# Neutrinos in Supernova Remnants

Mentor

## Main Question or Discussion Point

In How A Supernova Explodes, Scientific American, by Bethe and Brown, there is this passage.

Bethe and Brown said:
Even if the compact remnant ultimately degrades into a black hole, it begins as a hot neutron star. The central temperature immediately after the explosion is roughly 100 billion degrees Kelvin, which generates enough thermal pressure to support the star even if it is larger than 1.8 solar masses. The hot nuclear matter cools by emission of neutrinos. The energy they carry off is more than 100 times more than the energy emitted in the explosion itself; some 3*10$^{53}$ ergs. It is 10% of the mass equivalent of the neutron star.
Wow 10% of the mass equivalent of the neutron star. What an amazing number. But as I see it, the number of neutrinos should equal the number of protons in the pre collapse core material (which should be roughly the same as the number of electrons and the number of neutrons). So an electron and a proton combine, yielding a neutron and a neutrino. In addition those parent particles have lots of kinetic energy at 100 billion degrees.

But the neutrino is exceedingly light. 10% of the neutron star's mass equivalent seems like far more energy than these neutrinos can carry away. I must be missing an important factor, either in number of neutrinos or in the energy per neutrino.

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SteamKing
Staff Emeritus
Homework Helper
There are even more neutrinos produced during the core collapse leading to the formation of the supernova itself.

It's how the iron nuclei in the core are split apart and converted into neutrons, which form the nascent neutron star, generating a shower of neutrinos in the process. If conditions are favorable, a handful of these neutrinos might be observed here on earth eventually.

http://en.wikipedia.org/wiki/Type_II_supernova

Chronos
Gold Member
Neutrino emission is believed to be the principle transport mechanism for binding energy in a core collapse event. The core, which is comprised of heavy elements with high binding energies, is the principal source of SNII neutrinos. The typical energy carried off per neutrino is in the range of 10-30 Mev. This is much greater than the typical p-p energy carried off by a typical photon in a typical main sequence star - which is about 0.3 Mev. The rate of p-p reactions in the core of a type II supernova is also astronomical [pardon the pun] compared to a typical MS star. The end result is an enormous number of enormously energetic neutrinos escaping from the core.

Drakkith
Staff Emeritus
How exactly does the hot core create and emit neutrinos from this super-high temperature? What reactions are taking place?

Drakkith
Staff Emeritus
See http://www.jinaweb.org/docs/nuggets_07/frohlich_nup-process.pdf, The Neutrino p-Process, for discussion.
Hmmm... that appears to explain how anti-neutrinos lead to the formation of free neutrons by combining with free protons. I'm asking about how the neutrinos are emitted inside the neutron star. Are these neutrinos created only when the protons combine with electrons to form neutrons during the collapse, or are they also created by some other mechanism after the neutron star forms but is still extremely hot?

Chronos
Gold Member
Neutrinos are routinely produced by all stars, but, emission rates during core collapse events are exponentially enhanced. Proton rich elements in the core are deconstructed and reconstructed at a furious pace producing phenomenal energy. This energy is conveyed throughout the star resulting in more emissions. After these fireworks subside, the resulting neutron star continuous production of neutrinos, but, at a more relaxed pace and via various other mechanisms. See http://cds.cern.ch/record/479566/files/0012122.pdf, Neutrino Emissions from Neutron Stars, for discussion.

In How A Supernova Explodes, Scientific American, by Bethe and Brown, there is this passage.

Wow 10% of the mass equivalent of the neutron star. What an amazing number. But as I see it, the number of neutrinos should equal the number of protons in the pre collapse core material (which should be roughly the same as the number of electrons and the number of neutrons). So an electron and a proton combine, yielding a neutron and a neutrino. In addition those parent particles have lots of kinetic energy at 100 billion degrees.

But the neutrino is exceedingly light. 10% of the neutron star's mass equivalent seems like far more energy than these neutrinos can carry away. I must be missing an important factor, either in number of neutrinos or in the energy per neutrino.
umm the nneutrino is it faster than light or is the Tachyon also faster than light in the special theory of relativity

well this theory is yet to be prven that is the Tachyon travelling faster than the speed of light

Matterwave
Gold Member
umm the nneutrino is it faster than light or is the Tachyon also faster than light in the special theory of relativity
Nobody said the neutrino goes faster than light. The OP was talking about the energy emitted by neutrino emissions is more than that emitted by photon emissions. This has nothing to do with the speed of neutrinos or photons.

Neutrinos travel very close to light speed, but there are no experiments showing they travel faster than light.

Drakkith
Staff Emeritus