Neutron Stars and The Mystery of Their Deaths

Neutron stars are extremely violent giant atomic nuclei that are present in masses in the universe. Even though they only have the diameter of a city’s width, about 25 km, their gravitational pull is far more than that of our sun. Neutron stars are not just weird and quirky, they are mysterious as well. They are very different from normal stars. Neutron stars are very fast rotators. The fastest known neutron star spins over 700 times in a second. They are as hot as 1 million degrees celsius and are so dense that the entire human population of nearly 7.8 million would fit in only 1cm³ of a neutron star.

In our galaxy, the milky way, we have over 100 million such stars. These younger siblings of black holes also possess huge gravitational forces like them and just as black holes light bends around a neutron star as well. But how are these neutron stars formed? What is their life cycle and how do they die?

A neutron star is born from a dying massive star. The life cycle of a massive star is a few hundred thousand years. Inside a star, the plasma is constantly getting pulled by its massive gravity. It is because of this gravity that the hydrogen atoms fuse to form helium. This nuclear fusion releases energy that tries to escape out of the star. This is the energy that comes out in the form of heat and light.

Eventually, all the hydrogen inside the star is exhausted and what is left in it is helium. In medium-sized stars like our sun, the star begins to contract and heat up. As a result, the helium gets converted into carbon, oxygen, and nitrogen. After all the helium is exhausted they turn into dwarfs. What happens in massive stars though is very different.

Once all the helium ends, and carbon and oxygen are left, the gravitational pull of the star still keeps pulling the star together and as a result of this in a few centuries, the carbon gets converted to neon, which gets converted to oxygen in a year. The oxygen then gets converted to silicon in a few months which further gets converted to iron in a day and finally, the star dies. Iron is nuclear ash and it cannot undergo any more fusion.

Until now the energy of nuclear fission has maintained the size of the star. But now as there is no fission taking place, the star collapses due to its massive gravity and shrinks to become extremely small compared to its original size. Inside the ball of iron which is the core of the star, are electrons and protons. These protons and electrons do not want to be close to each other. It is because of the high kinetic energies that even after being oppositely charged these particles can come close but not stick to each other.

The massive gravity of the star forces them to come so close that they fuse to form neutrons. These neutrons are packed as tightly inside the iron ball as in atomic nuclei. The entire star comes closer and eventually explodes. This explosion is called a supernova. It is one of the brightest events in the universe. What is left from a supernova is a neutron star.

Neutron star- Inside and Outside

Although these giant atomic nuclei are stars, they are also like planets in many ways. They have a solid crust over a molten core. Their outermost layers are made up of iron left over from the supernova squeezed together in a crystal lattice with a sea of electrons flowing through them.

As we go deeper and deeper into the core of the star the no. of protons constantly decreases as most of them join to form neutrons. Deep inside the core of the star, the gravity is so intense that the neutrons begin to touch. As a result, the protons and electrons rearrange to form first, long strips(like Lazania) and then long chains(like Spaghetti) referred to by scientists as nuclear pasta. 

Because of its nuclear density, this might be the hardest substance in the universe. Lumps of nuclear pasta form mountains on the crust of the neutron star that is often as tall as the Himalayas. At the time of their birth, the neutron stars spin very fast and produce magnetic fields that are the strongest in the universe. It is because of these magnetic fields that these stars are referred to as Magnetars. 

Neutron stars rotate very fast. This is because the star that was earlier very huge has now shrunk into very small size while its angular momentum remains conserved. As a result, the neutron star rotates very fast as compared to its parent star. The neutron stars constantly keep emitting electromagnetic and gravitational waves because of which it loses its angular momentum and slows down.

The reason it emits these rays is because of its high magnetic field. Because of its field, it creates vortexes that release rays from the poles. Since the poles keep changing their position, the phenomenon appears like a lighthouse from a distance. It was because of these flashes recorded by astrophysicists Jocelyn Bell in 1967, that we first discovered neutron stars.

Death of Neutron stars-birth of new elements

Most neutron stars in space exist in pairs with another neutron star. Eventually, their orbits decay and they fall into each other. Leading to a kilonova. In a kilonova, gravitational waves are sent through space and time like ripples from a stone thrown into a calm lake. Gamma rays and x-rays are also emitted in the same process.

Because of the kilonova, most of the matter inside the neutron star is out-split and for a moment heavy nuclei are made again. These nuclei are not formed because of nuclear fusion but it is because of heavy neutron-rich matter reassembling after falling apart. This is probably the origin of most of the heavy elements in the universe like gold, uranium, silver, etc. It is because of the death of neutron stars that perhaps our solar system exists.

Millions of years after the death of neutron stars, the matter from neutron stars is pulled together by gravity and solar systems such as ours are formed. Also, many stars are reborn from the matter of a dead neutron star. The phenomenon of kilonova was first predicted in Einstein’s theory of relativity. It was later verified in 2017 when gravitational wave observatories Ligo and Virgo observed a neutron star collision. This incident later became the most studied event in all of astrophysics.

Many other neutron stars end up losing their energies through the emission of gravity and electromagnetic waves. There have also been cases where a neutron star that co-orbits another lighter star, feeds on that star, absorbing all its mass and energy before it collapses into a black hole.

Conclusion:

Even though today a lot is known about these dense pulsating spinning magnets yet it seems like it’s not even half the book read. Ligo and Virgo are being upgraded to record the demise of neutron stars that are far from the Earth in the infinite universe. The end of these stars is considered to be the origin of solar systems like ours.

But the proof is yet to be found. Neutron stars seem to attract everyone’s attention; they are examples of how perfect the universe actually is. They show how things the universe generates from one another. Perhaps the universe is a cycle of death and regeneration that we humans have a lot to explore about.