B How are neutrinos distributed in the universe?

[newjerseyrunner]

@mfb mentioned in a thread about dark matter how neutrinos don't conglomerate in galaxies and it got me wondering where they are. Considering that they move at nearly the speed of light, I understand why they couldn't be captured by galaxies, but what about large scale structures? Do neutrinos pool in dense pockets of the universe, or are they more or less uniform? Google doesn't provide me with any links.

 

[mfb]

Unless you are close to a source (e. g. in a planetary system), the distribution of neutrinos from nuclear reactions is very uniform. The neutrinos are just too fast to be affected by gravity in any relevant way.
Primordial neutrinos might get slower today, but that depends on their unknown masses.

 

[Chronos]

Neutrinos are too 'hot' to clump by any known mechanism. A black hole might work, but, black holes have an annoying propensity to deconstruct things they capture. Neutrinos are strongly antisocial, they pass through other matter with great alacrity making it exceedingly difficult to slow them down.

 

[Chalnoth]

The distribution is highly uniform still, as the others above have mentioned. There are difficulties detecting the cosmic neutrino background directly, however, as the temperature of the neutrinos is currently about 1.95K. The Wikipedia article on the subject may be informative:
https://en.wikipedia.org/wiki/Cosmic_neutrino_background

 

[Orodruin]

As mfb has stated, relic neutrinos might cluster gravitationally depending on their masses. See for example: http://inspirehep.net/record/657114

 

[mfb]

PTOLEMY is a proposed experiment to detect the cosmic neutrino background, together with a highly accurate mass measurement. Clustering is also mentioned there.

 

[fresh_42]

PTOLEMY is a proposed experiment to detect the cosmic neutrino background, together with a highly accurate mass measurement. Clustering is also mentioned there.

How can they distinguish between relic, sun made and man made neutrinos? I guess our nuclear power plants also create a lot of them. (Sorry if this question is stupid or explained in the article.)

 

[Orodruin]

PTOLEMY is a proposed experiment to detect the cosmic neutrino background, together with a highly accurate mass measurement. Clustering is also mentioned there.

They only mention clustering in passing and cite the study I linked to, which is focused on gravitational clustering.

 

[Orodruin]

How can they distinguish between relic, sun made and man made neutrinos? I guess our nuclear power plants also create a lot of them. (Sorry if this question is stupid or explained in the article.)

All of these have very different energy ranges and/or concentration depending on the placement of your detector.

 

[mfb]

All of these have very different energy ranges and/or concentration depending on the placement of your detector.

And type. Fission-related neutrinos are antineutrinos which don't induce tritium decay. All other sources of man-made neutrinos are irrelevant unless you build your detector deliberately in a neutrino beam (like OPERA for example) - but those have GeV energies, compared to the meV energies of cosmic background neutrinos.