# Neutrino Astronomy

Gold Member
The May 2010 issue of Scientific American had an article titled http://www.scientificamerican.com/article.cfm?id=through-neutrino-eyes". I enjoyed the article and read it several times.

It made me wonder though - how much energy in the form of neutrinos is passing through any given space? The Wikipedia article on http://en.wikipedia.org/wiki/Neutrino" [Broken] cites a reference stating that there are 50 trillion neutrinos passing through our bodies every second. Is there an estimate of how much energy this is equivalent to?

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From the sun

http://www.physics.ox.ac.uk/neutrino/sno/std2.gif [Broken]

as you see the wast majority of that flux is from the pp reaction, corresponding to neutrinos between 0.1 to 0.3 MeV - I think you can use 0.2 MeV as the means neutrino energy if you want.

Good luck

the neutrino flux is not constant over the entire universe.. or well the cosmic neutrino bkg is... but they have like 2 eV energy or so

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Gold Member
From the sun

http://www.physics.ox.ac.uk/neutrino/sno/std2.gif [Broken]

as you see the wast majority of that flux is from the pp reaction, corresponding to neutrinos between 0.1 to 0.3 MeV - I think you can use 0.2 MeV as the means neutrino energy if you want.

Good luck

the neutrino flux is not constant over the entire universe.. or well the cosmic neutrino bkg is... but they have like 2 eV energy or so

OK, let's see if I can get this right.

Average neutrino energy - .2 Mev - 2x10^5 ev
5x10^10 neutrinos passing through a human body every second
1x10^15 ev per second.

Dividing by 1 Watt ~6.24x10^18 eV/s

1.6x10^-4 Watts
= .16 milliwatts

Does that look correct?

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Chronos
Gold Member
Neutrinos are immensely abundant in the universe, enough so they were candidates for the missing mass before we arrived at the dark matter hypothesis. We since determined their numbers were far short of that necessary to account for dark matter.

13.824 watts per day avg of solar neutrinos. Not including neutrinos created by nuclear decay on earth or proximity to nuclear reactions.

The questions are:

1) How much mass were they considering the average human to have?
2) Does proximity to the sun, as in global positioning affect the amount that passes through us per day?
3) Does time of day affect the amount of neutrinos passing through us? (excluding night hours)
4) Do neutrinos lose any measurable amount of energy when passing through objects/bodies?
5) Based on past and current testing methods, what byproducts do we get other than argon when attempting to collect/measure neutrinos?

2) Does proximity to the sun, as in global positioning affect the amount that passes through us per day?

It's a 1/r^2 thing

3) Does time of day affect the amount of neutrinos passing through us? (excluding night hours)

Not by much. At night, the neutrinos go through the earth and head out the other end.

4) Do neutrinos lose any measurable amount of energy when passing through objects/bodies?

Not unless the interact with something, which doesn't happen very often.

5) Based on past and current testing methods, what byproducts do we get other than argon when attempting to collect/measure neutrinos?

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

The newer detectors use large pools of underground water and detect Cernekov radiation.

One "missed opportunity" was that if SN 1987A happened today, we would be in a lot, lot better position to do neutrino detection. I think that about a dozen neutrinos from SN 1987A were detected which was actually a really big deal. Today, I think we'd be able to detect hundreds and get things like energy and direction measurements. However 1987A was a really big deal, because had the detectors seen nothing, then it would be a sign that our understanding of supernova was even worse than we thought.

Now if you have an supernova happen in our galaxy then the number of detections would be quite high. Something that *could* happen is that you could have a supernova go off in our galaxy which we can't see visually (because it's behind some dust cloud or on the other side of the galactic core), but which we'd detect only through neutrinos.

But I hope this doesn't happen until we get the gravity wave detectors really cranking. Again, having a detector there is useful, because if you see nothing, this means something.

Also, a lot of these detectors were originally designed to detect proton decay, and since we haven't see protons decay, this is also a big deal.

Gold Member
One "missed opportunity" was that if SN 1987A happened today, we would be in a lot, lot better position to do neutrino detection. I think that about a dozen neutrinos from SN 1987A were detected which was actually a really big deal. Today, I think we'd be able to detect hundreds and get things like energy and direction measurements. However 1987A was a really big deal, because had the detectors seen nothing, then it would be a sign that our understanding of supernova was even worse than we thought.

Now if you have an supernova happen in our galaxy then the number of detections would be quite high. Something that *could* happen is that you could have a supernova go off in our galaxy which we can't see visually (because it's behind some dust cloud or on the other side of the galactic core), but which we'd detect only through neutrinos.

