So now we'll move on to x-ray. And for
x-ray I have picked this object - oh look,
it's a fuzzy blob! This is an object
called the Crab Nebula. And so the Crab
Nebula is in this part of the sky, so
here's Orion, there's his belt,
there's Betelgeuse, and you sort of go
up from there to get to this part of the
sky. And many of you will probably be familiar
with the Crab Nebula even if you don't
realize it, because the Hubble image of
the Crab Nebula is one the most
recognisable, most famous astronomical
images, I think. So many of you will have
seen, hopefully, this picture before. So
the Crab Nebula is what we call a
supernova remnant. It's what's been left
over when a star much more massive than
the Sun has exploded at the end of its
life. And so what we see here is the gas
that's been flung out in that explosion.
This is actually a supernova that went
off - Chinese
astronomers observed it in 1054. They
suddenly saw what looked like a new star
appear in the sky. And we're waiting for
that to happen,
actually, with Betelgeuse so one of
Orion's armpits or shoulders, if you don't want
to think of them as his armpits,
that star is at the end of its life and
it's a much more massive star than the
Sun, and it is going to go supernova soon.
But when astronomers say soon, it could
be tomorrow, it could be in 10,000 years,
so no one hold your breath on it, but
every time I'm out in the winter because
Orion, we see him in the winter night sky,
I do always look up at Betelgeuse just
to check that it hasn't gone supernova.
Because can you imagine how annoyed
you'd be if it did go supernova and you
were outside and you hadn't noticed. So keep an
eye on Betelgeuse for us. The reason I
want to show you this object for x-ray,
though, is not to do with this gas
that's flung out, not to do with the
nebula, but what's left in the centre. So
when this massive star explodes the
outer layers, as I said, get flung off in
the explosion - this is all the gas that
we see spreading out now. But the core of
it collapses down and it condenses down,
in the case of this star into what we
call a neutron star. So this is a star
that's made up entirely of neutrons, of
the neutral parts of the atom. And some
neutron stars spin, as this one does. And
we can actually see that in the x-ray. So
I think this is absolutely incredible,
because this is the leftover bit of that
star. And can you see these two jets
coming out of it? This neutron star is
spinning, so it's what we call a
pulsar. You can think of these as sort of
cosmic lighthouses - they've got these two
beams that come out, and as it spins
those beams pass by us. It's spinning
really fast - this one's spinning at
something like, those beams will come
past us something like 30 times a second,
I think. And they spin so accurately that
you can time that beam coming past you
and it's often more accurate than atomic
clocks. I can't remember if it is
currently more accurate than atomic
clock,s because they keep on making more
accurate atomic clocks and then they
find better pulsars, and then more
accurate atomic clocks, so it's kind of
constant battle between the two, but
these are ridiculously accurate timers.
And this was taken with another space
x-ray telescope, the Chandra X-ray
Observatory. And of course we have to put
these x-ray telescopes in space because
our atmosphere stops those x-rays from
coming down to us on earth, which is good
because otherwise we'd be fried by the x-rays.
