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Asked by Harry to Daniel, Hannah, Maggie, Ry, Scott on 13 Nov 2017.
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Scott Melville answered on 13 Nov 2017:
This is a very good question! I can think of a couple of reasons:
(i) Depending on how the supernova happened, the neutrinos were likely produced BEFORE much of the light was, so they had a head start,
(ii) Neutrinos don’t really interact with anything, so they won’t be deflected by any of the charged gas that floats around outer space (but light will be slowed down a bit).The answer is certainly NOT that neutrinos faster than light – in fact, we believe that they travel just a little bit slower 🙂 (because they have a non-zero mass, but light is massless)
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Maggie Lieu answered on 13 Nov 2017:
That’s a very interesting question!
The reason is because at a supernova, the light and neutrinos usually need to push out from the surface layers of the star. Light can get absorbed and also bounce around and so it takes more time to push out. Neutrinos on the other hand can push right through, so they get a head start!
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Ry Cutter answered on 13 Nov 2017:
Both of these are great answers:
So I’ll talk about how we detect neutrinos.
Neutrinos are weakly interacting, this means they pass through most atoms without leaving a trace they were there! But it’s important that we we find a point where they do interact, this is where heavy water comes in! (Heavy water is water with two extra neutrons, one in each hydrogen). On the very rare occasion a neutrino hits one of these molecules a high speed electron is created. It moves so fast it can out pace light in the water, which creates Cherenkov radiation. Big detectors filled with heavy water are built to look for this blue light (see video) to find neutrinos passing through Earth!
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Hannah Middleton answered on 13 Nov 2017:
The other’s answers sound good! The neutrinos interact very very infrequently with matter, so they are not slowed down in the same way that light is.
In 1987 a supernova was observed relatively close by (just 168,000 light years away!!). Most of the neutrinos from that supernova just passed straight through the Earth. So of the many many neutrinos that were emitted, just 25 were picked up by the detectors on the Earth.
http://heritage.stsci.edu/1999/04/sn1987anino.html -
Daniel Williams answered on 13 Nov 2017:
I can’t add much to what everyone else said about neutrinos, but I’ll say something about gravitational waves. We recently saw an explosion caused by two neutron stars crashing into each other. We saw gravitational waves from that first, and then light (in the form of gamma rays) just under 2 seconds later. We think that probably happened because the explosion was opaque for that time – light couldn’t escape, but gravitational waves could.
I think it’s pretty likely that supernova do the same thing; neutrinos, like gravitational waves, aren’t really affected by normal matter, so they have a clear path, while light needs to battle its way through lots of material in its way.
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