There are number of ways that you can think
about black holes, but one nice way in to
the subject is to think about something that's
much more familiar. Thinking about escape
velocity. Let me describe what I mean through
a couple of sequences here. So imagine that
you are on the surface of the earth. Let's
sort of zoom down right to our planet and
we ask ourselves if we fire a projectile from
the surface of the earth upward, what will
happen? And we all pretty much know what will
happen, right? So if we take a cannon and
we fire a cannonball at a fairly modest speed,
it's going to go up, it's going to come back
down. If we fire it with a somewhat larger
speed, it'll go up higher, but still it'll
come back down. But finally, if we launch
it with the right speed, it will go up and
it will just barely escape the gravitational
pull of the earth and it will go off into
space. And that speed required for that to
happen is what we call escape velocity at
the surface of the earth.
Now, what is the escape velocity at the surface
of the earth? Yeah, someone actually said
it. It was 11 point two kilometers per second.
Thank you. Wow. A gold star in the back there.
About 11 kilometers per second is what you
need at the surface of the earth. But here's
the question, if you were to look at a different
planet, one that's bigger than the earth,
what will happen? Well, again, you can pretty
much picture what will happen? If it's bigger,
it's more massive. You're going to need a
bigger cannon to fire that cannonball with
higher speed because the escape velocity will
go up. It will be larger than it is at the
surface of the earth. But of course if you
had that big cannon, you actually fire it,
the cannonball will go up, and again, if its
speed is bigger than the escape velocity,
it will be able to get away.
But now I want you to think about something
a little bit less familiar. Imagine that this
canon is not firing cannonballs, but is firing
balls of light. Photons. Now light goes really
quickly, right? I mean light speed... What
is the speed of light? Everybody uses different
units, which is nice. 671 million miles per
hour. 300 million per second, right? And meters
per second, I should say. So at that high
speed, of course light will easily be able
to escape and be able to go off into space.
But here is the interesting thought experiment,
and this is a thought experiment that goes
way back. This is an experiment that this
fellow over here, John Mitchell, this is in
the 1700s, right? Long time ago. He asked
the following question. He said, look, what
if you were to imagine looking at, say, a
star like the sun.
Now, clearly, the escape velocity at the surface
of the sun is much less than the speed of
light. So certainly all the light that the
sun emits easily gets away, but just as the
escape velocity of a planet goes up, if you
make it bigger, more massive, he asked, well,
the same should happen for a star. So let's
imagine making the star bigger where the escape
velocity goes up. Now, if it's still less
than the speed of light, the light will get
away. But he asked what would happen if you
made the star so big that the escape velocity
at its surface will be bigger than the speed
of light, right? In that case, he imagined
that if you made that gigantically massive
star, light could not get away. The escape
velocity will be bigger than the speed of
light and if light doesn't get away, the star
would go dark. A dark star, and this is again
in the 1700s, right?
So he is thinking purely in a Newtonian framework.
That's the only description of gravity that
we had back then. So the natural question
is, is this musing of John Mitchell? Right?
This theologian, this natural philosopher
from the 18th century. Does this idea have
relevance when you start to think about gravity
in the manner that was given to us by this
fellow over here, Albert Einstein. Because
I think as we all know in the early years
of the 20th century, Einstein rethought our
understanding of gravity and he gave us the
general theory of relativity in which gravity
is now thought of in a completely new way,
not the Newtonian description. Gravity, is
thought of as warps and curves in the fabric
of space and time. So Einstein takes this
idea, this new way of thinking about gravity.
He writes his famous paper on the general
theory of relativity. This is in 1915, his
paper becomes widely circulated and indeed
about a year later, 1916 on the Russian front,
there's a German astronomer, mathematician
named Karl Schwarzschild. And he's out there
in the trenches charged with calculating artillery
trajectories and somehow just by coincidence
what happens is Einstein's paper just kind
of goes by.
