Black holes
aren't what you think they are.
They're not holes, they're not black, and we can actually see them.
We've even managed to take a picture of one.
You are currently looking at something incredible,
the first ever image of a black hole,
the one at the centre of the
Messier 87 Galaxy,
55 million light years away.
Now we know there's a black hole at the centre of our galaxy,
the Milky Way, which is 27,000 light years from the solar system.
And we know that it's supermassive because in 2008,
Professor Andrea Ghez and her team measured how
big it was and found that it was four million times
more massive than the sun.
This measurement was such a big deal that in 2020
she won the Nobel Prize in physics.
To work this out, they studied the orbits of the stars
moving at incredible speeds around the black hole and use
this to weigh the black hole.
If there's a black hole at the centre of our galaxy, that's going to force these
objects that are really close to the black hole to move much faster
than they would move if there were no black hole.
So the first thing you want to see is that there are very fast-moving
objects where you think the black hole is.
If there's a black hole, there is a further prediction you can make about
what these stars are going to do.
They are going to move around the black hole on very short periods.
In other words, you're going to be able to see them move on more
than just straight lines as part
of their travel around the black hole.
These stars are going to move around the black hole because
of the gravity, just like planets move around the sun.
Contrary to their name and to common belief,
not all black holes are black.
In fact, the gas and dust that spirals around the black hole could be
accelerated to huge speeds,
which heats up due to friction causing it to glow.
In fact, feeding black holes as some of the brightest objects
in the entire universe.
There's a supermassive black hole in the centre of every galaxy.
So how do we know?
When quasars were first discovered, they were thought to be hugely bright
stars and any ideas of them being
black holes were dismissed as just crazy.
But we now know they are feeding black holes,
and they're described as 'feeding' because stars and gas clouds
that get too close are torn apart violently by the immense gravity and
then lost beyond the event horizon to become part of the black hole.
They're essentially like a little snack for the black hole.
There's a quasar at the centre of the Cygnus A galaxy that's a trillion times
brighter than our sun.
Dr Andy Fabian from the University of Cambridge is studying this quasar
with X-ray images. These help reveal the gas clouds that are orbiting
around the black hole.
There's a lot of other things going on out there,
and enormous amounts of
energy being released,
which we can only be aware of if we look with X-ray eyes.
We could see what was going on at the centre.
We could start to understand how the black hole was feeding energy out
into all the surrounding gas.
The friction generated by this dense atmosphere of gases produces the
hottest and most electrically-charged environment in the universe.
What we know is that the hotter something gets, the brighter it gets,
the more light it emits.
By feeding on all this gas, the black holes sometimes end up with just too
much material around them and end up burping out a load of it,
which then impacts the galaxy.
This can actually expel a lot of the gas that the galaxy would have used
to make more stars,
and essentially stopping the galaxy from growing any bigger.
So black holes seem to wield a worrying amount of power.
They can literally control how big a galaxy can grow.
Galaxies could, in a way, be much bigger than they currently are.
Something is stopping them growing larger,
and that's something is the black hole at the centre.
Now, this is bizarre because the ratio of the size of the black hole
to the size of the galaxy
is the same as the ratio between a grape or something this big
and the size of the earth.
It sounds impossible that something that small would have so much
control over something that big. But that is what's going on.
It's been calculated that the mass of a black hole is on average about
0.5 percent of the mass of a galaxy.
Essentially, the bigger the galaxy,
the bigger the black hole will be.
This correlation made
astronomers start to wonder whether black holes might have been
present or even responsible for the birth of their galaxy.
Because it really meant that there was something linking these tiny
supermassive black holes in the centre of galaxies with the whole
galaxy itself. It meant that somehow
their whole history had been intertwined, that the growth of the
galaxies and the growth of the black holes was somehow related.
Now, in the early universe, we don't know if stars formed first or
if black holes formed first, but
if the black hole formed first, then the galaxy of stars could have then
formed out of the gas that was swirling around it.
What everyone really wants to know though, is what happens when a star
gets swallowed by a black hole.
Well, a couple of years ago, a gas cloud called G2 came perilously
close to the event horizon of the black hole at the centre of our galaxy,
the Milky Way.
This is the first time really in human history that we have not only known
an event like this was
going to happen, but that we are prepared with the right sort of
technology to see the details unfold.
Astronomers monitoring the event were able to test the effects of the
black hole on this gas cloud.
It was essentially on a collision course with one of the most powerful
entities in the entire universe, and it was being stretched out
on its way there.
It is moving quite fast.
And it's not moving in a straight line, but it's a curved line.
And that's a very, very bad sign because it tells you, well,
there's something acting on it.
It tells you how gravity is pulling on that object.
Instead, though, it was 'spaghettified' and it circulated the black hole
and then was essentially
catapulted back out into space – lucky escape for the gas cloud.
This event confirmed that it is possible to get perilously close
to a black hole and still escape.
So there's a black hole at the centre of every galaxy and they have
the power to dominate everything around them.
But they're not just giant hoovers
sucking everything up around them. Stars, gas, dust, they're all happy
to orbit them with no issues.
We're seeing the black hole at the centre having a galaxy-wide effect
on the surroundings.
So if they really do have a galaxy-wide stronghold
and the one at the centre of the Milky Way has been there
since its existence,
that means that you, me and all the stars that we can see
have always and are currently right now orbiting
a supermassive black hole.