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peteshimmon
2008-May-09, 05:46 PM
This is an offshoot of my ATM ideas for anyone
who remembers but it is mainstream stuff and I
think justified in this forum. I have been
wondering for a while if white dwarfs near
ordinary mainstream stars are absorbing much
energy from the neutrino wind passing through
from the nuclear reactions in the star. I tend
to think that the density of matter in white
dwarfs coupled with the energy gain in falling
onto these stars means that a not insignificant
number of neutrinos react inside the dwarf
releasing energy that has to difuse out along
with the original energy the dwarf started
with. The end question here is has it been
determined that such dwarfs appear brighter
than isolated white dwarfs?

The maths involved is way beyond my ken, books
on "radiation transport" are dense with
equations. I just point out the possibilities.

There seem two basic mechanisms, neutrinos
hitting electrons giving off photons and
nuclear reactions with nuclei of atoms. I
tried google for any hint of any historical
investigations but found nothing.

One very interesting possibility is the exit
of neutrinos from the far side of the dwarf.
Any radiation generated here is free to
escape. And it will be relativistically focused
in the direction the neutrinos were going.
Those that passed through a thin chord at the
side of the dwarf will have to climb out the
gravitational field and will be deflected
sideways. And the neutrinos are not all from
the exact centre of the main star. So the weak
beam is not too narrow.

So I wonder if x-ray transients that have
symmetrical rise and fall profiles are
routinely observed? This is a possible model I
think. Is it original?

peteshimmon
2008-May-16, 05:56 PM
Well the questions and the possibilities have
been put. I am not sure if my notions of energy
diffusing out of white dwarfs the same as
ordinary stars is naive but they are said to
cool down! And something will happen to a
fraction of neutrinos.

In the annals of theorectical astronomy, I am
sure some highly trained person has looked at
this sometime.

Zachary
2008-May-17, 12:24 PM
Just a hunch but I reckon the energy from the ordinary solar wind colliding with the dwarf star would release more energy than the neutrino wind. But then again I can't prove this :)

Zachary
2008-May-17, 12:34 PM
http://en.wikipedia.org/wiki/Image:Bahcall-Serenelli_2005.jpg

I was trying to find out the average neutrino flux from our Sun so a rough value of the energy it could provide a white dwarf star with could be worked out (assuming 100% efficiency, which is a bit rich but hey, 'tis a start), but that's the best I could find. It's a graph of neutrino flux against energy for our sun (predicted from the standard model, not experimental data though).

trinitree88
2008-May-17, 06:58 PM
http://en.wikipedia.org/wiki/Image:Bahcall-Serenelli_2005.jpg

I was trying to find out the average neutrino flux from our Sun so a rough value of the energy it could provide a white dwarf star with could be worked out (assuming 100% efficiency, which is a bit rich but hey, 'tis a start), but that's the best I could find. It's a graph of neutrino flux against energy for our sun (predicted from the standard model, not experimental data though).


Zachary. You mention neutrinos hitting electrons. In the electromagnetic interaction, a high energy photon can hit an electron and speed it up...Compton scattering....and the photon is redshifted. But neutrinos do not participate in the electromagnetic interaction or the strong interaction, only the weak interaction. Here, they can act via the two charged currents W+, or W-, or the neutral current Z0. The emission of any of the three will redshift the neutrino, so it "looks" like the same thing externally, but the carrier in the Compton scatter is a photon, so they're distinct.
Yes the white dwarf can pick up some neutrino energy, and a subtle effect might show with a periodicty related to the revolution period. It seems from the SNO day/night periodicity that the Earth is sufficiently massive to show a ~14% change in reaction rates, which through scattering would represent ~ a 10 % energy drop for scattered neutrinos. Say the central star emitted 10 Mev neutrinos. If each scattered once, that would drop their average energy to ~ 9 Mev (James Losecco,Head, Dept. of Physics Univ. Notre Dame). The neutrino cross-section varies as the ~ square of the energy (Ultimate Neutrino Page)...so 92 compared to 102...is 81 to 100. Roughly an order of magnitude answer.
Your dwarf only intercepts a small fraction of the central companion's neutrinos though, and you need to approximate it's subtended angle in the sky using an assumption of isotropic emission (not quite true, but will suffice for OOM calculations). ....and remember you have a sphere, not a disk.
It will not have much effect on a young white dwarf, as the energy emission scales as (Kelvin)4thbut will contribute to a cooling anomaly in an old cold one....the dang thing will seem to be fusing slowly.:shifty::think: :doh: pete

peteshimmon
2008-May-18, 05:32 PM
Thanks for taking an interest. That neutrino
diagram is still not fully confirmed
experimentally I understand though the latest
detectors are showing more details. I would
naturally defer to your comprehensive
understanding, Trinitree, I just try to
extrapolate from known facts.

Many eclipsing binaries have white dwarfs
orbiting bright stars, some of greater mass
than the sun with greater theoretical neutrino
fluxes. I thinks the flux passing through the
dwarf in one direction will, as some energy in
released in interactions, cause some "sound"
waves to propagate to the exit side. If this
causes material to "jump" from the exit side
I would say photons would be generated from
the normal mode of accelerating electrons. This
would be omnidirectional emmision I think.

We know that anti neutrinos are detected by
Cherenkov light generated when an electron is
kicked in the water of the detector. Surely
this happens writ large in the white dwarf
interior. In addition there are nuclei that
react. Sometimes.

I repeat that falling on degenerate stars gives
extra energy to particles making reactions
more likely.

Whatever does happen, I think observations may
have shown x-ray beams emanating from dwarfs
passing in front of stars. There was a famous
transient in the mid seventies seen by the
British X5 craft. A slow rise and fall of
energy from a star. This might be an answer.

Hornblower
2008-May-20, 02:34 AM
Why all the fancy stuff? We all know that neutrinos penetrate where nothing else can do so. If a few are stopped deep inside a white dwarf, I would expect the energy to be thermalized and just make the star a bit hotter.

peteshimmon
2008-May-20, 05:15 PM
Well its just that astronomy might be missing
a few tricks here. A few observable tricks!