Does anyone know how close a super nova can occur without radiating and killing most life on earth?

Specifically Betelegeuse is ~520 light years away and will go super nova within 3 million years. 520 light years is probably far enough away that earth would be safe, but its not that far cosmically speaking.

Anything within 50 light-years would most likely be fatal to all life on Earth

The question's been talked about on a number of different websites. The last time I looked the answer seemed to be about 25 light-years. Anything closer exterminates all life on Earth. Of course, in order to make the calculations, you have to make assumptions. The values you plug into your assumptions greatly affect your final answer. The best advice would be to stand back and wear lots of sun-block.

Does anyone know how close a super nova can occur without radiating and killing most life on earth?

Specifically Betelegeuse is ~520 light years away and will go super nova within 3 million years. 520 light years is probably far enough away that earth would be safe, but its not that far cosmically speaking.

How would you look at our own galaxy's central supermassive black hole going nova? How about two supermassive black holes? Welcome the Andromeda galaxy. See it live in about 5 billion years from now when these two merge.

I don't think black holes can go nova...

They can and they do. A supernova is a black hole while it is consuming gas and other matter. It superheats the gas around it, it (the gas) rotates close to the speed of light and two jets of superheated gas shoot from it (the black hole).
If a dormant black hole gets close to a new source of gas and caputures the gas clouds (or a star) by its' gravity, then it again becomes an active nova.

Really?

I looked around and didn't see anything that related them to black holes at all... you'd think they'd mention that...

I got this off the hubble site
A supernova is the explosive death of a star, which unleashes a burst of light through the cosmos. Supernovas happen in two different ways:

* When massive stars run out of fresh nuclear fuel, there is no more pressure to sustain them against their own weight. The central part of such a star then collapses. The outer layers of the star fall in on the core and then rebound in a tremendous explosion.
* Matter piling up on the compressed core of an already-dead star can reach sufficient density to trigger a thermonuclear explosion.



I also read most of this article and it didn't say anything about black holes...
http://www.aavso.org/vstar/vsots/0301.shtml


Are you sure that blackholes can nova? If so, do you have a link so that I can learn a bit more about this? :)


Edit:

found this at nasa...
http://imagine.gsfc.nasa.gov/Images/basic/xray/supernova_cycle.gif

...

Now that I think of it...
:D I'm very terribly and deeply sorry. I confused it with a quazar (sp).
The effect is simmilar though.
But a black hole can be created when a star goes nova.

no worries, I'm not an expert or anything... so I was really was curious if I was wrong or not...

i heard of something called a hypernova, supposed to be many times more powerful than a supernova, it was originally on armageddon.com, but taken off when the site was remodeled. maybe cause it was bogus, i don't know. any idea what it is?

http://www.astrobio.net/news/article420.html

I once calculated for a university exercise that if Alpha Centauri A, only 4.3 light years away, were to somehow become a supernova (clearly impossible for a star of that mass), it would still have an apparent magnitude about 3 points less than the Sun as seen from Earth - assuming it was an isotropic explosion, and not collimated into a narrow jet pointed straight at us! Its heat and radiation wouldn't be overpowering... the real threat would be from the intensely radioactive debris cloud, which would engulf our solar system 2 or 3 decades later.

Really? That is interesting! Of course the debris cloud is also subject to the inverse square law, so would quickly also become reasonably safe- perhaps by 10 ly or so...

here is an interesting study of the effects of nearby supernovae, by the way.
http://stupendous.rit.edu/richmond/answers/snrisks.txt

Remember as well there are several different types of supernovae, some brighter than others.

Since it would be hotter than the Sun, it should be more energetic in gamma rays than in visible light. That could be a problem.

Remember as well there are several different types of supernovae, some brighter than others.

Yes - the worst would be type 1a, right? A white dwarf being completely shattered - no further collapse, to neutron star, just all that enormous electron degeneracy pressure converted into radiant energy...

Although this is normally triggered by excessive accretion of mass from a companion star (if the word normal can be applied at all to supernovae), might it not also happen if 2 white dwarfs collide and merge? If they're both fairly massive to start with, their combined mass could be greater than Chandresekar's limit.

Collisions between hyperdense objects are always bad news; however they seem to be rare events.
Neutron stars and black holes give off much more energy than ordinary supernovae when they collide, this is one mechanism for a particular type of gamma ray burst. White dwarfs are very small targets, but their collisions would be somewhat less cataclysmic.

White dwarfs are still much bigger than neutron stars, or black holes of stellar mass - plus there are almost certainly more of them, so they must be more likely to collide.

I wonder just how many white dwarfs there will be, in a galaxy the size of ours, after all normal star formation and evolution has run its course (about 100 trillion years from now)? By then, even the vast hordes of long-lived red dwarf stars will have cooled and shrunk into low-mass white dwarfs - which are the least dense, and therefore, paradoxically, the largest. With a long span of future star formation adding to the galactic population of today, perhaps there will be enough white dwarfs (and brown dwarfs) available to make collisions a relatively common occurence?

If the white dwarfs exist as binaries in a common atmosphere then there's a mechanism to make them merge. The friction of their passage thought the atmosphere would steal orbital energy, making them spiral into each other. You do not have to have much of an atmosphere if you're willing to wait billions of years for the event.

A "common atmosphere" would indicate a symbiotic binary - close enough to exchange mass, which is exactly how normal novae come about when one star becomes a white dwarf first.

However, by the time both components have reached this point in their life cycles, the system as a whole will have lost a lot of mass in the respective asymptotic giant phases and subsequent planetary nebulae. If one star flared up as a nova while the other was transferring mass to it, this explosion would drive even more gas away from the system. With only the 2 small, compact remnants left, there would probably be insufficient diffuse material around either star to form a significant mutual atmosphere.

Of course, their orbits could still decay eventually through chance close encounters with other stars, and ultimately by gravitational radiation...

Well if Betelegeuse it would certainly create a nice view. Apparently it would be as bright as the moon.

Is the 3 million years just an estimate? What if it exploded tommorrow, or 50 years ago? We could see the light pretty soon.

For all we know, it COULD explode tomorrow... the hugely distended outer layers of a supergiant like Betelgeuse make terminal collapse of the core impossible to observe, and we can't analyse the neutrino flux from a distant star. It's unlikely, of course - but there's so much we don't yet know about stellar physics, and we've yet to observe a supergiant becoming a supernova until after the detonation.

Huge 'star-quake' rocks Milky Way

Astronomers say they have been stunned by the amount of energy released in a star explosion on the far side of our galaxy, 50,000 light-years away.

The flash of radiation on 27 December was so powerful that it bounced off the Moon and lit up the Earth's atmosphere. The blast occurred on the surface of an exotic kind of star - a super-magnetic neutron star called SGR 1806-20.

If the explosion had been just 10 light-years away, Earth could have suffered a mass extinction, it is said.
read more -> http://news.bbc.co.uk/1/hi/sci/tech/4278005.stm

http://news.bbc.co.uk/1/hi/sci/tech/4278005.stm
One calculation has the giant flare on SGR 1806-20 unleashing about 10,000 trillion trillion trillion watts. . . We have observed an object . . . releasing more energy in a 10th of a second than the Sun emits in 100,000 yearsThese numbers are cumbersome; saying that it releases as much energy in one second as the sun does in 1,000,000 years would be the same figure.

The Sun's output is 400 x 10<Sup>24</Sup> watts. Since there are 30 x 10<Sup>6</Sup> seconds in a year, in a million years there are 30 x 10<Sup>12</Sup> seconds. It is as bright as 30 trillion suns. Wear lots of sun block.