Answer to Question #170598 in Astronomy | Astrophysics for Jashanpreet Singh

Question

Radio telescopes are an essential tool for modern astrophysics. They played a crucial role in

discovering a fascinating astronomical object: Pulsars - highly compact objects that periodically

emit radiation. Pulsars are still an active part of astrophysical research.

Explain how pulsars are formed and the causes for their pulsating behaviour.

Answer 1

Pulsar is one of the final stages of stellar evolution. It is a neutron star or, rarely, white dwarf with large magnetic field and very small period of rotation.

We see the emission from two narrow beams at the magnetic poles. Due to rotation of the star we don't see the poles all the time, but they rotate and become visible only periodically. It is so because of difference between the rotation and magnetic axes. Therefore, the emission of the pulsar takes form of small periodic impulses.

The large magnetic fields and small periods of rotation are caused by the collapse of massive star. The radius of object is significantly decreased, but the total angular and magnetic moments are retained, so the angular velocity and the strength of magnetic field are greatly enhanced. And the period becomes very small, less than a second for some kinds of pulsars.

For example, the periods of rotation of millisecond pulsars are only thousandth of second, and magnetic fields of magnetars are $10^9 - 10^{11} \, \text{T}.$

Due to their stability, pulsars may be treated as a kind of clock, however, they are not as stable as atomic clocks.