Astrophysics late burning stages and supernovae 1) What are the stages of nuclea

Question

Astrophysics late burning stages and supernovae

1) What are the stages of nuclear burning that take place after He burning in massive stars, their characteristic temperatures, lifetimes, and nucleosynthetic products?

2) Late burning stages have approximately the same amount of energy available per gram of fuel, yet the lifetimes are much shorter. The reason for this is neutrino cooling. Eplain why neutrino cooling makes such a difference.

3) Why does nuclear burning end when the core is mainly iron?

4) Neutrino-driven supernova mechanism - explain how the shock is launched, why it stalls, how it gets restarted, and how energy is transported.

5)  Qualitatively describe QSE, NSE, and the r-process and list what elements they produce.

Explanation / Answer

Stages

1 day nickel 56, Iron

2. The neutrino cooling is the process by which the neutrons and neutrinos are formed by combination of proton and electrons. the process is called neutronization where the net charge is zero since neutron has no charge. since the neutrino formation happens by absorbing heat energy from the sorroundings and as result the temperature reduces. ((neutron formation is the theory behind neutrino cooling)

3. The iron core is the final stage of star burning. The iron is inert in nature and the atoms of the iron is so tightly bound and the energy cannot be extracted by fusion. Iron can fuse but it absorbs energy from the sorroundings and the temperature drops by formation of more neutrons and neutrinos

4. inert core with iron cannot further produce energy. but it produces more neutrons and neutrinos by absorbing heat energy. As a result of the sudden loss in energy reduces pressure and the outer layers of star falls into the core with high velocities (less than the velocity of light). The core is having higher density of neutrons which are rigid and massive and incompressible. sow hen the outer layer collapses to the core it gets rebounded at higher velocity( bouncing back ) due to the momentum transfer from the core. as a result of the collison/impact a shock wave is generated inside the core and transferred from inside to the outer stellar surface and hits the surface causing explosion of the star. The exploded star is called as supernova. The energy released out of the explosion is emitted as light and heat energy. the light intensity is so high and the star shines with much brightness for few days

5. The r-process is a nucleo synthesis process that occurs in core collapse supernovae. it produces half of the neutron-rich atomic nuclei heavier than iron.

The term NSE refers to the nuclear statistical Equilibrium in the core supernovae. in this stage the core mainly contains nucleons and alpha particles. much of the iron synthesised in the core of the collapsed supernova is due to the alpha particle freeze out. after the NSE has broken down there remains a large cluster of nuclei from carbon through iron which follows a quasi statistical equilibrium.(QSE)

phase Temperature Required mean density time (years) products Hydrogen burning 4 x 107 degrees K 5 gm per cubic cm 7,000,000 years--- Helium Helium burning 2 x 108 degrees K 700 gm per cubic cm 700,000 years-- oxygen , carbon Carbon burning 6 x 108 degrees K 200,000 gm per cubic cm 600 years oxygen,neon,magnesium Neon burning 1.2 x 109 degrees K 4 million gm per cubic cm 1 year --- oxygen, magnesium Oxygen burning 1.5 x 109 degrees K 10 million gm per cubic cm 6 months-- silicon , sulfur Silicon burning 2.7 x 109 degrees K 30 million gm per cubic cm

1 day nickel 56, Iron

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