Initiating mechanism of supernovae

[ChrisVer]

I think that our current knowledge on the initiating mechanism of supernovae is that they happen due to neutrinos interacting with the inner layers of a star and then accelerating them away from the core.
I am having some trouble in understanding that idea. Of course this could be plausible if neutrinos interacted strongly with matter, but that's not the case... At least it's not the case for pushing away 80++ % of the star's mass...
Of course it doesn't have to be neutrinos at all (the inner layers will drift the outer ones etc). But I can't even understand how this can really happen...

Can someone please give a satisfactory explanation?

At first we would have to admit that the neutrino emission for some reason raises in extreme numbers (also I am not sure if this could overcome neutrinos' weakly interacting nature)...why would that happen to a dying star's core?

 

[SteamKing]

I don't know anything about neutrinos being responsible for initiating a supernova. The loss of the envelope of the star, as far as I know, is due to the shock waves created by the collapse of the stellar core once its nuclear fuel has been exhausted and fusion no longer occurs.

Do you have a reference for any articles which discuss this neutrino initiation theory?

 

[mfb]

Neutrinos are always produced at high speed, so neutrinos produced in the core that interact in the outer part will accelerate this a bit outwards - but it would surprise me if that is a significant effect in supernovae.

At first we would have to admit that the neutrino emission for some reason raises in extreme numbers (also I am not sure if this could overcome neutrinos' weakly interacting nature)...why would that happen to a dying star's core?

In the extremely hot and dense core, many nuclear reactions happen, so many unstable nuclei are produced and decay quickly afterwards.

 

[ChrisVer]

I had heard of the neutrino initiating mechanism at a seminar... For now I can quote something I found online (see attachment).

As for the whole, the neutrinos play the role of initiating mechanism (they don't move the whole procedure)- they somehow "push" the inner layers and so the everything is pushed. But for me still it's weird to think of weakly interacting particles to cause something so spectacular...

 

[Drakkith]

From wiki:http://en.wikipedia.org/wiki/Supernova

In lower mass cores the collapse is stopped and the newly formed neutron core has an initial temperature of about 100 billion kelvin, 6000 times the temperature of the sun's core.[72] 'Thermal' neutrinos form as neutrino-antineutrino pairs of all flavors, and total several times the number of electron-capture neutrinos.[73] About 1046 joules, approximately 10% of the star's rest mass, is converted into a ten-second burst of neutrinos which is the main output of the event.[71][74] The suddenly halted core collapse rebounds and produces a shock wave that stalls within milliseconds[75] in the outer core as energy is lost through the dissociation of heavy elements. A process that is not clearly understood is necessary to allow the outer layers of the core to reabsorb around 1044 joules[76] (1 foe) from the neutrino pulse, producing the visible explosion,[77] although there are also other theories on how to power the explosion.[71]

Reference number 75: http://adsabs.harvard.edu/doi/10.1086/169405

 

[SteamKing]

This article is only partially quoted, so I can't say that a neutrino initiating mechanism is discussed.

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

has the following description of the events surrounding core collapse:

When the core's mass exceeds the Chandrasekhar limit of about 1.4 solar masses, degeneracy pressure can no longer support it, and catastrophic collapse ensues.[9] The outer part of the core reaches velocities of up to 70,000 km/s (23% of the speed of light) as it collapses toward the center of the star.[10] The rapidly shrinking core heats up, producing high-energy gamma rays that decompose iron nuclei into helium nuclei and free neutrons via photodisintegration. As the core's density increases, it becomes energetically favorable for electrons and protons to merge via inverse beta decay, producing neutrons and elementary particles called neutrinos. Because neutrinos rarely interact with normal matter, they can escape from the core, carrying away energy and further accelerating the collapse, which proceeds over a timescale of milliseconds. As the core detaches from the outer layers of the star, some of these neutrinos are absorbed by the star's outer layers, beginning the supernova explosion.