He grabs a hold of it and he gets so captivated
by Einstein's ideas that he forgets about
artillery trajectories and starts to calculate
with general relativity and he finds that
if you have a spherical body that you crushed
down to a very small size, according to Einstein's
math, the warp and the fabric of space will
be so extreme that nothing can pull away.
Not even light can pull away. So it's now
a modern day version, if you will, of what
John Mitchell had imagined. An object that
goes black because light cannot pull away
from it. So roughly speaking, it would be
as if you had a flashlight near the edge of
one of these objects. And when you turn on
the light, instead of a light going off into
space like it's pulled down into the hole,
into the black hole. This is the modern day
version of what a black hole would be.
Now the term black hole, it turned out this
was coined on a 112th Street and Broadway.
I'm not joking. At the Goddard Institute of
Space Studies on 112th and Broadway, John
Wheeler was giving a talk and this way of
describing these dark stars came up and Wheeler
pushed this idea. He popularized and say he
advanced our understanding of it, but this
is where the term black hole comes from. Now
this of course is a sort of cartoon version
that gets it the basic idea. For those that
want to see it a little bit more precisely,
here's really what goes on near the vicinity
of a black hole. And if you don't understand
this, it doesn't matter. We can put down a
space time diagram, if you remember from high
school. This is where we have time on this
vertical axis and you set off a beam of light
that fills out a cone, so called light cone,
and what happens is, the geometry of space
and time is so distorted by a black hole that
beyond what's called the event horizon, the
direction of time and space is so twisted
that as light propagates, it cannot get out
of the edge.
It cannot go beyond the event horizon of the
black hole, and that's why no light can get
out. That's why the black hole is black. Now,
natural question is, okay, these are interesting
ideas, but how in the world would one of these
objects come to be? And people began to think
about this idea for a long time, thirties,
forties, fifties, and let me give you one
possible scenario by which the kind of object
we're looking at, a black hole, would form.
And for that we can imagine that we have a
large star, like a red giant. To support its
incredible weight, this star has nuclear processes
taking place in the core that generate heat
and light and pressure that props the star
up, but sooner or later the star uses up all
of its nuclear, fuel and at that point it
can't support its own weight, so it begins
to implode and as it implodes, it gets hotter
and denser.
Finally, setting off an explosion that ripples
through the star and when the explosion reaches
the surface of the star, it causes the outer
layers to explode and what remains if the
star was big enough to begin with is a tiny
core, a dense core that can no longer support
its own weight at all, and it will collapse
all the way down into one of these objects,
these black holes. That's the idea of how
these objects could form. And what we'd like
to do here tonight is explore our current
thinking about these objects. Are they real?
How would we actually see them and can we
get any insight into what happens inside of
these spectacular objects? And to do that,
we're gonna bring out some experts who spent
their careers examining these very questions
and let's get to them right now.
So our first guest is one of the world's leading
experts in observational astrophysics who
heads UCLA's Galactic Center Group, best known
for her groundbreaking insights on the center
of our galaxy. She is the winner of, among
other things, the Crafoord Prize in Astronomy
from the Royal Swedish Academy of Science
and a MacArthur fellow. Please welcome Andrea
Ghez.
Also joining us, there's an astronomer at
the Harvard Smithsonian Center for Astrophysics
who leads an international collaborative project
called the Event Horizon Telescope, whose
goal is to change the edge, the event horizon
of a black hole. So please welcome Shep Doeleman.
All right, so thank you both for joining us
here tonight. Let me just begin with sort
of one general question. So people have been
thinking about this idea of black holes for
a long time. As I said, all the way back in
the 1700s and a lot of research has been done,
thousands of pages of calculations. Do you
think that there are really black holes out
there or are theorists' imaginations overworked?
I think it's pretty clear that there are black
holes out there. Of course I'm a little biased.
Since you've spent your life trying to observe
them. Yes, that's it.
