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MichaelC
2007-Aug-14, 11:55 AM
When everybody talks of a star exploding, I have never heard anybody mention the period of time that it takes to expand.
Are we talking about, say exploding from the surface to a one million mile range, in seconds, hours, or days? Just how powerful is this force?

antoniseb
2007-Aug-14, 12:34 PM
When we look at the Crab Nebula, we see something about a light year across, and the light from the explosion got to us about a thousand years ago (953 years ago). So, the forward bulky materials (not counting cosmic rays) were moving at about .0005 times the speed of light.

Other SN remnants may be faster or slower depending on SN type etc, but they should all be within a power of ten of this.

StupendousMan
2007-Aug-14, 12:59 PM
When everybody talks of a star exploding, I have never heard anybody mention the period of time that it takes to expand.
Are we talking about, say exploding from the surface to a one million mile range, in seconds, hours, or days? Just how powerful is this force?

Typical ejecta velocities during the first few weeks of an explosion range from 5,000 km/s to 20,000 km/s; the fastest material is moving at almost 10 percent the speed of light.

Hmmm, in order to travel one million miles, how long would it take ... (gets out calculator) ... about 2 or 3 minutes.

Tim Thompson
2007-Aug-16, 12:27 AM
Probably more than you ever wanted to know about core collapse supernovae: Theory of core-collapse supernovae (http://adsabs.harvard.edu/abs/2007PhR...442...38J), Junka, et al., Physics Reports 442(1-6): 38-74, April 2007. It only takes about 0.1 seconds for the core to collapse from a radius of about 3000 km to a radius of about 10 km, and then rebound. The shock has to travel outwards through infalling material, and less sophisticated models don't explode at all. But I think the shock will propagate through the star to initiate a visible explosion within a few minutes to an hour at the most. The delay between the neutrinos & optical burst of SN 1987A would indicate that time scale, but I don't recall what it was at the moment. As others have shown, once the explosion breaks out, expelled material moves along rapidly.

trinitree88
2007-Aug-16, 01:49 AM
When everybody talks of a star exploding, I have never heard anybody mention the period of time that it takes to expand.
Are we talking about, say exploding from the surface to a one million mile range, in seconds, hours, or days? Just how powerful is this force?

MichaelC;1048816. The highest published velocity I've seen is for SN1987a, by Alexei Fillipenko...25,000 + or - 5,000 km/sec for the ejecta (Ap. J, I believe). The overall energy of large type 2's runs about 2 times 1053 ergs. If the ejecta actually reaches Fillipenko's upper limit, it means several percent of the total energy comes out as kinetic energy in the ejecta.
Earlier models had ~ 99% as neutrinos, but that's been toned down some in recent years. The prompt neutrino burst still dominates the energy release though. This carries over to other extreme interactions...if it's occuring in the hundreds of millions of Kelvins....it's going to produce mostly neutrinos as a consequence of decay cascades. This makes it tricky to produce hot quark/gluon fireballs, as the energy wants to radiate away as neutrinos rather than accumulate for an appreciable length of time.:(