Explain the steps of a core collapse and explosion

Core-collapse

All supernovae are produced via one of two different explosion mechanisms. The thermonuclear explosion of a white dwarf which has been accreting matter from a companion is known as a Type Ia supernova, while the core-collapse of massive stars produce Type II, Type Ib and Type Ic supernovae.

All stars, regardless of mass, progress through the first stages of their lives in a similar way, by converting hydrogen into helium. As the hydrogen is used up, fusion reactions slow down resulting in the release of less energy, and gravity causes the core to contract. This raises the temperature of the core again, generally to the point where helium fusion can begin. Once helium has been used up, the core contracts again, and in low-mass stars this is where the fusion processes end – with the creation of an electron degenerate carbon core.

For massive (>10 solar masses) stars, however, this is not the end. The contraction of the helium core raises the temperature sufficiently so that carbon burning can begin. After the carbon burning stage comes the neon burning, oxygen burning and silicon burning stages, each lasting a shorter period of time than the previous one. The end result of the silicon burning stage is the production of iron, and it is this process which spells the end for the star.

find the surface area of the sphere to the nearest square unit. use a calculator.

a. 254 in.2

b. 64 in.2

c. 127 in.2

d. 1,018 in.2

the doppler effect is used by weather forecasters to measure 

moving clouds