But I hope this doesn't happen until we get the gravity wave detectors really cranking. Again, having a detector there is useful, because if you see nothing, this means something.

It's an exciting time in Astronomy. It wasn't so long ago that the existance of neutrinos was being debated and now telescopes are being built to detect them. We can now directly measure processes occurring at the center of stars. Very fascinating science.

Not by much. At night, the neutrinos go through the earth and head out the other end.

Actually, if we're tracking neutrinos by looking for the creation of and presence of argon/germanium, would it not stand to reason that during the passage through the earth, the "neutrino stream" would deteriorate by combining with earth materials?

I have to say, this is fascinating to me.

Actually, if we're tracking neutrinos by looking for the creation of and presence of argon/germanium, would it not stand to reason that during the passage through the earth, the "neutrino stream" would deteriorate by combining with earth materials?

Yes but not by much. I don't have the numbers with me, but you are talking about on the order of several billions of neutrinos going through the earth with maybe a few thousand interacting with it. (Those are extremely rough numbers. The actual number of neutrinos that went through the earth and the number of neutrinos that react with the earth is something that would make a nice intro astronomy homework problem.)

Something else that is interesting is that the instruments for neutrino detection are also used to try to detect dark matter either directly or indirectly (http://www.snolab.ca/public/science/index.html [Broken])

http://www-astro-theory.fnal.gov/Conferences/TeV/Bauer.pdf

http://cdsweb.cern.ch/record/445728/files/0007003.pdf

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So what has long been suspected has recently been "officially announced" - ie. that neutrinos have mass, due to confirmation of their flavor oscillation.

So what are the consequences of this discovery?

what does neutrino mass allow us to further investigate? What new questions does it raise?

How can we measure or derive the neutrino's mass value?

Can neutrinos be used for any practical applications? Would the discovery of their mass and flavor oscillation enable any new applications that weren't previously considered? I'd read that the US Navy was researching neutrinos for submarine communications. I'd likewise wonder if neutrino communications might not also be useful for subterranean communications, for example if probe was exploring underground caves on the Moon, Mars, etc.

I had also read that neutrinos could be used for geophysical measurements, if intense neutrino sources could be developed. Presumably, this could be applied to other astronomical bodies as well, besides our own Earth (eg. the Sun, or other planets)

Would it also be possible to use distant stellar neutrino sources to make astrophysical measurements? If known neutrino sources were eclipsed or occluded by some astrophysical body, then differential measurements could be analyze to determine useful characteristics about that body.

What situations lend themselves towards exploiting the characteristics of the neutrino for measurement purposes? What can neutrinos usefully do that photons would be problematic on?

So far, photons seem to have been our main tool for exploring the wider universe at large.
But of course photons have strong interaction with matter, which neutrinos don't, so that perhaps neutrinos can be used to probe much larger quantities of matter (nebulae? stars? black holes?)

Since exo-planets are of major interest these days, and they typically orbit stars which happen to be major neutrino sources themselves, could neutrino flux be used to measure characteristics of interest for exo-planets?

Given the role of neutrinos in decay reactions, how can this be used to extract new information on astrophysical bodies? What types of astrophysical bodies or phenomena would neutrinos be best suited to analyzing?

How can we build more sensitive/effective neutrino detectors/emitters/instrumentation in order to make better use of neutrinos?

I once had an idea that fullerene buckyonions could be used to crowd/concentrate electronic charge at their interiors, because their exterior surface area is significantly larger than their interior surface area, which might permit an "hydraulic effect" through "radial polarization".
ie. if you surround the buckyonion's exterior with negative charge (anionic solution?), then the buckyonion's electrons would migrate inwards, concentrating them towards the interior. I couldn't figure out a useful application for concentrating electronic charge like this, until years ago when I saw a publication by a Prof Ohtsuki of Japan:

http://prl.aps.org/abstract/PRL/v98/i25/e252501

http://www.phys.ncku.edu.tw/mirrors/physicsfaq/ParticleAndNuclear/decay_rates.html

http://www.hps.org/publicinformation/ate/q7843.html

the most dramatic radionuclide in this regard has been rhenium-187, for which a remarkable reduction in the half-life from 4.1 x 10^10 years to about 33 years has been observed.

Now that's a major change!

If beta-decay rates can be affected by electron density, then could the supplementation of neutrino flux likewise affect beta-decay? Could some compact/efficient instrument be built around electron-stripped rhenium-187, to detect neutrino flux changes with high sensitivity?