It's important to think about the fact that
there are two kinds of black holes, black
holes, and you were just talking about, the
ones that come from the lifespan of stars,
and then the supermassive black holes that
we think are at the center of the galaxy-
And those are the ones that you've actually
been studying in some detail, so look, we're
going to get to those in just a moment. But
Shep, your general view is more or less the
same or do you think there's a chance that
it's a red herring, that these black things
are not really out there?
Oh no, it's beyond the shadow of a doubt.
I really think it exists. I mean, there's
all these lines of evidence. You know, we
see these terrifying engines at the centers
of galaxies that spew out these jets on either
side of them, and the only thing that can
power them are supermassive black holes. So
everything is pointing to the fact that these
really do exist.
Good. So I'm glad you're saying that because
had you both said no, I don't know what we
do with the rest of discussion here today,
but that's great.
So. So Andrea, your work as I understand it,
has been focused on the center of the Milky
Way Galaxy. So first of all, just give us
some sense of what you think is residing in
the center of our galaxy, and then we'll try
to look at the evidence that led you to come
to that conclusion.
So we're pretty convinced that there is a
super massive black hole at the center of
our galaxy and
How big is supermassive?
When we say super massive, we mean a million...
in the case of our own galaxy, 4 million times
the mass of the sun. And in terms of these
really big ones that are at the center of
galaxies, that's on the low end, because we
think about things that are a million to a
billion times the mass of the sun.
And for a million solar mass black hole, like
how, like for the sun, let's maybe start simple.
If the sun was turned into a black hole, how,
what would its radius be?
It would be about the size of a college campus.
Now it depends on which college you're talking
about, but-
Let's talk about NYU.
Good. Uh, so, so a couple kilometers
across. For the one in the center of the galaxy,
how big do we think it is?
It's about 10 times the size of the sun. So
about 10 million kilometers.
So it's a big object. But it still follows
the same basic pattern that it has an edge,
an event horizon, and all of the standard
lore would apply to it. It's just on a bigger
scale.
It just scales simply with mass, so the math
is simple.
So, so, so what evidence do you have that
it is a black hole? Can you sort of take us
through that?
Yeah. So to prove that there's a black hole
directly, what you want to do is you want
to, you want to show that there's a lot of
mass inside a small volume or inside a small
region. In particular, you'd like to show
that it's confined within its short shield
radius that you were just talking about.
So Schwarzschild radius is the radius for
a given mass where if you can crush the mass
within that radius, it will naturally turn
into a black hole.
Right. And so that's why we're at the size
that we're talking about because of course
a black hole itself is infinitesimally small.
So this isn't the abstract size. And so our
job-
Just clarify that. So when you say that, you're
talking about when the black hole forms, the
matter crushes down to a small size.
Yeah. So the idea of the Schwarzschild radius
is that no light can escape it, as we were
just talking about. But it's also true that
once you get the mass to that scale, gravity
will overcome all other known forces and there's
nothing that can stop the collapse of the
object. So from a scientific point of view,
once you've shown that a mass is within its
Schwarzschild radius, you have come up with
for the proof of a black hole. So from the
point of view of somebody who's hunting for
black holes, your job is to show that there
is some amount of mass inside a small volume.
So the way we've approached it at the center
of the galaxy is to look for the stars that
are at the heart of the galaxy and to develop
techniques that allow us to not only see the
stars that are that close, but that allow
us to observe how they go around the center.
So if you want to find the center of the galaxy,
you can look up in the night sky and find
the constellation of Sagittarius. It Is the
teapot and the teapot pours into the center
of the galaxy.
Is that right?
That's your roadmap.
So convenient.
And if you look up at the night sky, not in
of course New York, but in a place that you
can actually see the night sky, you can see
the Milky Way and the Milky Way is that band
of white light that comes from the stars,
but there's also a lack of light which is
from all the dust. So you can't actually see
the center of the galaxy at wavelengths at
your eye detects. So a key to the work that
we've done is to use infrared technology.
So looking at light that is just longward
of what your eye detects. Maybe where a TV
remote control works and that allows us to
see the stars that are at the center of the
galaxy.
