What is a pulsar?

The pulsars are neutron stars that are observed in the form intermittent or pulsating. They emit radiation constantly but are seen at regular intervals due to the star's spin, similar to what happens with maritime lighthouses.

In this article we will learn how pulsars are formed, why they emit radiation intermittently, and what their main characteristics are.

What is a pulsar?

A press is a type of neutron star very small and dense that rotates at high speed. Pulsars have a very intense magnetic field that causes the radiation emitted by the star concentrated along electromagnetic poles.

When rotating, this radiation beam is received by the observer intermittently as a pulsation, hence the name of these stars. An easy to understand example is to resemble a pulsar star and a maritime lighthouse, in both cases the radiation is emitted along an axis that, when rotating, is seen in a pulsating way.

The first pulsar was detected in 1967 by Jocelyn Bell Y Antony Hewish in the form of radio emissions that came from space at regular and exact intervals. At some point they came to think that they had contacted an extraterrestrial civilization.

Although Jocelyn Bell was the first to detect the radio emission, it was Antony Hewish who won the Nobel Prize in Physics for the discovery and theoretical explanation of the phenomenon in 1974.

Today more than 600 pulsars are known, the most famous being the Crab Nebula pulsar, named PSR0531+121. They should not be confused that the pulsating variable stars.

characteristics of pulsars

pulsar sail
Pulsar candle. Image from the Chandra X-ray telescope

In a simple way, pulsars are rotating neutron stars. The neutron star is one of the possible states after the death of a star of great mass that, after exploding as supernovacollapses its center with such gravity that the protons and electrons of the atoms unite to form neutrons, hence the name of neutron star.

A neutron star has three fundamental characteristics: small size, high mass, and high spin rate.

The size of neutron stars is of the order of 10km radius (20 km in diameter). It is a really small star in size but its mass is about 1.4 times the mass of the Sun.

With this mass and this size, the density of a pulsar is enormous, so much so that if we convert it to terrestrial data it would be equivalent to a teaspoon of dessert weighing a billion tons. And if the density is huge, the associated gravitational force is equally large: 2 x 10eleven times Earth's gravity.

The movement of neutron stars is very fast, being able to complete from hundreds to thousands of revolutions per second. reaching speeds of up to 70,000 km/s. This extreme speed together with the very high density make the electrons that remain on the surface rotate around the nucleus at very high speeds, creating a very intense electromagnetic field.

When particles, such as gases and cosmic dust, approach the neutron star, they undergo a great acceleration due to the effect of high gravity and the electromagnetic field directs them towards the poles where they converge, generating high activity that triggers the emission of diverse electromagnetic radiation, from radiation in the range of radio waves to X-rays and gamma rays.

pulsating emission

Diagram of a pulsar
Diagram of a pulsar

As you can see in the attached images, the axis of rotation of a neutron star and electromagnetic poles do not match. As both axes do not coincide and rotate, the emitted radiation is received in the form of periodic pulses, thus becoming a pulsar.

For example, if we observe the star from Earth, we will receive radiation every time the electromagnetic pole is directed towards the Earth and the electromagnetic beam is launched towards us, which occurs regularly depending on the spin period of the star. This regularity is very exact and constant.

If the axis of rotation and the electromagnetic poles of the neutron star coincided, the observer would receive the beam continuously. But since they do not coincide, the emission beam does not always point towards the Earth or the position of any other observer.

It may also happen that emission from a neutron star is never received, among the possible causes may be that the emission beam never coincides with an observable direction from Earth.

In these cases, it cannot be detected as a pulsar and can be confused with a black hole, having to apply other techniques to differentiate them, often the calculation of the mass being enough data to differentiate both (remember that the neutron star has 1.4 times the mass of the Sun while a black hole is much more massive).

planets around pulsars

The presence of planets revolving around pulsars was unthinkable. But surprisingly, groups of planets orbiting around pulsars have been observed.

The first of these observations was on the pulsar named PSR B1257+12, which has three planets in a nearly circular orbit around it.

The planet that orbits around a pulsar star is known as pulsar planet.

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