Neutron stars are one of the most extreme things in the universe. They’re like giant atom cores. Kilometers in diameter, unbelievably dense and violent.
But how can something like this even exist?
The life of a star is dominated by two forces being in balance:
1. Its own gravity
2. The radiation pressure of its fusion reaction
In the core of stars, hydrogen is fused into helium. Eventually, the hydrogen in the core is exhausted.
If the star is massive enough, helium is now fused into carbon.
The cores of these massive stars become layered like onions, as heavier and heavier atomic nuclei build up at the center.
Carbon is fused into neon, which leads to oxygen, which leads to silicon.
Eventually, the fusion reaction hits iron, which cannot fuse into another element.
When the fusion stops, the radiation pressure drops rapidly.
The star is no longer in balance, and if its core mass exceeds about 1.4 solar masses, a catastrophic collapse takes place.
The outer part of the core reaches velocities of up to 70,000 km per second as it collapses towards the center of the star. Now, only the fundamental forces inside an atom are left to fight the gravitational collapse. The quantum-mechanical repulsion of electrons is overcome. Electrons and protons then fuse into neutrons packed as densely as an atomic nucleus.
The outer layers of the star are catapulted into space in a violent supernova explosion.
So, now we have a neutron star!
Its mass is between 1 and 3 Suns, but compressed to an object about 25 kilometers wide! And 500,000 times the mass of Earth, in this tiny ball that’s roughly the diameter of Manhattan.
It’s so dense that one cubic centimeter of neutron star contains the same mass as an iron cube 700 meters across. That’s roughly 1 billion tons, as massive as Mount Everest, in a space the size of a sugar cube.
Neutron star gravity is so impressive that you might have to talk to a physics expert to wrap your mind around it!
If you were to drop an object from 1 meter over the surface, it would hit the star in one microsecond and accelerate up to 7.2 million km per hour. The surface is superflat, with irregularities of 5 millimeters maximum, with a superthin atmosphere of hot plasma. The surface temperature is about 1 million kelvin, compared to 5,800 kelvin for our Sun.
Let’s look inside the neutron star! The crust is extremely hard and is most likely made of an iron atom nuclei lattice with a sea of electrons flowing through them. The closer we get to the core, the more neutrons and the fewer protons we see until there’s just an incredibly dense soup of indistinguishable neutrons.
The cores of neutron stars are very, very weird.
We are not sure what their properties are, but our closest guess is that the cores are composed of superfluid neutron degenerate matter or some kind of ultradense quark matter called quark-gluon plasma. That does not make any sense in the traditional way and can only exist in this ultra-extreme environment.
In many ways, a neutron star is similar to a giant atom core. The most important difference is that atom cores are held together by strong interaction in quantum theory and neutron stars are held together by gravity.
As if all this wasn’t extreme enough, let’s take a look at a few other properties. As Stephen Hawking would verify if he were still alive, Neutron stars spin very, very fast, young ones several times per second. And if there’s a poor star nearby to feed the neutron star, it can rotate up to several hundred times per second. Like the object PSRJ1748-2446ad. It spins at approximately 252 million km/h. This is so fast that the star has a rather strange shape. We call these objects pulsars, because they emit a strong radio signal. And the magnetic field of a neutron star is roughly 8 trillion times stronger than the magnetic field of Earth. This is so strong that atoms get bent when they enter its influence!
Okay, I think we got the point across. Neutron stars are some of the most extreme, but also some of the coolest objects in the universe. Hopefully, we will one day send spaceships to learn more about them and take some neat pictures! But we shouldn’t get too close!