And what have you found?
And we found that they go, well. One, that
we can see them, which is rather amazing,
and that they go around the center of the
galaxy quite fast. So my favorite star in
the galaxy, its name is S O 2 goes around
every-
What's its name again?
S O 2. It probably needs a better name.
It's real catchy.
So if you have a better name-
We'll leave it to the audience to figure that
out.
But you can use actually Newton's laws of
physics to show that if you go around every
16 years, um, and you measure the size of
the orbit, which is about the size of our
solar system, that shows that there's about
4 million times the mass of the sun inside
this incredibly small region. And to give
you a sense of the change of our knowledge
or our understanding of what resides at the
center of the galaxy, we've increased the
density of dark matter by a factor of 10 million,
compared to what was known before our work.
So in a sense, we've, we've advanced the case
for the existence of supermassive black holes
by that amount. I mean think about anything
in your life that you'd like more of and being
able to get 10 million times more of, and
that's what's happened at the center of the
galaxy.
So the basic argument as I understand it,
is you're tracking these stars, and their
motion can only be explained if there is a
black hole of that mass residing in the center
of the galaxy.
You're basically weighing this, the what's
at the center.
So is this actual data?
This is data. This is a real thing. So we've
looked at two versions of it. One is the flat
version, which was shown, was playing just
a moment ago and, and it showed my favorite
star. And this is actually a bigger view of
the data that we, that we've taken over the
last., and I can't believe I'm saying this,
25 years.
Have you been involved with it since the beginning?
This is my baby. Oh yeah. Uh, so in fact it's
a, it's interesting to reflect back because
when I first proposed this experiment, when
I first got my job at UCLA, I thought I had
a good idea.
It was actually turned down. They said the
technique wouldn't work and even if it did,
we wouldn't see stars. And even if we saw
stars, we wouldn't see them move. So it was
a lot of no, no no's. And in fact we were
asking to do a project that was only three
years long just to see that stars were moving
fast. No one anticipated that they were moving.
They would move so fast.
How fast is fast? Just to give us a sense-
Oh, um, oh, like 3 million miles an hour,
so they're, they're hauling and, and it's
rather remarkable that we can measure something
on a human timescale. And so as this project
has gone on, and maybe we can talk a little
later about what it takes, um, the technology
has changed so much that it enabled us to
do more and more sophisticated kinds of work.
Um, so this three dimensional animation actually
shows the kinds of stars that we see at the
center of the galaxy. And almost every single
prediction for what we should see near the
black hole is inconsistent with the observations.
What does that mean?
It means it's job security.
You're trying to figure it out.
Yeah.
But, but it's not an inconsistent yet with
say the general relativistic prediction.
No. So there's both the physics side of this
work where you're trying to ask physics questions
like, do supermassive black holes exist? How
does gravity work near a supermassive black
hole? So where we are today is that we can
definitively, or at least in my opinion, we
can definitively say that the supermassive
black hole exists. And then where we are.
Actually we are so in the middle of this.
Can we test Einstein's theory of general relativity?
And that is what you're doing now, if I understand.
Like we're an actually in special time at
this very moment, right?
Yes. We're in such a special moment. I can't
believe I'm actually sitting here as opposed
to being in Hawaii where we take all.
Thank you for taking the time. But tell us,
tell us what's going on.
So the reason I'm so excited and we've been
preparing for this for years, so we've been
doing-
There's no chance you're going to miss this
special moment, but-
Fortunately I have grad students who are on
the case. So we've been using the Keck telescopes,
which are pictured here, for 25 years, and
watching the star that goes around every 16
years. And if you want to test Einstein's
theory of general relativity near a supermassive
black hole with these stars, what you have
to do is first make your first go-around.
That gives you a baseline of what, what part
of space these stars are probing.
And that's 16 years right there.
