) In class, we will describe classical novae as the explosive thermonuclear burn
ID: 1450160 • Letter: #
Question
) In class, we will describe classical novae as the explosive thermonuclear burning of an accreted H layer on the surface of a white star in a binary system. Consider a 1.4 M, R = R white dwarf. (From 2015 exam) a. (5 pts.) What is the gravitational potential energy released when a proton accretes onto the surface of a white dwarf? (Express your answer in MeV.) b. (5 pts.) How much energy is released per proton from burning H to He? (Express you answer in MeV.) c. (2 pts.) How do these compare and what might you conclude about the possibility of a nova explosion ejecting material?
Explanation / Answer
a. gravitational potential energy at the surface(V)= GMm/r;
where, m-mass of the proton=1.67 x 10-27 ; M=1.4x 1.989 x 1030 ;r= 6.96 x 108 m
energy released(V)= 4.46 x 10-16 J ={divided by electrons charge} =2790.952 eV= 2.79 x 10-3 MeV
b) mass of helium atom(Mh)= 6.644 x 10-27
mass of a proton-Mp
In fusion helium atom is formed by fusing 4 protons. So form einsteins E=mc2
released energy= (4*Mp- Mh)*c2 = 26.149 MeV
c) Fusion energy is much larger than accretion energy. Since the accretion release of energy is much lower, possibility of ejecting material is very low
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