pulsar

History

Pulsars were discovered in 1967 by graduate student Jocelyn Bell, who noticed regular signals on a radio telescope. At first, they were even thought to be signals from aliens! Later, it was realized they were rapidly spinning neutron stars.

How it works

A neutron star, the size of a city, is compressed to the limit and retains its rotation, like a figure skater pulling in her arms. Its magnetic field twists and generates radiation that emerges from the poles in narrow beams. If Earth lies in the path of such a beam, we see a pulsation.

History

Pulsars were discovered in 1967 by graduate student Jocelyn Bell, who noticed regular signals on a radio telescope. At first, they were even thought to be signals from aliens! Later, it was realized they were rapidly spinning neutron stars.

How it works

A neutron star, the size of a city, is compressed to the limit and retains its rotation, like a figure skater pulling in her arms. Its magnetic field twists and generates radiation that emerges from the poles in narrow beams. If Earth lies in the path of such a beam, we see a pulsation.

History

The idea of neutron stars was proposed by Fritz Zwicky and Walter Baade in 1934, but the discovery of pulsars occurred in 1967 by Jocelyn Bell Burnell under the supervision of Antony Hewish. At first, the signals were named LGM-1 (little green men). In 1968, Franco Pacini and Thomas Gold independently linked pulsars to rotating neutron stars. Since then, thousands of pulsars have been discovered, including binary ones, which allowed testing of the theory of gravity. Fritz Zwicky was a pioneer in predicting neutron stars.

How it works

A pulsar works due to conservation of angular momentum. During collapse, the core shrinks to a radius of ~10 km, increasing the rotation speed. The magnetic field intensifies, and radiation is generated in the polar caps, where charged particles are accelerated along field lines, producing coherent radiation. Precession and spin-down are described by equations of electrodynamics and general relativity, for instance, energy loss to gravitational waves for rapidly rotating asymmetric pulsars.

Open problems & fun facts

The exact mechanism of coherent radiation generation is unknown.; Why do pulsars exhibit glitches (rotation irregularities)?; Can pulsars be used to detect low-frequency gravitational waves?; What is the structure of matter in the core of a neutron star?

💡 The fastest pulsar spins 716 times per second — faster than a kitchen blender!