Black holes are like gigantic vacuum cleaners
-- the end point in the lives of really big stars.
.Before black holes were ever discovered, people
thought about the possibility of very heavy
stars squashed into a relatively small volume
such that their gravity is so strong not even
light can escape their grip.
James Bradley was an astronomer royal at the
Observatory in Greenwich and one of the amazing
things he did was to work out an accurate
value for the speed of light.
This value was needed to calculate how heavy
a star must be to pull light in and swallow it.
300 years later, one of the astronomers at
the Observatory would like to investigate
a REAL black hole.
Liz would like to know what would happen to
her if she approached one and would particularly
like to know what could be inside.
The tricky bit is finding one to begin with.
The black hole itself is invisible -- instead
astronomers look for the powerful effects
they exert on nearby matter.
Sometimes this is seen as material swirling
around a greedy black hole, but those without
cosmic buffets close by are harder to spot.
However, if we look towards the centre of
our Milky Way we see lots of stars circling
an invisible object.
These stars have similar orbits to the planets
in our Solar System which helps us work out
that there is something in the middle -- a
supermassive black hole.
The one in our galaxy is nearly a quarter
of a million trillion kilometres away so we
are in no danger of being pulled in.
So what would happen to Liz if she approached
a black hole? Well near the boundary called
the event horizon, she would feel the effects
of the strong gravitational forces from this
collapsed star.
At the point of the event horizon Liz would
have to travel at the speed of light to escape
the gravity of the black hole... and this
is impossible for her or any object to achieve!
Also the strong gravitational field would
slow down time.
If we could see Liz's watch from our perspective
here on Earth it would appear to us to tick
a lot slower than our watches, although time
for her would pass by normally. Eventually,
after a few years sat outside the event horizon
of the black hole, Liz would be shocked to
know that thousands of years may have passed
back home on Earth. It's as if the black hole
is a time traveling machine, allowing Liz
to travel into the future.
Also, from our perspective we would see her
become redder and redder until she disappeared
-- the strong gravity would stretch the light
to longer wavelength, low energy light that
we can't see with our eyes. This would happen
before she crossed the event horizon, but
what would happen to Liz if she stepped in?
Well if she fell in feet first, her feet would
be pulled further along than her head so she
would have to endure... spaghettification!
She would be ripped apart and pulled in to
the centre, the singularity - an exotic region
of zero volume and infinite gravity... or
is it?
Liz wisely decides not to go in but thinks
about the possibilities for what she would
find inside.
Some physicists believe if Liz jumped in,
there would be no sign of her presence inside
the black hole apart from a slight increase
in its mass. The cosmologist Stephen Hawking
believes that particles can tunnel out so
that eventually over time black holes evaporate.
We may not ever know if we can retrieve information
from a black hole.
Some physicists think that the event horizon
acts as a veil blocking our view of the weird
physics happening inside. Some theorise that
the fabric of space is punctured at the singularity.
American physicist Lee Smolin suggests that
time ends inside a black hole and begins with
the start of a new Universe, forever hidden
from our view.
A popular theory for the nature of a black
hole brings in the idea of a ball of vibrating
strings. These strings would keep information
about the contents -- Liz's atoms would be
shredded into their constituent strings and
would merge with the existing orchestra inside...
it's Liz but not as we know her!
We might not ever know for sure what's inside
a black hole, but it is fun thinking about
what could be happening... and who knows,
Liz may end up in a whole other Universe with
its very own Greenwich Observatory!
