes are being pointed at Betelgeuse these days, and you can be sure that if something really happens, you'll notice it. I wouldn't clear my schedule for it though.

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