What would happen if a star with over 10 to 25 times the mass of our Sun goes supernova? There are two probabilities due to the resulting supernova explosion; one would lead to forming a black hole, and the other leading to the formation of Neutron stars. With the most powerful gravitational field and magnetic force, Neutron stars are spinning balls of collapsed stars that illuminate the night sky. Astronomers have discovered nearly 2000 Neutron stars in the milky way and theorize that there could be over 1 million in our neighbouring galaxies.
How is a Neutron Star Formed?
In our universe, new stars are formed from the remnants of collapsed stars. The same is true in the case of a Neutron star. Before understanding how Neutron stars were formed, we need to know a little about stars and the cause of a gravitational collapse. Stars comprise millions and billions of hot plasma that is being pushed into the core due to gravity that nuclei fuse. Hydrogen fuses into Helium, thereby releasing energy that pushes against gravity and tries to escape. Stars are quite stable as long as this balance exists. However, over a few billion years, this Helium will get depleted and result in the star growing into a red giant. Medium-sized stars like our Sun will burn Helium into Carbon and Oxygen during the end of their life, swelling into a red giant. These medium-sized stars will turn into white dwarfs.
Gravitational Collapse Resulting in a Supernova
However, for stars that are 10 to 25 times the mass of our Sun, the internal reaction would be far different once the Helium gets exhausted. The balance of pressure and radiation collapses, and gravity will squeeze the star tighter, and the core would burn hotter and faster, resulting in the star swelling hundreds of times. At this stage, heavier elements will begin to fuse; carbon burns to neon in a few centuries. Neon burns to Oxygen in a few months, Oxygen burns to Silicon in months, and Silicon burns to Iron. This Iron ball is nuclear ash with no energy to give and therefore cannot be fused. Without the outward pressure from fusion, the core gets crushed due to the enormous weight around it.
Due to the collapsing weight of the star, the electrons and protons fuse into neutrons and further gets squeezed together. This is known as a gradual gravitational collapse. Here, an iron ball the size of the Earth gets crushed into a small ball the size of a city. This will result in the whole star imploding with gravity, pulling the outer layers of the star at 25% the speed of light. This implosion bounces off the iron core, producing a massive shockwave with the remnants of the star spewed into space. This is known as a supernova explosion, which is so bright that it could outshine galaxies. After the explosion, what remains is a Neutron star with the mass of over a million Earths but compressed to an object which is nearly 25 km wide.
The Nature of a Neutron Star
A Neutron Star’s gravity is the second strongest in the universe, first to black holes. If a Neutron star gets denser, it could even become a black hole. Even light gets bent around it, so you can only see the front and parts of the back. They are massively hot as they burn at a million-degree Celsius. Just like planets, Neutron stars also comprise an atmosphere, crust, and core. The crust is very hard as the outermost layers comprise iron leftover from the supernova explosion. On the crust, there are enormous nuclei with millions of protons and neutrons shaped like spaghetti. Physicists call this nuclear pasta which is known to be one of the densest and strongest materials in the universe. Nobody knows what the core of a neutron star might comprise due to its dense nature. Physicists theorize that protons and neutrons might dissolve into an ocean of quarks known as the Quark-Gluon plasma.
Celestial Ballerinas
Have you ever seen a ballerina spinning by pulling her arms in? When Neutron stars collapse, they begin spinning very fast, several times per second. PSR J1748-2446ad is one of the fastest spinning neutron stars in our universe, spinning at 716 times a second, which is nearly 25% the speed of light.
The spin of Neutron stars creates radio pulses that can be detected. These are known as radio pulsars, which are the best-known type of neutron stars. These fast-spinning celestial ballerinas are known as magnetars until they calm down. Magnetars are 1000 times stronger than regular neutron stars, with a magnetic field that is 100 million times stronger than the most powerful man-made magnets.
The Collision of Two Neutron Stars Forms a Black Hole
The best types of Neutron stars are friends with other neutron stars. While radiating energy like gravitational waves and ripples in space-time, two Neutron stars would collide as their orbits decay. Their collision would result in both stars getting destroyed in a killonova explosion, forming a black hole. The remnants of the explosion and debris of a killonova explosion will mix back into the galaxy. Some of them end up in a cloud that gravity pulls together, leading to the formation of stars and planets. This process would repeat as a cycle.
Even our solar system is the product of the remains of collapsed Neutron stars. In fact, all the elements in our technological world are built out of the elements Neutron stars made billions of years ago.
Space Age 