# Neutrinos penetration of neutron stars or white drawfs

• ensabah6
In summary, neutrinos can easily pass through solid objects like the Earth and even a light-year of lead would only stop about half of them. When it comes to something dense like a neutron star, the density of nuclear matter is about 10^15 times greater than ordinary matter, meaning that neutrinos would likely only penetrate about 10 meters into the star. This is supported by the fact that the mean free path of a neutrino in lead is about 22 light-years. There may not be a linear relationship between density and penetration, as there are additional factors such as the allowable final state of the neutrino in interaction with a neutron.

#### ensabah6

Neutrinos can pass through solid objects like the Earth easily, and a light-year of lead would only stop half of them from passing through.

What about something very dense like a white drawf or neutron star? How readily can neutrinos penetrate that? What % flux reduction would be achievable if neutrinos passed through a neutron star?

The density of nuclear matter is greater than the density of ordinary matter by about a factor of 10^15. So I would guess the answer would be that neutrinos would penetrate into a neutron star by roughly (1 light-year)*10^-15=10 m.

bcrowell said:
The density of nuclear matter is greater than the density of ordinary matter by about a factor of 10^15. So I would guess the answer would be that neutrinos would penetrate into a neutron star by roughly (1 light-year)*10^-15=10 m.
Is it the same for neutrinos and anti-neutrinos?

Bob S

bcrowell said:
The density of nuclear matter is greater than the density of ordinary matter by about a factor of 10^15. So I would guess the answer would be that neutrinos would penetrate into a neutron star by roughly (1 light-year)*10^-15=10 m.

thanks, according to this link it's 22 light years.

Neutrinos
This was an expected result, since the mean free path of a neutrino in matter is about 22 lightyears in lead and having the Earth in the path makes little ...
hyperphysics.phy-astr.gsu.edu/Hbase/particles/neutrino.html

I'm not sure there's a linear proportion of density and penetration.

From bcrowell:
The density of nuclear matter is greater than the density of ordinary matter by about a factor of 10^15. So I would guess the answer would be that neutrinos would penetrate into a neutron star by roughly (1 light-year)*10^-15=10 m.

From Bob S
Is it the same for neutrinos and anti-neutrinos?

ensabah6 said:
thanks, according to this link it's 22 light years.

Neutrinos
This was an expected result, since the mean free path of a neutrino in matter is about 22 lightyears in lead and having the Earth in the path makes little ...
hyperphysics.phy-astr.gsu.edu/Hbase/particles/neutrino.html

I'm not sure there's a linear proportion of density and penetration.
I think that a neutrino incident on a neutron has an allowable final state (proton plus electron), while the anti-neutrino incident on a neutron has none. This should be reflected in the total cross section.

Bob S

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Bob, Bob, Bob...<sigh>

Again, you are adding complications that are unnecessary and confusing.

The cross-section is what it is. If I have 1015 times as much material, the interaction rate goes up by this factor. This is all wrapped into the definition of a cross-section. Talking about the differences between neutrino-on-nucleon and antineutrino-on-nucelon is just muddying the waters.