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.

Its own gravity and 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/s,

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,

and electrons and protons
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 pretty impressive too!

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/h.

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

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 such an
ultraextreme 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
and neutron stars by gravity.

As if all this wasn’t extreme enough,

let’s take a look at
a few other properties.

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.

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!