The Truth and Lies about Black Holes
NASA: We have booster ignition and liftoff
of Columbia, reaching new heights for women
and X-ray Astronomy.
Martin Elvis: The main thing Chandra does
is take these superb, sharp images.
Narrator: Black holes have a bad reputation.
After all, something that could swallow you
completely sounds pretty scary. They're invisible,
so maybe there's one just around the corner
and we don't know it! Also, aren't they enormous
vacuum cleaners capable of destroying anything
that gets near them? Once the black hole starts
pulling on something, isn't that just a one-way
ticket to oblivion? Well, not all of these
things are exactly true. Dr. Paul Green of
the Chandra X-ray Center helps us tackle some
of these black hole misconceptions.
Scientist: First off, we can't see inside
a black hole, because anything that goes over
the edge is gone forever. So that's partly
where the name comes from. But it's often
true that only a small fraction of the material
near a black hole falls in, while most of
it just circles forever. The stuff falling
close in toward the black hole gets superheated,
and we can see that in X-rays with Chandra.
Let's use a hypothetical situation to think
about the effects near a black hole. Suppose
that our Sun were replaced overnight by a
black hole. The truth is: the Earth wouldn't
budge. That's because our orbit is determined
only by the mass of the Earth and the Sun
and the distance between them. As long as
the black hole still had the same mass as
the Sun, we'd stay in the same orbit. This
shows that black holes don't always suck everything
in. In fact, if they did, wouldn't the entire
Universe have been digested into one big black
hole by now?
Narrator: Let's listen to Paul Green explain
how the scene around a black hole is certainly
more complicated than just a simple cosmic
vacuum cleaner
Scientist:Think about water going into a drain.
Water never goes straight down a drain. Instead,
it always forms a vortex or whirlpool, and
the reason for this is because it always has
some spin to it. The same is true of the gas
and dust that funnel into a black hole. If
the matter can't lose its spin, it will just
go into orbit as a disk around the black hole.
It's called an accretion disk.
Within the accretion disks around black holes,
the atoms and molecules jostle each other
with increasing ferocity as they rub together
in a spiraling mosh-pit death dance as they
are pulled towards the hole. So in some ways,
these particles are fighting for their cosmic
lives. And some of them will win.
Narrator:If not everything around a black
hole is doomed, what happens to that majority
of stuff that doesn't fall in? Paul Green
explains.
Scientist: The material falling around the
black hole can never reach the black hole
itself unless it loses enough angular momentum.
One way this happens is through outflows.
That's right, black holes don't only suck
in material, they also blow it out. Nearly
every black hole that is accreting matter
is also expelling it. This happens while the
matter is still outside the black hole itself,
since as we know nothing can escape once it's
within the radius of the hole.
Narrator:So now we know black holes just don't
take stuff in, they send it out into space.
And, this isn't just for fun. This affects
the environment around them, as Paul Green
describes.
Scientist: Black holes form jets and winds
of spectacular power and variety. The matter
is expelled in many cases at huge velocities,
close to the speed of light. Sometimes outflows
shut off the black hole's own fuel supply
of inflowing matter. But these energetic outflows
can also have profound effects on the environment
of the black hole. Outflows from supermassive
black holes may shut off the growth of galaxies
or even stop the inflow of gas towards the
centers of galaxy clusters.
Narrator:So black holes aren't entirely black.
And, they aren't just the harbingers of destruction
that their name might suggest. In other words,
maybe they aren't something just to be afraid
of, but also to be in awe over. It turns out
that black holes are an incredibly important
part of our cosmic ecosystem. The more we
learn about black holes, the more it seems
we should be glad
that they are around.
