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IVY KUPEC: Sometimes you just can't get to know a scientist
until you sit down with them on a sofa or whatever. I'm Ivy
Kupec. I work at the National Science Foundation and a really
cool astronomer here named Dan Evans is a Program Officer here
from the Smithsonian Institution where he normally studies black
holes. I've always wanted to know more about this cosmic
conundrum so who better to ask. Hey, Dan.
DAN EVANS: Hey, Ivy, how's it going?
IVY: Pretty good. I just wondered if you wanted to get a
cup of coffee or some tea?
DAN: Yeah, sure, let's do it.
IVY: Hey, so how's your daughter been? You've been
building any forts lately with your daughter?
DAN: Yeah, I have actually. She's a Lego genius.
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IVY: So the reason I was really excited about getting together
with you I had this dream the other night, I don't know if I
told you this, that I was on the edge of the earth because we
were about to fall into a wormhole, the whole planet was,
and it seemed so funny because I was thinking earlier in the day
about your black hole research and then it made me wonder, so
what is a black hole exactly then and if they're black,
how do you ever see them?
DAN: So a black hole is a region of space and time that is
so infinitely dense that nothing not even light can escape
through it, okay, and that's cool. So that means that black
holes by that very definition are black, so although the black
holes are black they're remarkably simple objects
and they glow like fireworks at least in x-ray lights when
material falls down them. Let's imagine that you're watching
water go down the drain, the water starts off, it goes –
swells, swells around very, very slowly and then as it approaches
the center of the drain it rapidly, rapidly spins. Very,
very similar in a black hole, okay. So as material falls
down, it rubs together so ferociously with so much
viscosity and, in fact, a lot of magnetic fields as well,
the giant bursts of x-rays flares are released just as the
material takes its last plunge into the hole.
IVY: How do black holes even ever – how do they come
to be made?
DAN: I knew you were going to ask me that.
That's a really tough question. There are different
theories. Let me start by saying that there are two
different types of black holes; stellar mass and super-massive.
The stellar-mass ones have pretty small masses any where
between four and twenty times that of our sun.
The ones that I study the super-massive,
these are sort of billion to a million solar
mass beasts. They probably have very different
origins. For the stellar-mass black holes we think they
originated when a star exploded into a supernova and the
resulting collapse actually created the black hole. For the
supermassive ones, it's anybody's guess, but the best
theories of it in the infant universe, there were massive
halos of dark matter that slowly collapsed underneath their own
weight and because the densities were so high that a black hole
formed at the center.
IVY: Do they bump into each other or merge with each other
and things like that along the way?
DAN: The black holes merge quite often in fact, we think.
They sort of spiral around each other in a cosmic dance before
coming together and then merging with a ferocious release of
gravitational radiation which we're also trying to
detect as well.
IVY: Are there a lot of them out in the universe?
DAN: Yes. Every single galaxy that we know of hosts a
super-massive black hole at its heart, every single one.
IVY: Really?
DAN: But the mass of that black hole is anywhere between a
million and a billion times that of our sun and we know easily of
300 hundred billion galaxies, and that's just the fraction
that we've observed. They're probably infinite numbers of
galaxies and, therefore infinite numbers of black holes
at their heart.
IVY: I know, you showed a picture of your daughter during
a talk. Young children are sometimes, it's through their
eyes it's best to think about things like black holes, even,
am I recounting that correctly?
DAN: You're right, what I basically always say is our
children make great astronomers because they view the world with
such simplicity. It's actually true. I can still speak to her
and she's two and a half and she'll point at something and
say "big truck." It's wonderful. They have two
parameters, right, and black holes aren't much more
complicated than that. In fact, they're probably the simplest
objects in the universe.
IVY: Then why don't we understand them better?
DAN: So the devil's in the details. So black holes are
fully and completely described by just three quantities; their
mass, their spin, otherwise known as their angular momentum,
and then their charge, that's it. Now, you try describing
anything with just three parameters, you can't do it.
IVY: So what is some of your research involved with black
holes, your research, specifically?
DAN: What I've really tried to do is to understand how the
black holes are spinning, okay. This is a fundamental test of
Einstein's general theory of relativity, okay. So if we can
measure the spin of a black hole and compare to his predictions
then we can actually begin to understand whether general
relativity is correct or whether we need a modification to it.
The other thing that I've really spent a lot of time doing is
investigating jets. Jets are awesome, okay, so material falls
into the black hole and just the vicinity of the black hole,
giant jets are shot up. They race outwards from the black
hole pretty much at the speed of light, a little bit less,
and they can go up many, many, many millions of light years.
IVY: What's going to be – what's on the horizon for
the black hole research?
DAN: It's interesting that you that word "horizon." So the
next big thing with black holes is to image one.
IVY: Of course.
DAN: Okay. This is cool, so it might seem like a flight of
fancy to construct a telescope the size of the earth, say, but
teams of astronomers are planning on doing just that.
Obviously, they're not going to cover the entire globe's surface
with concrete, but they can link together digitally different
telescopes across the world to synthesize one giant telescope
with diameter that's equivalent to that of the earth. The idea
behind it is that you need such a massive diameter to have such
sharp resolution that you can image the actual silhouette of a
black hole. It's going to happen. I'm absolutely
convinced of it. It'll probably happen within the decade.
IVY: That's amazingly close.
DAN: Yeah, so we've just made a massive award within our
division to enable one such telescope called
the Event Horizon telescope.
IVY: Oh, no kidding.
DAN: And we are completely excited about what it's going to
do, we're kind of giddy over it.
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This was so much fun.
IVY: It was. We should do this more often.
DAN: Any time. All the best.
IVY: Thanks. Great. Take care.
DAN: See you.
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