so neutron stars are also pretty cool if
a star is too heavy to die as a white
dwarf then the next best thing is a
neutron star what happens is remember
that those electrons are snobbish and
they don't want to get in each other's
faces well they look around and go hmm
tasty little proton I like him so what
happens is that the electrons rather
than getting in each other's faces the
electrons combine with the protons to
form neutrons so you get a ball of
neutrons all right so in a supernova
explosion the outer part of the star
explodes and the inner part will
collapse down to a neutron star as long
as it's not more than about two or two
and a half times the mass of the Sun and
so you have a little ball of fast
rotating neutrons about twice the mass
of the Sun only about 15 miles wide
incredibly dense we're talking about
billions of tons per tablespoon really
really really dense denser than baklava
which is which I love but which is
really dense okay all right so how can
you find a spinning ball of neutrons
that's only 15 miles wide well the
answer is you can't find it unless it's
doing something that brings attention to
itself and many many neutron stars do
exactly that we discover them because of
behavior that we call a pulsar so here
is my badly drawn you're used to this by
now example of a neutron star so stars
rotate dead stars rotate as well so this
ball of neutrons is spinning it's
rotating around its North and South Pole
like the earth remember our sun has a
magnetic field stars have magnetic
fields and like the earth the rotational
axis of this star is not exactly the
same direction as the magnetic axis so
if you follow a compass on the earth it
will not lead you to Santa Claus Santa
Claus lives at
North Geographic or North rotational
Pole of the earth a compass leads you to
the Magnetic Pole fortunately on earth
they're not that different but let's
imagine that there's a nice angle
between the rotation Pole and the
Magnetic Pole so as this thing is
rotating imagine the North Magnetic Pole
coming and spinning around towards you
and away from you okay now there's one
more thing we need here the other thing
we need is we need some free electrons
or protons floating around on the
surface of this ball of neutrons those
charged particles interact with the
magnetic field so hopefully you've seen
a picture with a magnetic field with
these magnetic field lines looping
around when you have electrons or
protons in a magnetic field they'll get
wrapped up in the magnetic field lines
and will start going wee and whirling
around and as they do that they will
emit energy they will emit
electromagnetic waves often radio waves
and those radio waves get channeled out
of the magnetic poles okay rapidly
rotating strong magnetic field a few
free electrons and protons which will
spin around give off radio waves the
radio waves are channeled out the North
and South Magnetic Pole so what happens
is as this thing spins around you will
see alternating pulses of radio waves
radio wave radio wave radio wave radio
wave as it's spinning around this is
called the lighthouse model of a pulsar I'll
try to demonstrate this without killing
myself okay so this is my rotational
axis and this is going to be my magnetic
axis okay and so this would be my North
Magnetic Pole and this would be my South
magnetic pole and you're going to have
to imagine that there's radio waves
coming up okay feel like I'm doing the
chicken dance all right so here we have
my North Magnetic Pole and my South
Magnetic Pole every time one of my
elbows goes in front
of you you're going to imagine that
you're feeling a pulse of radio waves
and so if you had a radio telescope you
would have no signal pulse no signal
pulse no signal pulse and those pulses
would be incredibly rapid and incredibly
evenly spaced because of the fact that
this thing is spinning like clock