16 years right there. I can date various moments
in my life around the star. And then what
you want to do is you want to catch it the
next time it goes through closest approach,
and that next time was the year 2018. So I
had been thinking 2018 or bust for a number
of years. So we're in it, we're in the season,
and for us there really is a season because
the earth goes around the sun. So and because
we're looking at infrared light, you're gonna
hear from Shep, there are different kinds
of lights. So Shep doesn't care about the
sun. I care about the sun.
I care about the sun. I'm a sun worshipper.
Because the earth goes around the sun, there's
only a part of the year that we can see the
center of the galaxy at infrared wavelengths.
So for me, we can see it from roughly march
to roughly October. So there was the beginning
of the season and through these roughly six
months, this star is experiencing incredible
accelerations, and is experiencing the most
extreme forms of gravity as it makes its closest
approach. So actually there are three key
moments, one that happened April 10th, one
that happened roughly last week and one that's
happening in September that are going to nail
down this experiment. So it is, um, it's an
exciting moment for us and to see the signal
emerge from the data, it's just a treat to-
So if I understand correctly, so you actually
have a prediction based on the general theory
of relativity, what the trajectory should
be.
Well, here we have to be a little bit careful
because there's a series of kinds of experiments
that you, uh, pardon me, there's a series
of tests of gravity. One is, um, how the,
uh, the light from the star makes it from
the star to us. In other words, how it escapes
the curvature of spacetime. That's actually
the first thing that we're getting at this
summer. The next thing is then how the object
itself moves through space time, which is
actually should emerge over the next few years.
So again, uh, and if you keep going, and of
course that's what we want to do, um, you
can actually measure the spin of the black
hole. So this experiment just keeps getting
better.
Right. And, and it's particularly interesting
I gather because, you know, most people think
that Einstein's general relativity has been
confirmed, but is that the right way of thinking
about it?
Well, it's, you know, it's one of the. Gravity
is one of the four fundamental forces, but
oddly enough, it's the least tested, um, of
those forces. So it's been tested in some
regimes, but it's never been tested near a
supermassive black hole. And in some sense,
a supermassive black hole, or black holes
in general represent the breakdown of the
theory. So what you want to do is you want
to get as close as possible, um, to the point
where you actually know, um, uh, that theory
is no longer holding up. And I think we have
to have today all sorts of pieces of evidence
that says this theory is fraying at the edges.
So we just pushed that frontier forward by
a large amount in a direction that hasn't
been explored before.
So in principle, you could find the first
concrete evidence that we need to go beyond
Einstein's ideas to really describe what's
going on. I mean the best of all worlds, that
would be the outcome of 16 plus years of observation.
Well, the best outcome is actually just figuring
out what's really happening near the black
hole, whatever it is.
Spectacular.
So Shep, you, you were also in the business
of looking at black holes.
There's no business like black hole business.
No business like black hole business. And
uh, so, so you're going about it a different
way. So we're hearing about infrared light
as the probe being used to, uh, in Andrea's
work. You're using what? Radio?
So yeah, we're using radio waves. It turns
out that black holes in a paradox to their
own gravity are some of the brightest things
in the sky, right? And that's because of a
really simple construct, all the mat, all
the gas and the dust is trying to get into
a very small region. So it heats up to hundreds
of billions of degrees around Sagittarius,
a star, the supermassive black hole in the
center of our galaxy. And it radiates in infrared
that Andrea looks at, and also radio waves,
even a little bit in x rays. So if you want
to look at a black hole, you can come at it
from many, many different angles.
Now critical to both of what you're is, you're
not really looking at the black hole, you're
looking at its effect on its environment,
right? So you can't actually see it, per say.
Exactly what happens in the black hole stays
in the black hole. Let's just get that out
of the way right now. But what we do is we
tease around the edges, right? So in that
Cannonball analogy you had before, light was
leaving the black hole, but it also orbits
around the black hole. Just think about that
for a minute. Light orbits something, right?
And it goes around in a circle. And Einstein,
100 years ago, when he came up with this general
theory of relativity, those equations show
that you should see the silhouette of light
around the black hole, and that's because
of these light orbits around. So we look at
it and you see light moving around the black
hole, and it gets brighter on one side.
