we've traveled to lots of weird places
on this show from the interiors of black
holes to the time before the big bang
but today i want to take you on a
journey that has got to be to the
weirdest place in the modern universe a
place where matter exists in states
that i bet you've never heard of today
we take a journey to the center of the
neutron star
neutron stars are arguably the strangest
objects in the universe if we don't
count black holes as actual objects and
honestly neutron stars are even weirder
than black holes in some ways
now we've talked about these things
before about how they form from the dead
cores of massive stars left over after
supernova explosions
we've seen how they look from afar
perfect metronomes of flashing light as
these rapidly spinning stars sweep us
with their jets as pulsars
and we've explored strange processes
that occur as a neutron star approaches
becoming a black hole
but what we've never done at least not
properly is to really explore the
insides of these beasts
and it's time we did so because there
we'll find states of matter that exist
nowhere else in the universe
for this journey we're going to need an
unthinkably advanced spacecraft in fact
there is no imaginable technology that
could withstand the conditions that
we're about to experience
so we're relying on the amazing power
of bad science fiction
an indestructium craft to withstand the
radiation and pressure and an
anti-gravitational field to resist the
ridiculous gravitational forces and all
this stuff is going to come in handy as
soon as we approach the neutron star
the first thing we encounter is its
magnetosphere
this is the strongest magnetic field in
the universe
even the weakest neutron star fields are
a billion times stronger than those of
the earth or the sun
this magnetosphere is very different
from the magnetized space around the
earth or the sun it's filled with
electrons and positrons these matter
antimatter pairs are created out of the
extreme energy photons in the magnetic
field
that field then becomes a particle
accelerator with electron currents
flowing one way and positron currents
flowing the other way due to their
opposite electric charges
these and other charged particles end up
being blasted out along the poles of the
magnetic field and their motion in those
jets results in the radiation that we
observe as pulsars when we're nearly
through the magnetosphere we start to
notice that the neutron star's surface
is a little fuzzy
we're seeing the stars atmosphere
similar to the earth's atmosphere this
layer of haze starts out very tenuous
almost a vacuum and then gets denser as
we drop
but the similarities end there
earth's atmosphere is mostly oxygen and
nitrogen in molecular form
pressure increases as you go down so
that at earth's surface the weight of
all that gas on top of your head is
about 200 kilograms but the neutron
star's atmosphere is not made of atoms
rather it's a plasma in which atoms have
been stripped of their electrons or
ionized due to the extreme heat around a
million kelvin for a young neutron star
those nuclei are mostly hydrogen and
helium captured from the nearly empty
space surrounding the star and while
earth's atmosphere is something like 100
kilometers thick depending on how you
define the edge of space the neutron
star's atmosphere is barely a meter
thick with most of the plasma confined
to a thin shell 10 centimeters above the
star surface
now this is due to the insane gravity at
that surface which i'll come back to
once we've landed on the surface our
heads are in the vacuum of space while
our feet are in a foggy plasma with a
density many million times greater than
anything on earth and the gravitational
pull here is something like a hundred
billion g's here we start to encounter
the first truly strange states of matter
see the matter at your feet is not all
that different from the stuff of a white
dwarf the dead core of a lower mass star
like our sun the plasma is crushed so
tight that electrons are on the verge of
overlapping but as we saw in previous
episodes particles of the fermion family
can't occupy the same quantum state the
matter has become what we call
degenerate and electron degeneracy
pressure stops further collapse and
ultimately holds the atmosphere up
having landed on the neutron star we
actually do have a solid surface below
our feet
it appears to be some strange sort of
crystalline material
now that's pretty weird because we
normally think of crystals as lattices
of atoms connected by electron bonds
but the stuff below our feet is still
completely ionized still stripped of its
electrons
in fact it's a frozen plasma in which
its nuclei are locked together in a
regular lattice
you might wonder how nuclei can bind to
each other given that they're all
positively charged and so should repel
well at these densities nuclei are
pushed so close together that their
mutual repulsion actually prevents
nuclei from slipping past each other
like gridlocked traffic
and the symmetry of that repulsion
forces nuclei into a regular grid
in this case the crystalline matter is
mostly iron that iron was the last
element forged in the core of the star
in the hours before it went supernova
and some of it still survives here at
the neutron star surface okay now the
real journey can begin as we start to
tunnel into the star's interior
we enter the outer crust of the star
density only increases as we go down
suffusing the crystal lattice is a gas
of electrons a so-called degenerate
fermi gas that holds up this part of the
star from further collapse
the deeper we go the more energetic
these electrons become and soon those
energies are high enough to drive some
very exotic nuclear reactions
electrons start to be driven into the
iron nuclei
in a process called electron capture
the negatively charged electrons merge
with positively charged protons to
produce neutrons in this way iron is
converted into elements with fewer
protons but which are still just as
heavy as iron and very very neutron rich
once we've gone down a few hundred
meters we see nuclei that can't even
exist outside a neutron star
where the star is 50 billion times the
density of the earth we might find a
nucleus like zinc 80 which would decay
in half a second on earth by ejecting
neutrons
