The average energy of particles in the early phase of the universe, when it was very
hot, was approximately 10 GeV. Calculate the corresponding temperature.
The mass and radius of a neutron star is 2MΘ and 15 km, respectively. Calculate the
value of gravitational red shift for light of wavelength 6000 Å at a distance of 2 m
from its surface.
Write down the condition under which a large molecular cloud collapses to give rise
to new stars. Calculate the time of free fall of an HI cloud of density 106
particles/m