On the other side you see something that should
be about five times the Schwarzchild radii
across. You know how, how big it should be.
So the event horizon is here and you're looking
at five times that distance.
Exactly, exactly. So you never see inside
the black hole, but you see outside and that
shows us the geometry of spacetime. When you
see something like this, when you see this
shadow feature, you're really looking at the
deepest puncture in space time that we can
imagine.
Right. And is this actual- Have you, is this
what you guys, I mean, can you share with
us what you guys have seen? This is the event
horizon telescope I gather that you're talking
about.
Right. So the so the question is, if you wanted
to zoom in by orders of many, many thousands
and see what was happening right at the edge
of a black hole, you have to go way beyond
where Andrea sees her stars and go much closer
in. Those stars are about a thousand times
farther out than this silhouette that you're
seeing here. And if we can measure the size
of the silhouette and the shape, we test Einstein's
theory of gravity right at the edge of the
black hole, right?
But how are you doing that? There is a handful
of radio telescopes I gather.
So to see something this small, these are
the smallest objects in the known universe,
right? Black holes are tiny, and to see them
you need magnifying power. And as it is with
all telescopes, the bigger the telescope,
the more magnifying power you have. Now we
can't make one huge telescope that sees radio
waves. What we do is we install atomic clocks,
had multiple radio justice around the world.
We record data and then we play it back at
a central facility and we create a virtual
telescope as big as the earth ourselves. These
are some of the people who who work on these
various places.
How many teams are there?
Well, we have eight geographic locations right
now. We're going to nine and then 10 the year
after next. And when you stitch together all
of these telescopes, you wind up getting a
virtual dish that's the size of the earth
that is exactly tuned, it turns out, to image
the supermassive black hole in the center
of our galaxy and we've just taken some of
the first data from this event horizon telescope
one year ago and we're crunching on the data
now.
And what have you, what have you found?
I can't tell you.
Ah, come on!
Now it turns out that if you're, if, if you
really want to make more of these images,
it takes a long time to calibrate the data.
It's all about the details. A lot of people
think that we just turned this telescope on
and we'll see something immediately, but it's,
you know, we're nerds at heart and we just
love to get to the telescopes and find all
these details. And it turns out that you really
have to run down every single one of these
possible sources of contamination of the data,
before you can be sure that you've seen this
kind of shadow silhouette.
Yeah. You know, we were able to actually talk
to a couple members of the team who slipped
us actually some of the data. Hope you don't
mind if we, if we show it here. This is actually,
I'm understanding this is the most precise
image ever of a, of a black hole. Do we have
that? Can we bring the lights down and show
this? Is that, is that doable? Yeah. So, so
yeah. All right there, there, there it is.
Very good. So thank you. That's good enough
for us. Thank you. So, um, so are you going
to look real nervous there for a second? So,
so when will you be releasing? I saw an article
just a couple of days ago, which is kind of
a teaser it seemed like for a release of data
that's coming up. Is that soon?
It'll probably be in the first part of 2019
because right now we're crunching the data.
We know that the Event Horizon Telescope worked.
So what we did was we also looked at quasars—supermassive
black holes that are really far away that
are basically point sources, and everything
seems to have worked perfectly technically
on the telescope, so we know that all the
systems are a go and then we turned all the
telescopes swiveled to look at Sagittarius
A star, the supermassive black hole, in the
center of our galaxy and and we think everything
is working fine there, but we're still crunching
on the data.
So and, and the data. I saw some article that
had come from the South Pole and you had to
wait for the the winter to clear the flight.
Was that the the kind of thing that's going
on, or?