nuclei with such high ratios of neutrons
to protons are only stabilized by the
incredible pressures and extreme
electron energies in the neutron star as
we leave the outer crust for the inner
crust our nuclei become so neutron rich
that they start to fall apart we call
this neutron drip neutrons leak from the
nuclei into the ever narrowing space
between them now we don't know exactly
how deep this phenomenon begins but our
best calculations suggest that it's
close to half a kilometer deep and we're
at least a trillion times the density of
matter on earth
we are really relying on our theoretical
calculations here we're beyond the point
where we can duplicate these energies
and these neutron-rich nuclei in
particle accelerators
as the neutron drip intensifies the
space between the nuclei fills with a
neutron gas
meanwhile the electron gas gets thinner
due to the electron capture process
in fact the neutron gas starts to take
over the role of the electrons neutrons
are also fermions and so two of them
can't occupy the same state the star is
now increasingly supported by neutron
degeneracy pressure but neutrons can get
much closer to each other before this
degeneracy pressure kicks in and so much
much higher densities become possible
further down the nuclei themselves start
to get fuzzy as protons are outnumbered
by neutrons five to one a given neutrons
wave function is so spread out that it
becomes hard to even localize it to
being inside a given nucleus
by the time we reach the bottom of the
crust around a kilometer deep densities
have reached 100 trillion times that of
the earth here the once distinct nuclei
are beginning to touch each other as we
drop beneath the inner crust things
finally start to get
properly weird
welcome to the pasta
specifically nuclear pasta this is
perhaps the least known and most freaky
state of matter in the universe
when nuclei start to touch they
rearrange forming exotic shapes
nuclei have a sort of competition while
neutrons and protons feel a very strong
short-range attraction to each other due
to the strong nuclear force
the electric repulsion between the
remaining protons tries to push them as
far away from each other as they can
down here there may be 20 neutrons for
each proton so the protons can't really
resist the forces reshaping nuclei
the result is this game of particle tug
and war with all this pushing and
pulling we see a complete rearrangement
of matter nuclei reform
radically
forming cylinders containing many
millions of protons and neutrons
nuclear physicists affectionately call
this phase of matter
spaghetti
at slightly higher densities this
nuclear spaghetti may be squeezed
together to form sheets
that's right nuclear lasagna
and because it's so dense it's really
hard to bend and move this stuff nuclear
pasta might even be the strongest
material in the universe a quintillion
times stronger than steel the enormous
strength of nuclear pasta allows it to
resist the insane gravitational forces
and so support a sort of jumbled texture
sort of like nuclear pasta mountains
buried beneath the star's surface
these could be as tall as 10 centimeters
which doesn't sound like a lot until you
remember that every cubic centimeter of
nuclear pasture weighs as much as a
mountain on earth as the neutron star
rotates these buried neutron star
mountain ranges get dragged in circles
making a very weak gravitational wave
signal these gravitational waves are
much weaker than the signals that we've
detected where neutron stars or black
holes merge and so it's much harder to
detect them
but instead of being a big splash and a
crash it's a continuous hum at exactly
one frequency twice the frequency of the
neutron star's rotation and
gravitational wave astronomers are
searching for these signals with ligo
right now
targeting pulsars in our galaxy using
their known rotation frequencies they
haven't found anything yet but they
might soon giving us the first glimpse
of the inner workings of neutron stars
by the time we reach the bottom of the
pasta layer just above the neutron star
core all of that matter has been
smooshed together into a soup with
mostly neutrons and just the occasional
proton the density here is 200 trillion
times anything found on earth and so
we've arrived at the core
where we find the most extreme
conditions in the entire modern universe
here pairs of spin half neutrons become
connected in a particular way to form
what we call cooper pairs which actually
act as single spin 0 or spin 1 particles
so some of our fermions effectively
become bosons which means that they can
do some pretty crazy stuff in the case
of neutrons they become a superfluid a
frictionless fluid that can do things
like sustained vortices with enormous
amounts of energy
some physicists think that the
dissipation of these vortices is seen by
us as glitches in the frequency in the
flashes of pulsars
the rare cooper pair protons on the
other hand turn the core into a
superconductor which is probably an
essential part of maintaining the
neutron star's enormous magnetic field
approaching the dead center of the
neutron star and even the protons and
neutrons start to lose structure and
mush together now this is all highly
theoretical but it may be that at these
extreme pressures and energies we find
hyper on particles containing strange
quarks
or they might not be bound into
particles at all the protons and
neutrons may dissolve completely into a
quark gluon plasma and we've talked
about quark stars before
while these plasmas have been seen in
collider experiments on earth we're not
sure if they exist in neutron stars
the only other time matter existed
naturally in conditions like these was
within a fraction of a second after the
big bang if you're quiet for a second
listen carefully
you might hear the faint booms of
thermonuclear storms raging above us on
the surface
it seems that our neutron star has
started accreting matter from a binary
partner star
its mass is growing and at some point
soon it will form an inescapable event
horizon
and will be stuck inside an actual black
hole
escape will become even more impossible
than it already is
i think it's time to power up our
anti-gravity boosters and leave behind
the strangest and most extreme parts in
all of space time
[Music]
you