The electron degeneracy pressure isn't overcome by gravity; the fusion point of carbon just happens to occur just before the gravity would have overcome the pressure. The key is that since the star is supported by the electron degeneracy pressure, which is unchanged by increased temperature, the WD won't expand and cool when the fusion runs too quickly, so you get the runaway reaction that detonates the star
(continued from previous) ... The point where the hydrogen recombines with its electrons is where the plateau in the light curve occurs and as recombination continues the H will become transparent and the remainder of the light curve is caused by the radioactive decay of elements that were formed and ejected from some of the deeper layers of the star. Again this isn't my area of specialization but that's the main process those types of supernova follow (according to current models at least)
Oh, so at the tipping point for a white dwarf all the 'interior' stored carbon spontaneously fuses as the electron degeneracy pressure is overcome by gravity (is that right?) It proceeds too quickly for any 'equilibrium' adjustment and so much more kinetic energy is produced.
When a supernova is observed how is it's type determined? Is it just based on the shape of the light curve? Is that actually how the different types are defined or is there more to it than that?
The shape of the light curve is part of it, but more significant is the spectrum of the light and what elemental spectral lines are present. For example in Type I supernovae there are no spectral lines from hydrogen, which makes sense for white dwarf supernovae because white dwarfs have already fused or ejected all of their hydrogen. In massive star supernova there are still strong hydrogen lines from their exploding outer layers. Since the different spectral features and the shapes of the light curves seem to be linked in these supernova types we can use both features together to confidently determine the supernova type
Most of the Type II supernovae are caused by the core collapse of high mass stars (10 - 40 Msun) rather than the white dwarf accretion described here. I'm not an expert in the exact details of this but my understanding is if the star still has mostly hydrogen in its outer layers (low metallicity) as these outer layers are blown off the H is heated and ionized (electrons escape). The H cools to the point where the electrons can be captured again (recombination) ... (continued)
How was it known that the supernova observed "in" the pinwheel galaxy was actually in it, and not somewhere between us and the galaxy? Same question for all other standard candles observed to figure out the distance to a galaxy.
A couple of reasons: first there are relatively few stars in the spaces between galaxies compared to the number of stars in the galaxies themselves. Even if there are tens of millions of stars between us and some background galaxies, it's much more likely that the supernova is from one of the hundreds of billions of stars in the galaxy itself. This probability is further increased when you consider that the stars in between galaxies are typically much older K and M type stars that are less likely to be going through supernova events (or contain Cepheid variable stars which would have likely all died out) Lastly, we can measure the redshift (which depends on how the object is moving) of the supernova and the galaxy it is in. If we see that they are moving in the same way that's further evidence that the supernova is actually in that galaxy. Good question!
The chart showed Type II-P remained at a constant luminous for 90 days, could you please enlighten me. Hahaha good time to use a pun I guess... But seriously what happen there?
The electron degeneracy pressure isn't overcome by gravity; the fusion point of carbon just happens to occur just before the gravity would have overcome the pressure. The key is that since the star is supported by the electron degeneracy pressure, which is unchanged by increased temperature, the WD won't expand and cool when the fusion runs too quickly, so you get the runaway reaction that detonates the star
(continued from previous) ... The point where the hydrogen recombines with its electrons is where the plateau in the light curve occurs and as recombination continues the H will become transparent and the remainder of the light curve is caused by the radioactive decay of elements that were formed and ejected from some of the deeper layers of the star. Again this isn't my area of specialization but that's the main process those types of supernova follow (according to current models at least)
Oh, so at the tipping point for a white dwarf all the 'interior' stored carbon spontaneously fuses as the electron degeneracy pressure is overcome by gravity (is that right?) It proceeds too quickly for any 'equilibrium' adjustment and so much more kinetic energy is produced.
When a supernova is observed how is it's type determined? Is it just based on the shape of the light curve? Is that actually how the different types are defined or is there more to it than that?
The shape of the light curve is part of it, but more significant is the spectrum of the light and what elemental spectral lines are present. For example in Type I supernovae there are no spectral lines from hydrogen, which makes sense for white dwarf supernovae because white dwarfs have already fused or ejected all of their hydrogen. In massive star supernova there are still strong hydrogen lines from their exploding outer layers. Since the different spectral features and the shapes of the light curves seem to be linked in these supernova types we can use both features together to confidently determine the supernova type
Ahh of course, that makes more sense. Thanks for the quick and detailed response. I'm enjoying your videos.
Most of the Type II supernovae are caused by the core collapse of high mass stars (10 - 40 Msun) rather than the white dwarf accretion described here. I'm not an expert in the exact details of this but my understanding is if the star still has mostly hydrogen in its outer layers (low metallicity) as these outer layers are blown off the H is heated and ionized (electrons escape). The H cools to the point where the electrons can be captured again (recombination) ... (continued)
How was it known that the supernova observed "in" the pinwheel galaxy was actually in it, and not somewhere between us and the galaxy? Same question for all other standard candles observed to figure out the distance to a galaxy.
A couple of reasons: first there are relatively few stars in the spaces between galaxies compared to the number of stars in the galaxies themselves. Even if there are tens of millions of stars between us and some background galaxies, it's much more likely that the supernova is from one of the hundreds of billions of stars in the galaxy itself.
This probability is further increased when you consider that the stars in between galaxies are typically much older K and M type stars that are less likely to be going through supernova events (or contain Cepheid variable stars which would have likely all died out)
Lastly, we can measure the redshift (which depends on how the object is moving) of the supernova and the galaxy it is in. If we see that they are moving in the same way that's further evidence that the supernova is actually in that galaxy.
Good question!
@@PhysicistMichael Thanks for the explanations! That seems reasonable to me. Also thanks for the very informative series!
Wow! M 101 has been busy lately. A new supernova was detected just this year! (2023).
The chart showed Type II-P remained at a constant luminous for 90 days, could you please enlighten me. Hahaha good time to use a pun I guess... But seriously what happen there?
How many times did you say "actually"?