Well, the whole point, as Andrea said, if
you want to test Einstein's theory, you've
got to go to the most extreme points in the
universe. You've got to go to the ultimate
proving ground, which is the edge of a black
hole and we have to go to some pretty extreme
places ourselves, right? So we have teams
that go down to the South Pole, we go to the
tops of extinct volcanoes where there are
radio dishes that do the work that we want
to do. We go to Hawaii, Mauna Kea, High Desert
Plains and Chile, and you go up to these sites
and it's really a bit of a labor of love because
all of these teams go there. They work their
hearts out. They capture data. And this technique
that we use, this Event Horizon Telescope
technique, is really the ultimate and delayed
gratification, right? Because here's what
you do. So when Andrea goes to her telescope,
it's pretty straightforward from conceptually
the light bounces off a paraboloid. It goes
to the focus. That's it, right? You get what
you want right there.
What happens with us is the light hits one
of our dishes, it's stored through high speed
instrumentation we've built over the last
decade on hard disks, the same kind of hard
disk that you would get in your computer and
they stay there until they're brought back
on an airplane because nothing beats the bandwidth
of a 747 filled with [inaudible]. Nothing.
Okay. Even when I'm walking down the hallway
with two of these disks, you know, I'm beating
the fastest Internet in the world. And we
bring them back together. And the operation
in this super computer that we use is equivalent
to light bouncing off of a perfectly shaped
paraboloid joining incoherence, right? So
we play it back together and we adjusted back
and forth until we get it just right. And
that effectively turns the earth into a paraboloid.
If you think about that. So all of this data
has to come back and if it's at the South
Pole, it's in a deep freeze, right? So we've
got to wait six months just to get that data
back. Right? So that's one of the delays that
we've been faced with.
Now you have done some simulations of what
you anticipate emerging from the data looking
at in the magnetic field in the vicinity of
a black hole. Can you take us through some
of the things that you anticipate emerging
from the study? I think we have some things
up.
Sure. So what you're seeing here is the best
guest we have from a high speed simulations
of what you'd see if you had infinite resolution
goggles, right? So you wind up seeing this
shadow feature, the circular feature with
some jets leaving from the north and South
Poles, and that's because there are magnetic
fields right around the boundary of the black
hole. There's relativistic particles, they're
orbiting these magnetic fields and they're
releasing something called synchrotron emission,
which is kind of a characteristic radio emission
you get from these kinds of sources and it's
so bright in that synchrotron emission that
it shines out from the deepest part of the
gravity well, right? So think about it. Everything
has to go right. It's a Goldilocks situation.
You have to be able to see through the earth's
atmosphere, and radio waves can do that. You've
got to be able to see through the distance
between the earth and the galactic center.
Radio waves can through that-
How far is that, just give people a sense.
Oh, it's about 25,000 light years away, right,
so it's, you know, this black hole is not
threatening to us, right? We observe it, it's
nice and so these radio waves can go all the
way to the- From the black hole, but then,
we're not done yet because it has to go through
the hot gas swirling around the black hole.
Right? And then it has to go all the way down
into the gravity well, so it's a Goldilocks
situation because we meet all those criteria
with radio waves and it turns out that the
earth happens to be just the right size so
that when you look at radio waves with a wavelength
of one millimeter, they're perfectly tuned
to take the picture of Sagittarius A star
that
So with an earth size dish it's just the right
amount of resolution.
So sometimes nature throws us all these curve
balls, you know. We can't do this or this
is hard. This is one case where everything's
falling into place, and so we really think
we have a good shot at taking the first image
of a black hole.
And and do you have a chance as well of finding
a deviation from the general theory of relativity?
Can this be viewed as another extreme testing
ground?
What we'll look. It's never a good idea to
bet against Einstein. I don't make it a point
in my career to do it, you know, but it is
a trust-but-verify situation. Okay. I mean
he's a. He was a very smart guy, let's put
it that way, but every theory needs to be
tested.
Well, when you say he's a very smart guy,
that's true, but he wasn't a great fan of
this idea of black holes at all. Right? I
mean he kinda didn't think they were real.
Now he was a little bit off on that one.
