Neutron Stars


To understand pulsars, we need to understand what a neutron star is. A neutron star is sometimes formed when a star runs out of fuel (hydrogen), and collapses. There are 3 things that can happen when a star dies- it can collapse into a white dwarf, a neutron star, or a black hole. The mass of the star determines what the star leaves behind.

So the stars that eventually become neutron stars were once huge stars, with a mass 4-8 times bigger than the Sun. When these stars run out of hydrogen to burn, they undergo a supernova explosion. They throw off their outer layers, whilst the core collapses under gravity. It is this core which becomes the neutron star. Unsurprisingly, the star is made of neutrons, which are formed when the protons and electrons are pushed together so hard that they combine into neutrons:

 

The result is a very dense star, made of neutrons packed incredibly close together. To get an idea of how dense this really is- one teaspoon of neutron star weighs about the same as a mountain on Earth, or 900 Great Pyramids of Egypt! A neutron star is much smaller than a normal star, typical neutron star diameters are only a few tens of kilometers, roughly the same diameter as a small city.

Neutron stars have very strong gravitational fields, and also some of the strongest magnetic fields in our Universe. In fact, a neutron star can wipe a credit card at 100 000 miles!

Advanced: How do neutron stars have magnetic fields if they are just made of neutrons? This is because the star had a magnetic field before it collapsed. This magnetic field must be conserved, so it is present in the neutron star. Because the neutron star is so much smaller than the original star, and yet has the same amount of magnetic flux, the strength of the neutron star’s magnetic field is huge!

So a pulsar is a spinning neutron star. Pulsars give out intense pulses of radiation- how does this happen?

Next page: How do Pulsars send out Pulses of Radiation?

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