February 27, 2020 0

What Are Neutron Stars?

What Are Neutron Stars?

Hey Crazies
As we saw in the last video, white dwarfs are pretty awesome. They’re the left over core of a low-mass
star like our Sun shrunk to the size of a planet or moon. But we can get even smaller than those white
dwarfs. White dwarves, white dwarves, white dwarves The next group of stellar corpses is the neutron stars. Let’s do this! As you can see from this chart, the original
star that makes a neutron star needs to have at least 8x the mass of our Sun. Anything less and it’ll only make a white
dwarf. Anything more than 20 and it becomes a black
hole. Neutron stars are the sweat spot in-between. How come an 8 solar-mass star doesn’t make
an 8 solar-mass neutron star? Because the whole star doesn’t become the
neutron star. Just its core. A star’s core is where the fusion is happening,
but that core is surrounded by several other layers that are just hot. Those outer layers are where you’ll find
the majority of the star’s mass, but those layers get blasted away during the star’s
death throes. Only the core is left behind to collapse into
a stellar corpse. So an 8 solar-mass star only makes a 1.4 solar-mass
corpse and a 20 solar-mass star only makes a 3 solar-mass corpse. A Neutron Star is exactly what it sounds like:
a star made of neutrons. You know those little particles you usually
find in an atomic nucleus. Except the whole star is made of neutrons. Well, almost. How is that even possible?! Because gravity’s a thing!! That left-over stellar core is heavy, so it
collapses under its own gravity, which speeds up the particles inside. Mostly the electrons. The faster they’re going, the more kinetic
energy they have. If the core collapses enough, the total energy
of the electrons will make up for the mass difference between the protons and neutrons. At that point, the protons will react with
the electrons and become neutrons. This inverse beta decay, as it’s called,
happens through most of the collapsing core. After the star’s millions or billions of
years of life, this last process is very violent and very fast. In a matter of hours-to-days, the extreme
temperatures release gamma-rays that smash larger nuclei like Iron into smaller nuclei
like Helium. The inverse beta decay turns protons into
neutrons releasing a flood of neutrinos into space. That core will continue to collapse until
something stops it. Cue the Pauli Exclusion Principle!!! That principle doesn’t just apply to electrons. It applies to all fermions. Neutrons are also spin-1/2 particles. They’re fermions too. But because they’re neutral, they can get
a lot closer together. They reach densities comparable to atomic
nuclei before they stop collapsing. Unlike the white dwarf, which is the size of a planet or moon, a neutron star would
be the size of a small city. Is it true that a teaspoon would weigh as
much as a mountain?! Uh not exactly. Ok, so a teaspoon (prop) of neutron star matter,
also known as neutronium, would have the mass of a small mountain. But mass and weight are not the same thing. On the surface of a neutron star, it’s going
to weigh a lot more than a mountain because a neutron star’s gravity is much stronger than
Earth’s. A trillion times stronger! What if we scooped it up and brought it to
Earth? It would explode. The only thing keeping that neutronium stable
is the gravity of the neutron star. You won’t get that teaspoon very far before
most of it decayed back into protons and electrons releasing unimaginable amounts of radiation
very quickly. You Dead! Plus, if you’re scooping that matter from
the outside of the neutron star you’re probably not getting just neutrons. The electrons on the outside of the collapse
weren’t moving fast enough to make more neutrons, so that stuff still behaves more
like white dwarf matter. This also explains how it’s possible for
neutron stars to make magnetic fields. Remember, magnetic fields require charge. Neutral things can’t make them. Thankfully, neutron stars have some protons
and electrons left over on the outer edges. Those particles are the source of a neutron
star’s strong magnetic field. But that field doesn’t necessarily line
up with the star’s rotation. At the north and south poles, you’ll find
outward jets of charged particles and, since those charges are accelerated, they produce
light that beams into space. Light that could be anywhere on the spectrum
from radio to gamma-rays. This creates a kind of lighthouse effect, and
if things line up just right, we can receive a regular pulse here on Earth. If that’s the case, we call it a “Pulsar”
which is just short for pulsing star and these things spin fast fast!!!! So the pulses are more like this or even faster. This used to be the only way we could discover
them, but, now with LIGO, we can detect more of them by their gravitational waves. Especially, when they hit each other like
this! Ow! The BEEP was that for? On top of that, because of gravitational warping
neutron stars would look really weird up close. You could actually see part of its back when
looking at the front. These things are weird. So, got any other questions about neutron
stars? Ask in the comments. Thanks for liking and sharing this video
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