What Is a Neutron Star ?

Neutron stars are only a few kilometers in diameter but as massive as stars.

Stars exist because the mass of millions of billions of trillions of tons of hot plasma are being pulled inwards by gravity, while fusion releases energy, which pushes against gravity. Medium stars like our sun eventually turn into white dwarfs

But in stars many times the mass of our sun,things get interesting when the helium is exhausted. It is important to note that not all massive stars follow the same evolutionary path. Though the nuclear burning proceeds in much the same sequence, the effect they have on the star’s hydrostatic equilibrium depends sensitively on the stars mass (see for example Figure 2.1 in Lisakov 2018 below). The exact sequence and extent of radial growth, mass loss, and core contraction, and the number of these phases will be largely determined by the initial mass of the star and the stellar models used to calculate their evolution. 

Iron is nuclear ash, it has no energy to give and cannot be fused.An iron ball the size of the earth is squeezed into a ball of pure nuclear matter the size of a city. But not just the core,the whole star implodes, gravity pulling the outer layers in at 25% the speed of light. This is what we call a supernova. Matter infalling onto a proto-neutron star in a core collapse supernova is falling in at approximately the escape velocity of a neutron star - for a 1 solar mass, 12 km neutron star this is about 50% the speed of light. However, this is not exact. Not all proto-neutron stars have the same mass and they have not finished contracting, and the infalling matter is turbulent and not necessarily spherically symmetric. Nevertheless, infall velocities are guaranteed to be a fraction of the speed of light

Its mass is around a million times the mass of the Earth, but compressed to an object about 25 kilometers wide! Observed neutron star masses vary between approximately 1 and 2 solar masses, with the most massive known at the time of writing being 2.1 solar masses (Cromartie et al 2019), greater than 700,000 Earth masses. Upper limits may be taken to be greater than this but are now generally taken to be less than 3 solar masses, equivalent to approximately 1 million earth masses.That’s roughly a billion tons, in a space the size of a sugar cube.– A neutron star is unbelievably extreme. Its gravity is the strongest outside black holes. Light is bent around it, meaning you can see the front and parts of the back.Their surfaces reach a million degrees Celsius, compared to a measly 6000° for our sun. Neutron stars in many ways are also like planets, with solid crusts over a liquid core. The crust is extremely hard. The outermost layers are made of iron leftover.

Protons and neutrons rearrange, making long cylinders or sheets, which physicists call ‘nuclear pasta. Lumps of pasta inside a neutron star can even make mountains, at most a few centimeters high, but many times as massive as the Himalayas.We’re not really sure what the properties of matter in the core are. Protons and neutrons might dissolve into an ocean of a so called ‘quark gluon plasma Some of those quarks might turn into ‘strange quarks,’ making a sort of ‘strange matter’.

When neutron stars first collapse,they begin to spin very very fast.These radio pulsars are the best known type of neutron star, about 2,000 are known in the Milky Way .These magnetic fields are the strongest in the universe, a quadrillion times stronger than earth’s after they are born.Neutron stars can can crash into and kill each other.Only very recently we learned that this is probably the origin of most of the heavy elements in the universe, like gold, uranium and platinum and dozens more.Only very recently we learned that this is probably the origin of most of the heavy elements in the universe, like gold, uranium and platinum and dozens more.