Neutron Stars
Neutron stars are one of the most extreme objects in the universe besides black holes, they are very small compared to other celestial objects and have the most powerful magnetic fields in the universe.
Formation
To understand what a neutron star is, we can start by understanding its formation. Neutron stars form from the death of stars, but not any kind of star, for example, our sun won’t turn into a neutron star once it dies, it will turn into a white dwarf which is another type of celestial body. The star must be massive enough to be able to form a neutron star.
Stars are made of hot plasma that is constantly being pulled inward by the force of gravity. The pressure caused by the immense force is so much that it causes nuclei to fuse, which converts hydrogen atoms into helium (this is nuclear fusion!). This releases energy that pushes against the force of gravity and maintains a balance that makes the star stable.
Everything is fine until hydrogen runs out, for medium-size stars like our sun, helium begins to be used as fuel and burns into carbon and oxygen, and the star eventually becomes a white dwarf. However, the situation changes when we’re
talking about bigger more massive stars. As soon as helium is exhausted, gravity begins to win the battle against the energy released from fusion, which causes the star to get squeezed and hence makes the core burn hotter than before. The outer layers of the star begin to swell by hundreds of times, which makes it possible for the star to fuse heavier elements.
Carbon burns to Neon, Neon to Oxygen, Oxygen to Silicon, and Silicon to Iron.
Iron cannot be used to fuse, so the fusion completely stops and gravity wins completely. The core is now getting crushed by the immense weight of the star, so much so that electrons and protons fuse and form neutrons. The iron core from the star has been squeezed from being about the size of Earth to now being only about the size of a city.
Remember all the outer layers form the star? Well since gravity completely took over, all of these layers are now pulled in at 25% of the speed of light. Everything falls into the iron core, which bounces off and explodes, sending the rest of the star into space. The star has gone supernova!
Neutron Stars
What remains now is a neutron star! This is how neutron stars form, and their properties are extremely strange. First of all, although they are only about the size of cities, they contain around 1,000,000 times the mass of Earth. To give you an idea of how much that actually is, it’s as if you had a billion tons in only one single sugar cube.
Not only are they extremely dense, but neutron stars also have the second-strongest gravitational force in the entire universe, the number one being black holes. Besides this, the temperature of our sun is nothing compared to the temperature of a neutron star. Our sun is about 6,000 degrees Celsius, while a neutron star is about 1,000,000 degrees Celsius. The difference here is astronomical (literally).
Pulsars
There’s also another category of neutron stars, which we call pulsars. Pulsars occur when a neutron star first collapses, which at the moment begins to spin extremely fast. So fast actually that they can spin many times per second, just imagine how fast that is. When they are spinning like this, they also create pulses because of their magnetic fields, which emits a beam of radio waves every time they spin. These are pulsars and are the most known type of neutron star. Pulsars have the strongest magnetic fields of any other celestial object in the entire universe, and during their most active times they are called ‘magnetars’.
Neutron Star Merger
What happens when a neutron star collides with another neutron star? They start rotating against each other, which causes gravitational waves (will talk about this eventually as well!). When they collide, they cause a kilonova explosion, which similarly to a supernova, also sends material flying into space. The key difference is that during a kilonova explosion, heavier elements are made, like gold, uranium, platinum, iridium, and more. After the collision, the two neutron stars will become a black hole!
Bibliography:
Neutron Stars – The Most Extreme Things that are not Black Holes (Kurzgesagt):
What are neutron stars. The cosmic gold mines, explained:
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