What Is A Pulsar?

First observed in 1967, some astronomers speculated that pulsating stars could be signals from another civilization. Not until many more were discovered did scientists begin to put the pieces together.

A pulsating star, or pulsar is a highly magnetized, spinning neutron star that emits pulses of electromagnetic radiation along its magnetic axis. Pulsars emit beams in very precise intervals, even some rivaling the accuracy of an atomic clock. They are extremely dense, and have short, regular rotational periods.


A graphic of a pulsar. Image credit: dreamstime

Pulsars mark the infancy period of a neutron star. When a massive star dies in a supernova explosion it leaves behind an ultra-dense remnant known as a neutron star. The neutron star retains most of its angular momentum, forming with a very high rotation speed. The rotational energy of the neutron star excites the magnetic field causing the star to emit beams along its magnetic axis. The magnetic axis and the rotational axis are not necessarily the same (as shown in the image below), and this misalignment is what leads to the “pulsed” appearance.


A graphic showing the misalignment of the magnetic axis and the rotational axis. Image credit: Roy Smits

All neutron stars were pulsars at one point in time – how long they last depends on how fast and how long they can continue to rotate. Over time, as a pulsars rotation slows, the pulsating mechanism is believed to turn off. Observations have shown pulsars to last between 10 million and 100 million years before they slow down enough for the pulse to die, therefore becoming a conventional neutron star.

Pulsars have short, regular rotational periods that produce very precise intervals between pulses, ranging from milliseconds to seconds, depending on how fast the rotation is. In 1982, a pulsar was discovered that completed 38,500 rotations per minute (RPM), with a rotation period of just 1.6 milliseconds. Thus a new class of objects, called millisecond pulsars, had been found.

Although our picture of pulsating stars has become much clearer over the past four decades, Werner Becker of the Max Planck Institute for Extraterrestrial Physics said in 2006, “The theory of how pulsars emit their radiation is still in its infancy, even after nearly forty years of work.”

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