Question

C. i. As a star runs out of hydrogen to fuel nuclear fusion in its core, changes within the star usually cause it to leave the main sequence, expanding and cooling as it does so. Would a star with a radius 100 times that of the Sun, but a surface temperature 0.4 times that of the Sun, be more, or less luminous than the Sun? Show and explain your reasoning. You may assume the surface area of a sphere is A=4nra. (Hint: you will need to consider the proportional effect on stellar luminosity of both the change in the surface area and the change in surface temperature of a star, as implied by Equation 4.2 (see Topic 10, Section 4.1.2). It isn't necessary to input actual values.) (6 marks) ii. During a supernova, a neutron star can be formed from the core of the massive star. How is this formed? What else could be formed? (3 marks)

Answer 1

Stellan huminocity L24TR Tt 4 2 Pranknown Inkinam XT Linknown - R Lsum R² To com (100 x0-4 Team Sum € R² Sant To sum = 256 Lumiknor = 256 XL "Sum Lunknown> L sum

$\sigma$ Stephan boltzmann constant.

Neutron stars are something that is part or quantity that is left after the greater part has been used, removed, or destroyed, of giant stars that died in a fiery explosion known as a supernova. When the core of the star has completely burned to iron, energy production stops and the core rapidly collapses, squeezing electrons and protons together to form neutrons and neutrinos. The neutrinos easily escape the contracting core but the neutrons pack closer together until their density is equivalent to that of an atomic nucleus. At this point, the neutrons occupy the smallest space possible and, if the core is less than about 3 solar masses, they exert a pressure which is capable of supporting a star. For masses larger than this, even the pressure of neutrons cannot support the star against gravity and it collapses into a stellar black hole. A star supported by neutron degeneracy pressure is known as a ‘neutron star’.