In: Physics
Suppose a star the size of our Sun, but with mass 5.0 times as great, were rotating at a speed of 1.0 revolution every 18 days. If it were to undergo gravitational collapse to a neutron star of radius 14 km , losing three-quarters of its mass in the process, what would its rotation speed be? Assume also that the thrown- off mass carries off either
part a. no angular momentum
part b. its proportional share three-quarters of the initial angular momentum
The mas of the star is
The radius of the star is
The moment of inertia of the star is
The period of revolution is
So, the angular speed of the star is
So, the initial angular momentum of the star is
PART A: When no momentum is lost
The radius of the collapsed star is
The mass of the collapsed star is
The moment of inertia of the collapsed star is
The angular momentum of the collapsed star is
The conservation of angular momentum gives us
So, the new rotational speed of the collapsed star is 39887 rad/s.
PART B: When three-quarters of the momentum is lost
The radius of the collapsed star is
The mass of the collapsed star is
The moment of inertia of the collapsed star is
The angular momentum of the collapsed star is
The three-quarter of the initial angular momentum is lost.
So, the conservation of angular momentum gives us
So, the new rotational speed of the collapsed star is 9972 rad/s.