Right, so he had one bad moment. But this
really speaks to this kind of golden age that
Andrea was talking about with the Event Horizon
Telescope, with the observations that are
being made by the Keck. We're really in this
discovery space for black holes, and we could
be at the moment when we can start to answer
these questions like do black holes exist?
Was Einstein right at the very black hole
boundary? I mean you showed the Schwarzschild
in the trenches in World War I. Yeah, he died
later that year actually. So this was his
last big discovery and he wrote down the Schwarzschild
metric and he gave the shape of space outside
the black hole and now we're kind of engaging
in this handshake across a hundred years where
we're kind of completing this circuit and
we're saying you made these intense predictions
and we're just at the point now where we might
be able to test them and that is extraordinary.
And, and it speaks to the fact that science
is not linear. We don't go from point a to
point b. We don't say we're going to march
and test this. It's very erratic and that's
why Einstein felt black holes might not exist.
It took 100 years for them to become part
of our lexicon. You know, part of the reality
of our everyday conversation.
Now, do you do, do either of you or both of
you, as you're working on your observational
projects, do you have pet ideas or pet theories
about what the next phase beyond Einstein
might be? Or do you just basically just go
forward into the data and the observations,
and that's the only thing that's really driving
you? Or do you have a, an idea of what might
be the next phase of this understanding a
gravity?
Well, let me just take this for one second.
I'm a real. I'm a realist. I'm kind of a craftsman
at heart. Like I like to go to the tops of
mountains and make observations. I like to
see what's around the black hole, right? I,
I can understand or wrap my brain around the
light that's coming outside the event horizon.
What's inside the event horizon? You know,
that's a question that is hard to even ask,
you know, let alone answering.
Well, you just asked it. It's harder to answer
it.
I did. It's easy to wonder at, you know, but,
but for example, one thing we're looking at
with the Event Horizon Telescope is to see
if that silhouette is not round. What if it's
distorted? Okay. And if it's distorted, then
we have some framework of understanding how
general relativity itself might be violated
to give us those strange shapes. So we're
betting on Einstein, we're betting it's going
to be circular, but if it's not, we have some
ways of understanding what might make it noncircular.
Yep. So we're, we're, we're winding down to
the end of our section, but Andrea, I wanted
to ask you a question which is, how do you
proceed in an era when you might be going
beyond Einstein and when do you know that
you're right? When, when do you know that
things have coalesced to the point that you're
willing to make a statement of that sort?
That's such a interesting and important question
that we're really in the thick of, uh, because
if you see things, uh, that don't make sense,
you, uh, you don't have a context. You're,
you're kind of, you're out there, and you're
exposed, and you have to convince yourself
that what you're seeing is physics as opposed
to experimental error. Uh, so I, I think there's
a, uh, an interesting philosophical point
here about how do you convince yourself, um,
you've got the right answer.
Yeah. I mean there was an interesting case
with BICEP2.
Oh, yes.
A few years ago where some have said that
they so knew what they were looking for, that
they were biased in assessing what the data
was telling them.
It's a classic thing called confirmation bias.
So, and, and this kind of work where we have
such a respect for Einstein and his ideas
that we go in with a premise that it must
be correct. So it is interesting in terms
of how you actually design your teams work
to avoid getting a result you believe to be
true and allowing your team to really trust
what the data's telling you. Uh, so I think
that's a, that's certainly my goal as a scientist
to get to that point where you're really just
listening or paying attention to the information
that might be unexpected, but to try to remove
your, your desire to have any particular answer,
be it Einstein right or be it Einstein wrong.
Yep.
Just to be open to whatever the answer truly
is, right?
Yeah. Well, I should say, you know, all of
us revere Einstein, but at the same time,
how thrilling would it be if either or both
of you find evidence that we do need to go
beyond the insights that he gave us a 100
years ago. So we wish you well and we'll have
you back, a year or two, maybe then you'll
be able to give us some insight into what
you guys have found. So everybody please join
me in thanking Andrea Ghez. Shep Doeleman.
Thank you very much.