For Type II supernovae, the collapse is eventually halted by short-range repulsive neutron-neutron interactions, mediated by the strong force, as well as by degeneracy pressure of neutrons, at a density comparable to that of an atomic nucleus. Once collapse stops, the infalling matter rebounds, producing a shock wave that propagates outward. The energy from this shock dissociates heavy elements within the core. This reduces the energy of the shock, which can stall the explosion within the outer core.[12]

The core collapse phase is so dense and energetic that only neutrinos are able to escape. As the protons and electrons combine to form neutrons by means of electron capture, an electron neutrino is produced. In a typical Type II supernova, the newly formed neutron core has an initial temperature of about 100 billion kelvin, 10$^{4}$ times the temperature of the sun's core. Much of this thermal energy must be shed for a stable neutron star to form, otherwise the neutrons would "boil away". This is accomplished by a further release of neutrinos.[13] These 'thermal' neutrinos form as neutrino-antineutrino pairs of all flavors, and total several times the number of electron-capture neutrinos.[14] The two neutrino production mechanisms convert the gravitational potential energy of the collapse into a ten second neutrino burst, releasing about 10$^{46}$ joules (100 foes).[15]

Through a process that is not clearly understood, about 10$^{44}$ joules (1 foe) is reabsorbed by the stalled shock, producing an explosion.[a][12] The neutrinos generated by a supernova were actually observed in the case of Supernova 1987A, leading astronomers to conclude that the core collapse picture is basically correct. The water-based Kamiokande II and IMB instruments detected antineutrinos of thermal origin,[13] while the gallium-71-based Baksan instrument detected neutrinos (lepton number = 1) of either thermal or electron-capture origin.

The neutrinos produced during the core collapse are an important mechanism whereby energy is carried away from the core, without which, the succeeding neutron star could not form. The loss of the core's surrounding envelope is still caused by the shock of the initial core collapse and the rebound when the core cannot collapse further, due to nuclear forces.

 

[Chronos]

Here is an article that may be of interest; http://arxiv.org/abs/1402.4362, Problems with neutrino-driven core-collapse supernova mechanisms.

 

[Spinnor]

The neutrino cross section rises rapidly with energy, see below. With the graph below and some simplifications should you be able to come up with a rough estimate for the momentum transfer due to neutrinos.

Image from,

http://www.google.com/imgres?safe=o...hBwwCg&iact=rc&dur=737&page=1&start=0&ndsp=15

Is there such a thing as an index of refraction for a neutrino beam through matter?

Edit, I guess we need the neutrino cross section for iron nuclei?

 

[Spinnor]

In the rest frame of an escaping neutrino it "sees" a severe density increase in the matter because of a Lorentz contraction (in addition to already high densities), does this possibly increase the actual cross section?

 

[ChrisVer]

Not really iron (the external layers of a star should not be composed of iron). I guess the proton is enough.

As for the increase of density, I am not sure, but almost all neutrinoes are considered (in SM) to run at the speed of light, so Lorentz contraction is taken in account eversince we consider them...

I thought that the neutrino interaction with matter followed a logarithmic relation (with respect to energy). I am not sure how this came in my mind.

Does that mean that Ultra relativistic neutrinos leave a better/more clear signature when we measure them on earth? (if their energies allowed them to interact better with matter this must play a role in how we measure them here)

 

[Spinnor]

This is a quick and dirty estimate of the odds a super nova neutrino interacts on its way out.

Pack the matter of our sun into a shell of radius 1000km and thickness 1E-15m thick. We then have about,

[(2E30kg/sun)/(2E-27kg/proton)]/[4∏1E16cm^2] protons/cm^2 ≈ 1E40protons/cm^2

and as the cross section for a 30MeV neutrino is of order 1E-40cm^2 we should expect each neutrino to interact once on average on its way out of a super nova?

What amount of momentum can we expect on average to be transferred per neutrino?

Edit, the results depend strongly on the radius above, more care needed!

 

[ChrisVer]

In this I would question why doesn't the same mechanism/logic work with the sun neutrinos?
except for if their interaction rate grows really much with respect to energy... (from the graph I don't see such a relationship)

 

[mfb]

In the rest frame of an escaping neutrino it "sees" a severe density increase in the matter because of a Lorentz contraction (in addition to already high densities), does this possibly increase the actual cross section?

It also decreases the length of the material, keeping the area density the same => no.

Does that mean that Ultra relativistic neutrinos leave a better/more clear signature when we measure them on earth? (if their energies allowed them to interact better with matter this must play a role in how we measure them here)

All neutrinos we can measure (so far) are ultrarelativistic. For neutrinos of very high energy: yes. They are just much more rare.