Will Eta Carinae Kill Us All?

I've seen a few posts on various websites regarding Eta Carinae and the possibility that it might wipe us out with a GRB. I won't give any of those posts credence by linking to them, but I would like to address some of the things they're saying...

What is Eta Carinae?

Eta Carinae is a star, or rather a system of stars, in the Carina constellation. It is located within our galaxy, in the region of 8,000 light years away. One of the stars (there are at least two) is of a type known as Luminous Blue Variable (LBV). It's big. Over the course of its life so far it has lost about thirty times as much mass as our Sun contains altogether, and still contains over a hundred times as much.

Given its mass and its age (about three million years), it is expected to go supernova fairly soon*. It might even go hypernova, which is a lot like going supernova, but even more over-the-top. Eta Carinae is a good candidate for producing a Gamma Ray Burst as it dies.

What is a Gamma Ray Burst, and why are they bad?

It's not a progressive rock band from the 1980s**. Essentially it's a burst, right, of gamma rays. If you'd like to know more, check out this post, but for the purposes of today's post it's enough to say that they're bad news.

GRBs are bad news for life for two reasons:

  1. On the side of a planet facing the burst, any organisms, from the smallest bacteria to dirty great humans, would be lucky to survive.
  2. I said they'd be lucky to survive, but that's relative: the burst would severely deplete the Earth's ozone layer, leaving surviving creatures wide open to fatal levels of ultraviolet radiation from the Sun.

Is Eta Carinae close enough to be a danger?

The general consensus is that any GRB going off within our galaxy would be close enough to cause us serious problems. And by serious, I mean extinction.

Will Eta Carinae kill us all?

If Eta Carinae went off tomorrow*** we'd probably be o.k. The thing is, with a supernova, even a hypernova, you get a massive explosion that's utterly bad news for anything closer than a given distance from it. This distance is, in astronomical terms, relatively close: we wouldn't suffer anything from the nova itself, and may not even see much of a light show from here.

The dangerous bit is the GRB itself. Unlike the vaguely spherical explosion of a nova that sends destruction out in all directions relatively close by, a GRB is more like a rifle shot, or maybe a shotgun blast that comes out of the poles as it explodes and sends nastiness much, much further. This is good news for us: it's only a problem if we're looking down the barrel of the gun, and much of the evidence indicates that we're not. I've found various values for the estimated angle of Eta Carinae's rotation. They don't all agree exactly, but they are all between 40 and 60 degrees away from our line-of-sight.

So now you can rest easy. Or you could give this post a look over.

* Remember that 'fairly soon' in astronomical terms could span thousands of years.
** I think that signifies a lost opportunity for the decade that brought us Hair Rock.
*** Or, rather, 8,000 years ago tomorrow in order for its effects to reach far enough by tomorrow.


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