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Black holes are wild.

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Yes, they are the most compact things
we know of, so dense

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that even past a certain point,
light cannot escape.

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Even though we can't 
 see inside them,

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the environments 
around black holes

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are brimming with bizarre activity.

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There can be a corona 
of hot electrons

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that occasionally spits out

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scattered X-rays.

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There's a bright accretion
disk of gas and dust

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whose light is so warped by gravity

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you can see the near and far sides

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at the same time.

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And I can't even begin to wrap my head
around this estimate:

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There can be jets
20 million light-years across.

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That is 140 Milky Ways

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end-to-end.

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So if we can't see black holes themselves,

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we need other ways 
of understanding them,

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like these extreme surroundings.

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That's why NASA continues 
to create new instruments

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to decode the chaos.

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So is there anything

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common about a black hole environment?

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Let's break down what we know it.

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How does that process happen?

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How we know it?

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Where do you start with this?

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What am I looking at here?

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If you look closely, it's a big mess.

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And why we need to keep the questions coming.

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This is black hole environments explained.

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Not all black holes 
are the same  

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 or even chaotic.

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So scientists currently categorize
black holes into four types.

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There are the ones that we've 
theorized exist

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like tiny primordial black holes,

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which formed shortly after the big bang.

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And intermediate-mass black holes

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that are sort of missing in the sense

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that they should be there

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but we haven't confirmed sighting.

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We've observed plenty 
of stellar-mass black holes

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that are at least eight times
the mass of our Sun,

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and the leftovers of supernovae.

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The most dramatic by far,

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are the supermassive black holes,

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which are hundreds of thousands 

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to billions of times
more massive than our Sun.

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In fact, they can reach sizes so big 

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they can span

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our entire solar system.

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When they're at the centers of galaxies,

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these monster black holes
can become active galactic nuclei,

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or AGN. 

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They fling a lot of material
and they produce a lot of kinds of light.

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AGN are black holes 
at their wildest.

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Jenna Cann researches 
black holes

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and their signatures
here at NASA Goddard.

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She agrees that AGN 
are the drama queens of space.

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I would call them the divas instead,

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but when you have an AGN, 
they want you

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to notice them
as much as possible.

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They're singing in every 
single wavelength they can.

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But if you're looking at a full galaxy,

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do you almost just assume

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that there's a black hole there?

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When we have a massive galaxy, 

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something that is like a billion times 
the mass of our Sun,

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we can pretty much safely assume
there's going to be a black hole in there.

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When you get to the low-mass galaxies,
which are the ones that I like studying the most,

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we don't know what's going on in them.

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But when you have a low-mass AGN,

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that light can be easily overshadowed
by stars and everything there.

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So, you really need
some kind of unambiguous

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stars can't mess around with this diagnostic.

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Where do you start with this? Right.

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You get a map of dots.

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And these dots mean what?

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What we'll do is take a spectra of our galaxy.

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and if we see 
highly ionized high-energy features,

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that’s good evidence
that there is going to be an AGN there.

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Would you say that this is the best
indicator of a black hole?

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That is very contentious!

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There is no one best option, basically.

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Every single tool that we have
right now is fallible in some way,

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doesn't work in some environment.

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Enough talking about this 
environment like it's all uniform.

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We need a lesson in AGN anatomy.

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An AGN can have 
several different structures.

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The brightest feature
is the accretion disk.

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In this Event Horizon Telescope
radio image,

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we see the accretion disk 
around a supermassive black hole

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called M87*.

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This plane of gas and dust 
orbits the black hole

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and heats up through 
gravitational and frictional forces.

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It emits light all the way 
from radio to X-rays.

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Above and below the disk 
an AGN can have a corona.

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This superheated plasma 
of loose electrons

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emits a lot of X-rays.

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It's way less dense
than the accretion disk

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but way hotter.

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For a long time, scientists
wondered how the corona formed,

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how it was shaped, how it interacted
with the rest of the environment.

