For a scene in a SciFi book, I want to know: Is it possible to estimate how much energy per m² an object would receive that hides behind an in-system planet when the sun goes nova?

  • $\begingroup$ Your question diverges from the title into two separate ones, you might want to expand the question body to ask both related questions in appropriate order lest one not be answered due to subduement by the other. Also, have you managed to find any relevant information via research regarding your situation? If so, it would be wise to link them to give the community an idea of the effort put into this. $\endgroup$ – Grant Thomas Aug 23 '11 at 9:18
  • $\begingroup$ Neither Google, Alpha nor Wikipedia turned anything useful up (either a formula or estimates of the energy generated). I'm also not sure which processes take place; I'm aware that fusion can convert about 7% of the matter into pure energy (H -> Fe) but I have no idea how the pressure changes, shock waves, etc. change this picture. $\endgroup$ – Aaron Digulla Aug 23 '11 at 18:22
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    $\begingroup$ Even if the planet could shield you from the light, supernova release an awful lot of energy in neutrinos, and hiding behind a planet would be completely useless. Phil Plait's book Death from the Skies estimates that they would give you cancer out to about 30 light years, with large uncertainties. $\endgroup$ – EHN Aug 25 '11 at 12:11
  • $\begingroup$ Neutrinos don't interact much, so I'm wondering if the blast would have any effect at all. My bigger concern would be gamma and beta radiation. $\endgroup$ – Aaron Digulla Aug 29 '11 at 8:14
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    $\begingroup$ No, neutrinos don't interact much... this is why shielding is hopeless. SN produce so many, though, that the minimal interaction may be overwhelmed by sheer numbers. Yes, though, by guess is that other forms of radiation would be more immediate problems; neutrinos are just what I could find the most obviously applicable reference for, as the planet can just be ignored. $\endgroup$ – EHN Aug 29 '11 at 12:12

Is it possible to estimate? Yes. I'll give it a quick try. But the details of whether the planet will be incinerated and so on will make the reality much more complicated.

As a ballpark, I think supernovae release about $10^{53}$ erg of energy. Spread over a sphere of, say, 1 AU gives $3.55\times10^{22}$J.m$^{-2}$. This energy isn't all released in one go and I don't know how much is radiative or kinetic. If its released over, say, 20 days, that gives $2.06\times10^{16}$W.m$^{-2}$ For comparison, the Sun emits 1368 W.m$^{-2}$, or 15 trillion times less.

The timescale is roughly the time it takes for observed supernova luminosities to rise to a peak but much shorter timescales might be relevant. About 1% of that energy is released in a few seconds in a neutrino burst, but they don't interact much. Also, 1 AU is pretty arbitrary. A star that undergoes core-collapse must be bigger than the Sun, so its habitable zone would be much further away. 100 AU might be just as reasonable and reduce the energy flux by a factor of 100$^2$.

To estimate further, you could work out how much energy your planet would absorb based on its cross-section and compare that to its gravitational binding energy to get a rough guess about whether it would survive the blast. Hope this helps though.

  • $\begingroup$ Is that number, total energy, or energy not emitted as meutrinos, which I think are maybe 99% of the total energy. I recall some rations from decades ago for core collapse SN. About one part in a humdred went mostly to kinetic energy of the ejecta, and maybe one part into radiaoactive nuclei, whose decay keeps the ejecta lit up, i.e. it was supposedly the source of most of the emitted light. Of course the time scale of stars with eight or more solar masses are hundreds of times shorter than of the sun, so assuming life takes billions of years it doesn't have time to form. $\endgroup$ – Omega Centauri Aug 25 '11 at 19:16
  • $\begingroup$ I just took a look at Wikipedia, and I think I erred. They say $10^46$ J is in the neutrino burst, which is in line with my remembering from somewhere that the total energy is around 100 times that. I'll tweak my answer. Also, good point about larger stars evolving faster. $\endgroup$ – Warrick Aug 26 '11 at 7:11
  • $\begingroup$ I think it is that 99% disapears promptly as neutrinos, not 1%. $\endgroup$ – Rob Jeffries Apr 26 '16 at 21:23

Supernovae can release several times 10^44 J of energy. This has resulted in the adoption of the foe (10^44 J) as the standard unit of energy in the study of supernovae.

The Foe is a unit of energy equal to 10^44 joules. To measure the vast amounts of energy that produces a supernova, the scientists used a unit of energy occasionally called foe was an acronym for Fifty One Ergs or 10^51 ergs (erg in English). This unit of measurement was ideal for having the energy of these phenomena as a typical supernova emits about one foe of observable energy (visible light). By comparison the Sun throughout its entire life has given just 1.2 foe. Well, assuming constant luminosity throughout his life 3.827 × 10^26 W × 10^10 years ≈ 1.2 foe. (taken wikki)

i hope i serve you.

  • $\begingroup$ Please specify what sort of supernova your answer refers to. $\endgroup$ – Rob Jeffries Apr 26 '16 at 21:21

Talking to an astronomer, he came up with a good suggestion: Google for "supernova simulation". There are a couple on Youtube. And there are also many papers.


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