Gannet said:I was wondering for the majority of the projectiles from supernova what would be roughly their velocities. Has anything been determined or theorized?
Thanks in advance
nismaratwork said:That really depends on what you mean by projectile, and the type of supernova. A somewhat glib answer would be "the speed of light", as photons and neutrinos far outnumber iron or helium molecules being blown out from the shockwave.
The stages of a SNR's life represent an area of current study; however, basic theories yield a three-phase analysis of SNR evolution.
(1) In the first phase, free expansion, the front of the expansion is formed from the shock wave interacting with the ambient ISM. This phase is characterized by constant temperature within the SNR and constant expansion velocity of the shell. It lasts a couple hundred years.
(2) During the second phase, known as the Sedov or Adiabatic Phase, the SNR material slowly begins to decelerate by 1/r(3/2) and cool by 1/r3 (r being the radius of the SNR). In this phase, the main shell of the SNR is Rayleigh-Taylor unstable, and the SNR's ejecta becomes mixed up with the gas that was just shocked by the initial shock wave. This mixing also enhances the magnetic field inside the SNR shell. This phase lasts 10,000 - 20,000 years.
(3) The third phase, the Snow-plow or Radiative phase, begins after the shell has cooled down to about 106 K. At this stage, electrons begin recombining with the heavier atoms (like oxygen) so the shell can more efficiently radiate energy. This, in turn, cools the shell faster, making it shrink and become more dense. The more the shell cools, the more atoms can recombine, creating a snowball effect. Because of this snowball effect, the SNR quickly develops a thin shell and radiates most of its energy away as optical light. The velocity now decreases as 1/r3. Outward expansion stops and the SNR starts to collapse under its own gravity. This lasts a few hundreds of thousands of years. After millions of years, the SNR will be absorbed into the interstellar medium due to Rayleigh-Taylor instabilities breaking material away from the SNR's outer shell.
Astronomers working with HUT have also calculated the speed of a shock wave plowing through interstellar space from the Cygnus Loop, a supernova remnant about 26,000 light-years from Earth. The supernova's shock wave proved energetic enough to strip five of eight electrons from atomic oxygen gas and induced these ionized atoms to emit the ultraviolet light detected by HUT, reports Arthur F. Davidsen of Johns Hopkins University. Equating the energy of the emitted ultraviolet light with the kinetic energy of the passing shock wave, Davidsen's team estimates that the wave was speeding along at 168 kilometers per second.
The explosion expels much or all of a star's material at a velocity of up to 30,000 km/s (10% of the speed of light), driving a shock wave into the surrounding interstellar medium.
Type Ia Lacks hydrogen and presents a singly ionized silicon (Si II) line at 615.0 nm (nanometers), near peak light.
Type Ib Non-ionized helium (He I) line at 587.6 nm and no strong silicon absorption feature near 615 nm.
Type Ic Weak or no helium lines and no strong silicon absorption feature near 615 nm.
Type IIP Reaches a "plateau" in its light curve
Type IIL Displays a "linear" decrease in its light curve (linear in magnitude versus time).
nismaratwork said:That really depends on what you mean by projectile, and the type of supernova. A somewhat glib answer would be "the speed of light", as photons and neutrinos far outnumber iron or helium molecules being blown out from the shockwave.
twofish-quant said:The picture that you should have is a shock wave, and not of projectiles. Everything is a gas, and the fastest things can travel for extended periods of time is the sound speed. Anything that travels much faster than the sound speed will get slowed down with shocks.
More accurately the gas moves roughly at the speed of sound. Near the core the speed of sound is roughly one tenth the speed of light. Once you get into the interstellar medium, the speed of sound drops considerably. The speed of sound is roughly sqrt(gamma pressure / density).
Some wikipedia pages
http://en.wikipedia.org/wiki/Shock_wave
http://en.wikipedia.org/wiki/Rankine–Hugoniot_conditions
http://en.wikipedia.org/wiki/Blast_wave
(Also I'll likely be adding something for the Sedov blast wave solution and rewriting the Hugoinot conditions page. Both are cool because you can get a lot with some simple algebra).
nismaratwork said:Yep, that's pretty much how I see it, but again a huge portion of what actually escapes are neutrinos, and photons, which tends to be more "jet-like".
Neutrinos in particular are ejected in an asymmetric fashion
That really depends on what you mean by projectile
There's a trick some people use in this forum: if they want to learn about supernova remnants, they ask about supernova remnants. Try it next time.I was hoping to learn about supernova remnants (SNRs) at the chunk (macro) level.
twofish-quant said:That's not likely to be the case. The neutrino and photon fields are a lot more smooth and symmetric than the gas. It's the gas that forms jets. Baryonic matter tends to clump whereas photons and neutrinos tend not to, and so when you do the calculations the neutrinos and photons are a lot more smooth than the gas.
One way of thinking about it, is try to build a doghouse out of neutrons and protons. Not hard. Now try to build a doghouse out of neutrinos or photons. It's really hard to get neutrinos and photons to clump together.
Also internal of the star is optically thick, which means that the photons are pretty much trapped with the gas until the shock wave hits the surface.
They aren't in any of the simulations that I am aware of. There are huge asymmetries but those are mostly in the gas field.
nismaratwork said:I should clarify this, I don't mean that there are polar jets of neutrinos, but that anisotropy in neutrino emission helps to drive the jets you describe.
There are asymmetries of the production of flavor of neutrino and oscillation.