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So a recent study with 
NASA's IXPE telescope

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shows that the observed coronas 

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likely extend in a plane
like the accretion disk

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and possibly are a lot larger
than we previously thought.

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One of the best methods
to learning more about these systems

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is through analyzing
something we call coronal lines.

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Now Jenna uses spectroscopy to investigate 
coronal lines in AGN spectra.

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Yes, they look like 
squiggly graphs,

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but they tell us what 
elements are present

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and more importantly,
 what isn't present.

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So, a lot of the elements are ionized

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and are missing their electrons.

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So these are highly ionized
emission lines.

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Six electrons have been 
removed from that ion.

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It's very, very bright in the center,
which makes sense.

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That's the nucleus,
that’s going to be the brightest there.

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And then it gets dimmer
and dimmer as you go farther out.

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And they're pretty good evidence to there
being an accreting black hole in there.

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Because it takes a lot of energy
to even produce the ions

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that produce this emission.

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Despite AGN being some of the brightest
objects in the universe,

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they can also sometimes
hide behind 

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 a dusty torus.

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Now a torus is a thick,
bagel-shaped structure

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that is so dense we can't see the AGN

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unless the bagel’s hole is facing
one of our telescopes

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or you seek the energetic X-ray signals.

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Now, scientists using NASA's
NuStar mission, another X-ray telescope,

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think that as many as 50% of black holes 
are obscured by a torus.

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These dusty cloaks

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can even impact a developing galaxy.

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A lot of that thick debris
will make its way towards the black hole.

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And if too much of the dust
falls towards it at once,

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it can cause the black hole
 to sort of cough or burp

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and a bunch of material

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comes out, and a hiccup that is big enough

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can even slow the rate of star formation.

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All of that is nothing

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compared to the achievements 

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of a jet.

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So remember M87? 

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Here's another image of it
taken by our Hubble telescope.

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See that?

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That bright line is a black hole

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throwing a huge jet of particles

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moving at nearly the speed of light.

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It does make you wonder

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if black holes gather
everything that comes too close,

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how does it propel particle jets?

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Cecilia Chirenti,
an expert in math, physics,

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and the wonders of black holes,

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has some ideas how.

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So what is going on?

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Why are they ejecting a lot of things
when it seems like

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what we know is that they suck things up?

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If you look closely, it's a big mess.

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If you haven't ever seen it before,

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you have to imagine
that the black hole is in the center,

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the accretion disk is around it.

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Kind of think about, you know, the

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the rings of Saturn 
that are around the planet.

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You have this big accretion
disk around a black hole

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and the jet is coming out like that.

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So you can think of a garden hose,
you know, when it's

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spraying out there in
 the cosmic distances, right?

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Like really big.

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The matter in the jet
has to be coming from somewhere.

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So it's coming from the disk.

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And the question is: 

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How do the particles on the disk,

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how do they get accelerated, pulled out

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from the disk

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and directed outwards on the jet?

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So that is the mechanism
that people try to study,

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and we have some ideas of how that works.

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Because if the black hole is spinning,

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you can 

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steal a little bit of that 
rotational energy of the black hole

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and give it to something else.

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Cecilia went on to explain that these jets

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also form because of a 
black hole's magnetic fields.

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With the magnetic fields,

187
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what happens is that

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they are stealing a little bit of the energy,

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the rotational energy from the black hole.

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This extra energy in the magnetic fields
is what is accelerating the particles

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in the disk to form a jet.

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That is kind of like the 
particle accelerators on Earth

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where we use magnetic fields
for accelerating particles.

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Well beyond the black hole,

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the jet, the ionized and the energized
particles, the X-rays and such,

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the gases just continue to spread.

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Because of their very nature,

198
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we will never see beyond
a black hole's event horizon.

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We are doomed to see
only the light that surrounds them.

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But there's still so many questions
we can answer with that light.

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And with each new telescope
we build, 

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whether it peers through our atmosphere from the ground,

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or studies the cosmos from space,

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they give us more clues as to how

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and why black hole environments 
 behave as they do.