How would a close supernova effect us?

No, not the sun… that’s TOO close!

Most supernovae that we’ve seen have been extra-galactic, and so have no real effect on us. Even the 1604 supernova, which was within the Milky Way, was 20000 LY away, and didn’t affect us other than our visualization of the sky.

But what would happen if a closer star went nova? For example, what if Ross 128 (10.87 LY away) went nova back in 1993 and the light/energy from the nova starts reaching us now? If Ross 128’s mass is too small to nova, then simply insert any other “local” star. Would we be in any danger? What effects would it have on us (other than a bright new light in the sky)? If solar matter is expelled (which would be travelling slower than the energy), would it be a danger to us when/if it reached us and how long would it take to get here?

Zev Steinhardt

I don’t have an online cite, but taken from “The Science of Discworld”:

The radiation from a sun going nova within about 20 light-years from us would kill all higher lifeforms on the planet. A gamma ray burst within about 100 light-years from us would do the same. Some bacteria, especially those protected deep in the ocean or deep in the Earth’s crust would probably survive.

Luckily, the odds of either of these things happening within our lifetimes are vanishingly small.

Does anyone have any figures on the number of stars within 20 & 100 light-years of us? Am I right in thinking stars always become red-giants before they go nova, or does that only apply to stars on the main sequence? Are there any red-giants within 20 light years?

The Bad Astronomer has a nice little article on the Danger from nearby supernovae.

Some astronomers believe that a gamma ray burst type of supernova could sterillize an entire galaxy. Or at least on the order of thousands of light-years around.

Likely not an entire galaxy:
W49B: Smoking Gun Found for Gamma-Ray Burst in Milky Way
The W49B remnant is only ~35,000 light years from earth.
Sadly, none of the articles I found on W49B gave a date for the hypernova, however supernova remnants are typically visible for at most a few hundred thousand years.

Well, according to PBS’s documentary “Death Stars” and the associated website, a close-by gamma ray burst could cause us all to die horribly of cancer, radiation poisoning, or starvation. This isn’t necessarily caused by supernovae, but it seems relevant here - it might give an idea of the sort of damage a supernova might do. shrugs

It’s not an exact science. Some calculations indicate a supernova would have to be as close as 20 light years away to be a problem; others say a supernova as far as a 1000 light years away might be a problem. Obviously how one defines a “problem” is one factor.

Unfortunately, we may get a chance to gather evidence of this phenomena. Betelgeuse, a star approximately 500 light years from Earth, could turn into a supernova. This would by far be the closest any supernova has ever occurred. (The closest actual one was approximately 20000 light years away.)

So the situation is that we probably won’t have a supernova near Earth and if we did it probably wouldn’t be close enough to kill us.

To be a bit more exact, Betelgeuse is 427 (+/-75) ly away and is the closest supernova candidate. The next closest is probably Antares at 604 (+/-134) ly.

The Crab Nebula is a remnant of a supernova that was seen in 1054 by Chinese astronomers. It’s 6300 ly away and is the closest supernova recorded in history. However, there’ve only been 5 supernovae in our galaxy recorded in history, so that’s not a big sampling.

The closest supernova remnant currently visible seems to be the Vela SNR at about 815 ly. It’s age is about 11,000 years.

How LONG a duration would the blast of X-rays from a supernovae be? If short enough, only the side of the planet facing the star would be devastated. Coould this happen?

Actually, we had a thread in which the effects of Betelgeuse going kablooey were extensively discussed, but I can’t for the life of me find it. The general consensus was that astronomy would be a lot more difficult for a few months, because the magnitude of the supernova would be brighter than the moon, but that the X-ray problem wouldn’t be that bad. But I’m just repeating this from memory.

Might this be the earlier thread you mean?
An astronomy question: regarding Betelgeuse going supernova

Well if we say that a Type II supernova emits 10[sup]10[/sup]times the current solar flux (3.9x10[sup]26[/sup]W) initially and it slowly dies away over 150 days to 10[sup]8[/sup] then the amount of energy hitting earth on day 0 would be as follows

Lightyears	W/m^2
5	        1375.52
10	         343.88
15	         152.84
20	          85.97

Currently the Earth receives about 1300 W/m[sup]2[/sup] daily so we would be looking at a fair bit of energy initially but I’m not sure that it would be catastrophic.

I’d be more worried about the heavy ions showing up years after we see the thing.

The gamma rays themselves wouldn’t. The gamma rays only last for seconds at most, so as ralf124c points out, only half the planet would be sterilized. However, at least some gamma ray bursters seem to be caused by high-energy supernovae, so you’d still get all the same problems as with a supernova.

For those who would like to enjoy the speculations of a Ph.D. astronomer on this topic, Charles Sheffield wrote a duology, Aftermath and Starfire, exploring the effects of a (very) nearby supernova. IMO, these are not among his best works, but still very readable science fiction. Sheffield knew how to get his readers involved (I really hate he died).