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Tom Mazanec
2014-Oct-07, 10:33 PM
I am on a planet distant enough from a red giant/white dwarf binary to be habitable. At high noon local time, the white dwarf accretes the last gram of matter and supernovas. The dwarf was on the side of the giant facing the planet.
How long do I take to die? An hour? A minute? A second?

Grey
2014-Oct-07, 11:08 PM
I think that at that range, the neutrino burst (https://what-if.xkcd.com/73/) might be enough to kill you. If not, then definitely the radiation. Either way, that will arrive in light travel time. So by the time you become aware of it, you'll already be vaporized.

Jens
2014-Oct-07, 11:17 PM
I think there was an xkcd WhatIf episode about this. I think it said that at about that distance, the radiation from a supernova would be billions or something times as bright as a thermonuclear device exploding in contact with your eyeball.

Grey
2014-Oct-08, 02:02 AM
I think there was an xkcd WhatIf episode about this. I think it said that at about that distance, the radiation from a supernova would be billions or something times as bright as a thermonuclear device exploding in contact with your eyeball.Yes. I linked to it above. ;)

Ken G
2014-Oct-08, 10:11 AM
This might be a nitpick, but it is potentially important-- bear in mind that article is talking about a core-collapse supernova, which involves neutronization and that means one neutrino per proton in the star. A type Ia is a thermonuclear explosion, largely involving the fusion of carbon into iron. Iron has only a slightly higher ratio of neutrons to protons than carbon, so there will be less neutronization. However, it's only about a factor of 10 fewer neutrinos, so the conclusions are probably still valid.

Grey
2014-Oct-08, 01:01 PM
This might be a nitpick, but it is potentially important-- bear in mind that article is talking about a core-collapse supernova, which involves neutronization and that means one neutrino per proton in the star. A type Ia is a thermonuclear explosion, largely involving the fusion of carbon into iron. Iron has only a slightly higher ratio of neutrons to protons than carbon, so there will be less neutronization. However, it's only about a factor of 10 fewer neutrinos, so the conclusions are probably still valid.It is a nitpick, but that's okay. ;) That was one of the reasons (the other was the fact that I'm not sure exactly how far away the planet is in Tom's scenario; it doesn't matter much, so I didn't work it out) why I wasn't sure whether or not the neutrino burst would be lethal. I just thought it would be entertaining to point out the possibility, since dying from neutrinos is such an odd concept. But the initial burst of radiation will arrive at more or less the same time, and even though there's some variation in the amount of energy released by different types of supernova, they're all within a couple orders of magnitude or so, and that's more than enough to instantly vaporize any planet that's even vaguely nearby. Tom doesn't have any longer than light travel time from the star to live. My recommendation is that if you find yourself on a planet near a white dwarf that's accreting gas from a nearby red giant, it's time to move to a new neighborhood right away. By the time you get word that the supernova has started, it's already too late. :)

Ken G
2014-Oct-08, 01:05 PM
Yes, I agree that it is quite an interesting fate to be incinerated by neutrinos. If you have to go somehow...

George
2014-Oct-08, 01:17 PM
I wonder if the x-rays and positrons(?) from disk accretion would have been a serious problem prior to annihilation?

Ken G
2014-Oct-09, 08:13 PM
Yes, you are talking about something called a "microquasar" and they might be pretty nasty up close and personal.