Question B4 a) Sketch a graph of the present day abundances of the elements. List the key features of your graph. [5 marks] b) During Big Bang Nucleosynthesis neutrinos freeze out at t≈1s, and Helium production begins around t≈300 s. Give a discussion of the physical processes during this time, and show that the mass fraction of 4He to Hydrogen is approximately 1/4. (You may use the following facts: The temperature of the Universe scales with time as T(t)~ · 1010 K 1º K (15) 12. The number density of a non-relativistic particle of mass m in equilibrium scales as n x e-me²/kBT) [8 marks] c) Explain what is meant by r-process and s-process, and the astrophysical environments in which they take place. Explain, with the aid of a diagram, their importance in the formation of the elements d) [5 marks] Estimate the upper mass of a neutron star in solar mass units. Explain your reasoning, and comment on your answer. (You may assume that the escape velocity for an object mass M and radius R is v = √2GM/R.) [7 marks]

Question B4 a) Sketch a graph of the present day abundances of the elements. List the key features of your graph. [5 marks] b) During Big Bang Nucleosynthesis neutrinos freeze out at t≈1s, and Helium production begins around t≈300 s. Give a discussion of the physical processes during this time, and show that the mass fraction of 4He to Hydrogen is approximately 1/4. (You may use the following facts: The temperature of the Universe scales with time as T(t)~ · 1010 K 1º K (15) 12. The number density of a non-relativistic particle of mass m in equilibrium scales as n x e-me²/kBT) [8 marks] c) Explain what is meant by r-process and s-process, and the astrophysical environments in which they take place. Explain, with the aid of a diagram, their importance in the formation of the elements d) [5 marks] Estimate the upper mass of a neutron star in solar mass units. Explain your reasoning, and comment on your answer. (You may assume that the escape velocity for an object mass M and radius R is v = √2GM/R.) [7 marks]