5: NEUTRON STARS AND PULSARS

Question 1

Define neutron star

Answer 1

A compact object consisting almost entirely of neutrons and supported by degenerate neutron pressure

Question 2

Define pulsars

Answer 2

Rapidly rotating highly magnetised neutron stars

Question 3

What can you determine from a neutron star’s orbit?

Answer 3

Their mass

Question 4

What is the reason for some NS having higher masses than expected?

Answer 4

Accreting material from companion

Question 5

What does the short period of pulsars imply? Why?

Answer 5

1. A compact object
2. Causality suggests the period of a variation can’t be shorter than the light crossing time of the object

Question 6

In which frequency is pulsed emission detected?

Answer 6

Most prominently in the radio but sometimes across the whole EM spectrum.

Question 7

Emission mechanism of a pulsar…
- Why is curvature radiation emitted?
- What happens near the pulsar as well as further away from the pulsar?
- When rotation exceeds c, what happens to the field lines and plasma?
- What happens when a beam passes across the observer?

Answer 7

1. Because charged particles stream away from pulsar on curved magnetic field lines.
2. Close to the pulsar, the field lines and surrounding plasma rotate with the pulsar but beyond some radius, the rotation would exceed c.
3. Field lines passing this radius can’t close and plasma can stream away along them emitting radiation along the rotation axis.
4. When this beam passes across the observer, a pulse of emission is seen.