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Comment by shifto | Hacker News Reader

Not really related but I like how they are trying to detect neutrinos to discover a supernova before it happens [1]. As the neutrinos leave the star hours before they collapse (because the neutrinos can easily escape the star due to it's low mass).

[1] https://en.wikipedia.org/wiki/SuperNova_Early_Warning_System

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A small correction- it’s not the small mass of the neutrino that allows it to escape quickly, but the fact that they are electrically neutral, and also do not interact with the strong force and do not get caught by the nucleus of atoms. Photons have no mass, but they arrive after the neutrinos because they are slowed down by being constantly absorbed and remitted by the atoms of the star through the electromagnetic force.

Thanks for clarifying!

Do you think neutrinos could be used to produce electricity?

For the sun it's probably easier to capture the 98% of energy that's radiated as light.

The sun is by far the best source of neutrinos.

For a standard core collapse supernova, the vast majority of the released energy is in the form of neutrinos.

That always astounded me: Neutrinos hardly interact at all, but as I understand supernovas it is the neutrinos that cause all the outer layers of the star to blow off at high speed. Supposedly some of the elements heavier than iron get formed by fusion during that explosion. That's a lot of energy transferred to a lot of mass just from neutrinos. So, that's a LOT of neutrinos.

The actual source of the neutrinos is what, something about making a neutron star out of the iron core of the star? Would that be too many neutrinos for just the iron core?

I'm no expert, but as far as I'm aware it's a combination of beta decay and thermal neutrino pair production.

Thanks!

They are primarily coming from neutron capture (electron + proton -> electron neutrino + neutron). During much of the collapse even these weakly-interacting neutrinos get trapped behind the high-density shock wave. As it expands and the density becomes lower, they escape in what's known as the neutronization burst.

Thanks. Makes sense: The big push, e.g., the shock wave, is not all just directly from just the neutrinos from just the collapsing iron core. Thanks.

Because they are electrically neutral, and do not interact with electromagnetic fields, it would be quite hard.

Well, generally speaking, in the world of elementary particles there may be other kinds of interactions (and decay paths) as well as the good old mechanical energy - all waiting to be converted into the electromotive force.

Are there new types of interactions underway that may make neutrinos interaction feasible?

Thing is, neutrinos hardly interact with anything at all, we need huge sensors just to detect a few signals once in a while so they would be na horribly inefficient way to capture energy.

A hypothetical idea is to direct a neutrino beam at the core of a pulsating star, which modulates its frequency and allows for efficient interstellar communication.

https://www.economist.com/science-and-technology/2011/04/07/...

https://arxiv.org/pdf/0809.0339.pdf is the paper

Thank you. When supernova 1987A was first detected, I thought I recalled reading an article that talked about how we detected neutrinos from it ~1hr before its visible light. I thought I was misremembering this, but apparently not.

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