Perilous Supernovae?

General Questions
#1

There are a couple of types of stars that can become supernovae at the end of their life cycle, thus producing an astronomical event with an energy output “like a 10[sup]28[/sup] megaton bomb (i.e., a few octillion nuclear warheads)” according to Nasa at http://imagine.gsfc.nasa.gov/docs/science/know_l2/supernovae.html

I imagine the blast radius is pretty large.

My question is, how many stars that are currently capable of going supernova are close enough to Earth to affect us if they do?

Is this something I should add to my “Worry About This” list, along with meteors and chupacabras?

#2

Well, the closest star which is going to go any time soon is Betelgeuse, at approximately 800 light years-- We expect to see it go sometime in the next milennium (which, of course, means that it’s probably already exploded, and we just don’t know it yet). It’s unknown how much effect this would have on us, but at the very least, we’d get a lot of light from it: It should be brighter than the full moon, and with all that magnitude concentrated into a point source in the sky, it’d probably be painful to look at directly. X-ray and gamma radiation probably wouldn’t be too severe, but the shockwave might cause problems (yes, in space, you really can hear screams, if they’re loud enough, like a dying star. No vacuum is perfect). Don’t worry too much, though, because the shockwave will travel at considerably less than light speed, so we’ll have plenty of advance warning to figure out something to do about it.

If you really want to worry about death from above, think gamma ray bursters, not supernovae. One going off close enough to Earth would be quite sufficient to sterilize everything in sight, and we probably wouldn’t be able to see the progenitor of a burster very far in advance, so there just might be one close enough that we don’t know about. On the other hand, gamma ray bursts are very short-lived, lasting a few seconds at most, so it’d only sterilize the half of the planet which happened to be facing in that direction.

#3

Actually, we have no idea when Betelgeuse will let go. It might do it tonight, or it might wait 10,000 years, or more. These things are nearly impossible to judge.

Another star that IMO is more likely to go sooner than Betelgeuse is Sher 25. It’s pretty far (20,000 light years), so not likely to do much to us. It looks a lot like the star that blew up in 1987 in the southern hemisphere skies. It’s actually somewhat more massive, and so its lifetime is shorter. It almost certainly has less than 10,000 years left to it. When it does go it’ll be bright, but probably not overwhelmingly so. It’s a blue supergiant, meaning it is dense, and the explosion loses a lot of energy fighting its way out of the star’s outer layers. That’s the same reason why the one in 1987 was not nearly as bright as people thought it would get.

Check this out for more, and see a Hubble image too:

Michael Richmond is a supernova researcher and has a great page about dangers from nearby SNe:

http://www.tass-survey.org/richmond/answers/snrisks.txt

That will answer most of your questions!

#4

Then there’s Eta Carinae, a variable star 7,500 light years away which could go kaplooey any time now.

http://www.space.com/scienceastronomy/astronomy/milan_eta_carinae_000307.html

(my first attempt at posting a link, so I’m sorry if it doesn’t work)

#5

Id check the spectral analysis of any star you have concerns about.
Each element absorbs (and emits ) only certain electromagnetic frequencies.
Fusion is the apparatus by which stars are powered, and the furst fuel used is hydrogen. When the hydrogen is used up, its byproducts-helium, begin to fuse. Fusion of fuel byproducts continue up to iron. Apparently, iron has the most stable atomic nuclei, and no heavier element can support fusion, and soon thermonuclear catastrophe results.
If iron shows up in a star’s spectrum, start packing.

#6

While that’s true, you only see the stuff that’s at the surface of the star. The fusion occurs deep in the core of the star, so you never see the reaction endproducts until they scream out at 15% the speed of light. :wink:

The Sun has iron in its spectrum! As I said, the stuff that happens near the core stays near the core; there isn’t enough time for it to get to the surface before the star blows. In this way, you can’t tell when a star is going to explode.

As far as Sher 25 goes, we know from its spectrum that it is a hot blue supergiant, and we do have one example (supernova 1987A) of this type of star exploding. We also see gas around it in an extremely similar configuration as that around 87A, so we are pretty sure these two stars are moving along the same lines.

Eta Carina is another good possibility. No one understands this star; we don’t even know if it’s a binary! The evidence points that way, but there is no confirming detection of a second star. But it will blow one day, and that should make for quite a show. There is a lot of junk around it, which will light up very effectively when flooded with 10^50 ultraviolet photons!