Why so little neutrinos?

  • #1
If the sun produces so many neutrinos from fusion, then I would assume that so do all other fusion stars, yet why is it that our detectors detect only the number of neutrinos that would be expected to be produced from our sun? If neutrinos travel at nearly the speed of light and barely ever interact with anything, then shouldn't we be constantly bombarded by an endless number of them coming from the trillions of stars in the universe?
 

Answers and Replies

  • #2
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I think this is basically the same question as in Olbers paradox - if there are so many stars out there, why is the sky not bright in the night ? you just ask the question for neutrinos instead of photons.

maybe we should call this one "moe darklights paradox" ?
 
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  • #3
malawi_glenn
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yes, it is basically the same question.

It is also related to intensity and flux. A star 5Ly away will radiate over the whole solid angle and only a tiny tiny tiny tiny fraction will reach earth, and only a tiny tiny tiny fraction will interact here. So the main component of neutrino flux here on earth is our star the sun.
 
  • #4
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Neutrino telescope?

I can understand why our sun would be the largest source of neutrinos that we can "see", but all other stars should also produce neutrinos, but to us not in the quantity as from our sun.

This brings up a question I have. Since neutrinos are "particles", is it possible to build something like a "neutrino telescope"? With enough resolution, it might be possible to identify those sources with greater or lesser amounts of neutrino emission. Would this be another way to look at our universe? Does anyone know of anything being done along these lines? I'm aware of the various mines that have been converted into neutrino detectors, but to my knowledge, they're not particularly directional in nature, but I could be wrong.

Thanks.
 
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  • #5
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I can understand why our sun would be the largest source of neutrinos that we can "see", but all other stars should also produce neutrinos, but to us not in the quantity as from our sun.

This brings up a question I have. Since neutrinos are "particles", is it possible to build something like a "neutrino telescope"? With enough resolution, it might be possible to identify those sources with greater or lesser amounts of neutrino emission. Would this be another way to look at our universe? Does anyone know of anything being done along these lines. I'm aware of the various mines that have been converted into neutrino detectors, but to my knowledge, they're not particularly directional in nature, but I could be wrong.

Thanks.
The problem is, that neutrinos only interact VERY weakly with ordinary matter. Even from the sun we do not catch very much neutrinos in this detectors (though enough to have fun with them and verify our theories about how the sun is working). But as far as I know from normal stars there is currently no chance to catch any neutrinos. But in case of a supernova there are so much neutrionos emitted (I think the "neutrino luminosity" of a supernova is even bigger than the luminosity in the visible spectrum) that we can detect them. One of the early detectors just went operational just before SN1987 went KAWOOM, (or, more correctly, just before the light and the neutrinos from this explosion reached us), so the guys who built it were very happy about the many neutrinos they caught from this supernova.
 
  • #6
mgb_phys
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I can understand why our sun would be the largest source of neutrinos that we can "see", but all other stars should also produce neutrinos, but to us not in the quantity as from our sun.
Correct - but like Olbers paradox they should produce them in the same proportion as the light from the other stars compared to the sun. (that was really badly phrased!)

This brings up a question I have. Since neutrinos are "particles", is it possible to build something like a "neutrino telescope"?
The kamiokande detector is somewhat directional - using cerenkov radiation from the particles. The cl->ar detectos aren't
 
  • #7
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I thought the neutrinos change type at random
and that limited the detection rate
 
  • #8
Nabeshin
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In reference to the Obler's Paradox type situation, I think the solution would be much the same as it is in reference to light. The universe is not infinite and therefore is not infinitely old, therefore light (or neutrinos) from all the stars has not had a chance to reach us.
 
  • #10
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In reference to the Obler's Paradox type situation, I think the solution would be much the same as it is in reference to light. The universe is not infinite and therefore is not infinitely old, therefore light (or neutrinos) from all the stars has not had a chance to reach us.
but for the light from stars which is reaching us? together with light,we should also find neutrinos?isn't?
 
  • #11
malawi_glenn
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but for the light from stars which is reaching us? together with light,we should also find neutrinos?isn't?
'


Yes but the neutrinos interfear so incredible little, their cross section is of the order 10^-20 Barns! Photon has high cross section.
 
  • #13
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Thanks

You may find this of interest;


A neutrino telescope planned for construction under the Mediterranean.
Yes, very interesting. Thank you.
 
  • #15
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neutrinos are extremely difficult to detect - they were thought of as massless particles but recent work suggests that neutrinos possess a very small mass.

I dont understand the comparison made to the night sky being filled with light at night because of the number of stars.

Remember that's the point - if the universe was infinite then the night sky would be filled with light from the INFINITE number of stars out there. This is strong evidence that there are a finite number of stars out there and that the universe is almost entirely composed of non-baryionic material (about 70% dark energy and 25% dark matter.

As EInstein said "the universe is FINITE but UNBOUNDED"
 
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  • #16
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'


Yes but the neutrinos interfear so incredible little, their cross section is of the order 10^-20 Barns! Photon has high cross section.
Is a "Barn" a standard unit of measurement?

Chuckle, thanks for a good laugh!
 
  • #18
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Live and Learn, I always say. Thanks for letting me know that there really is a BARN in quantum mechanics. Now I'm getting an even better chuckle out of my ignorance!
 
  • #19
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i thought that we were being constantly being bombarded by neutrinos,you should read the book SPACESHIP NEUTRINO (no it's not a picture book)
 
  • #20
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i thought that we were being constantly being bombarded by neutrinos,you should read the book SPACESHIP NEUTRINO (no it's not a picture book)
I thought we were, also. Can you shed a few sentences from your reference?

Thanks.
 
  • #21
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umm i don't have the book in front of me, i read it about a year ago, and my school library is closed. But it's in the first ten pages (near the beginning) just google neutrinos or wikipedia it.
rubecuber
 
  • #22
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i thought that we were being constantly being bombarded by neutrinos,you should read the book SPACESHIP NEUTRINO (no it's not a picture book)
Yes, we are constantly constantly bombarded by them - but all (or nearly all) of them are coming from our sun. But Moe Darklights question was, why dont we receive more neutrinos from the stars, if there are so many stars out there.
 

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