How pulsars form

The universe is filled with strange and exotic objects. One that is quite fascinating is a pulsar, for many reasons. Once a person has a general idea of what a pulsar is, it is natural that they might want to know how they are created.

What a pulsar is

The name “pulsar” is short for pulsating star. This part is basic but that is what the star does. The National Aeronautics and Space Administration’s Goddard Spaceflight Center has a more technical definition: “A pulsar is a neutron star that emits beams of radiation that sweep through Earth’s line of sight.” In other words, it is an extremely dense star that emits pulses of radiation that can then be detected on the Earth, hence the name.

Neutron star

Since a pulsar is a neutron star, it is good to have an idea of what a neutron star is, in order to understand how pulsars are created. Neutron stars are incredibly densely packed stars formed when massive stars die. Without getting too technical, the matter in the star’s core collapses in on itself. Electrons, with a negative electrical charge, are forced together with protons, which have a positive electrical charge. The result is a neutron, which has no charge.

For this to happen, the orbiting electrons are forced into the protons in the nucleus of the atoms by the forces of a gigantic explosion and the subsequent stellar collapse. Since normal atoms consist of mostly space, the density of what is left of the atoms, and of the star itself, grows enormously as the star becomes compressed. Put in another way, also by NASA, a typical neutron star has a radius of about five miles, yet it has just less than one and a half times the mass of Earth’s sun.

To add perspective, the sun has a diameter of almost 430,000 miles. A teaspoon full of neutron star material would weigh millions of tons.


Stars rotate, just as the earth does. As a star collapses, as in the case of a neutron star, the rotation increases. This is the same sort of thing that happens when a spinning ice skater draws in his or her arms and legs, though on a vastly larger scale. A neutron star can revolve many times each second, despite being miles in diameter. 


As stated by Goddard, though paraphrased, “The ‘pulses’ of high-energy rotation of the neutron star causes the beam of radiation generated within the magnetic field to sweep in and out of our line of sight with a regular period, somewhat like the beam of light from a lighthouse. The stream of light is, in reality, continuous, but to a distant observer, it seems to wink on and off at regular intervals.”

The creation and cause

All of this adds up to the creation of a pulsar; it starts with a supernova explosion, forming a neutron star. If the magnetic field is not inline with the rotation of the star and if the tilt swings toward the earth, the energy is seen as pulses of energy. 

Many pulsars are known and there is little doubt that there are many more that haven’t been discovered yet. One of those that are known, however, is the Crab Pulsar, within the Crab Nebula, which spins about 30 times a second. The supernova explosion that caused it was actually documented in the year 1054 by both Chinese and Arabic astronomers. This pulsar is important because it gave the hints regarding the connection between pulsars and supernovas. It was the “smoking gun,” so to speak, that allowed scientists to figure out how pulsars were created.