do supernova events issue observable precurrsors

[timetraveller]

hi guys I was recently reading some articles,about supernova events during which a thought popped into my head, which i thought i might ask for comments on here, which is Prior to and during the supernova event is there any precursory evidence that the supernova is about to happen. If you think about it logically, as the star begins its inwards collapse the gravitational effect must start to increase exponentially due to the increasing density of the mass. This surely would mean an increasing warping effect on the surrounding space and if this was the case then the effects of that increasing warpage should be detectable in some way, increased gravitational effects on nearby bodies or gravitational lensing . I am assuming of course that the gravitational collapse occurs over a finite period of time and is not instantaneous would appreciate your thoughts and comments

regards timetraveller

[acey]

First sign of a supernova event is neutrino emission. Collapsing supernovae are so dense that light and heat have a hard time getting out, but neutrinos barely interact with anything at all so they get out easily, and they travel at very close to the speed of light. So across the distance to Earth, the neutrinos are still able to win the race.

Not sure about gravitational warping etc. A collapsing star doesn't get any heavier, so objects orbiting it wouldn't notice a difference - until they get fried, of course. And gravitational effects propagate at light speed, so graviational waves etc couldn't reach other bodies (including Earth) any faster than the light of a supernova.

[dogfish]

Acey is right. I was reading something in this month's Astronomy Now that says Neutrino's precede the light emitted by a few hours. The Neutrino burst results from the increase in temperature of the collapsing star when it runs out of fuel. It is the increase in temperature that causes protons and electrons to merge (leading to the Neutron core), shedding Neutrino's in the process. It's the remaining elements, collapsing into the core and then rebounding, that cause the visible flash of a supernova.

I hope I've remembered that correctly - someone please tell me if I've got it right.

Cheers, Martin

[acey]

That's pretty much what I remember too. The resulting neutron star continues to shed the bulk of its energy via neutrinos rather than photons - the crust of a neutron star is solid iron. Some years ago there was a supernova in one of the Magellanic Clouds and neutrino detectors on Earth gave warning of it - I guess this is the routine way of looking for events now. The time lag would obviously depend on the distance of the object, and presumably gives a way of measuring that distance.

Andrew

[coatesg]

First sign of a supernova event is neutrino emission. Collapsing supernovae are so dense that light and heat have a hard time getting out, but neutrinos barely interact with anything at all so they get out easily, and they travel at very close to the speed of light.

Interestingly, though neutrinos hardly interact with anything, there is theory that the interaction of the neutrinos with the star's atmospheres (at high density and high energy) causes the star to actually be destroyed rather than the outer layers just stalling. Not sure that the details have been fully ironed out though this paper looks quite good (though a heavy read for lunchtime!):

http://arxiv.org/PS_cache/astro-ph/pdf/0612/0612072v1.pdf

The theory for the creation of neutrinos (as dogfish says) is through electron-proton combination (inverse beta-decay through the weak interaction), which is energetically favourable due to the high density, but mostly through thermal neutrino/anti-neutrino pair production. The new core cools through neutrino emission (since the core stops being opaque to neutrinos before it stops being opaque to light) and the majority escape to space. The ones that do interact with the outer layers of the core and the outer layers of the star cause the stalled shock from the core bounce and the outer layers to stop falling inwards and the explosion to be "kicked off".

EDIT: Correcting a slight snafu in the "opaque" sentence...