(upbeat music)
(attendees applause)
- Let me thank those individuals
that make these lectures
free for all of us.
Last week I thanked Research
Discovery & Innovation,
the VP for research at
the University of Arizona,
and TEP, they've been the flagship folks
that have been paying for
most of the costs here.
But in addition to that,
there's a list of
individuals and organizations
that have been supporting
this for many years.
And today I'd like to just
point out two of them.
One of them is the Marshall Foundation
and the other one is Holualoa.
Holualoa Investments, the
person that's the president
of Holualoa is Michael Kasser.
I don't know how many of you know Michael.
Michael is incredible.
(attendees applause)
We have a theater in there that I think
in large part is due to Michael's funding.
And not only funding, but pushing hard
for it, I think, to be successful.
He's given money so that
we have amazing athletics
at the University of Arizona.
And he's supported the College of Science
and other entities of the university
with great gusto as he would say.
He believes in arts and sciences greatly.
He is probably the most
extraordinary individual I know.
He knows, like, seven languages
and I hate him for it.
(attendees laughing)
And he got a PhD in chemical engineering
and a master's from Harvard and an MBA.
So anyway, he's one of those individuals
that make you feel small
every time you talk to him.
(attendees laughing)
But not really, because he is always
the same Micheal Kasser
in his Hawaiian shirt.
He is really all Tucson.
And the Marshall Foundation,
many of you have been here for a long time
and know that if you go from Park Avenue
to, let's say Fourth Street and even less,
that place was not very nice 10 years ago.
The Marshall Foundation
has created an environment
around the University of Arizona
that has made it welcoming,
that has supported the
university's mission,
and in addition to that,
supports the university's mission
by giving funds for
fellowships and scholarships
and endowments for faculty.
And I wanna thank both Holualoa
and the Marshall Foundation
for all that they do for
our community, thank you.
(attendees applause)
So today we're in for a treat.
You're gonna hear Feryal Ozel.
Let me just say what my job is about.
I mostly hang around and tell people
that things are all great.
But one of the things that I do
which makes my job really extraordinary is
that when people come to
the University of Arizona
and they apply for a job or we're trying
to bring them to the U of A,
I get to chat with them, more
or less, right off the bat.
And when I met Feryal,
it's one of those things
that you sit there in
front of intelligence
and grace and quality and you go,
holy smokes, if I had
to compete with Feryal
for a job anywhere, I'd be screwed.
(attendees laughing)
That's a scientific term, by the way.
(attendees laughing)
So Feryal is in astronomy.
When I first chatted with Feryal
she was chatting about a job in physics
but she's comfortable in the
field of physics and astronomy.
Astrophysics is probably the
best way of talking about that.
She's an absolute expert in
black holes and neutron stars.
She is wanted by every committee
international that is out there
for her intelligence and for her advice
in where astrophysics should go.
The details of her degrees
are really irrelevant
because you're gonna hear her
today and you're gonna say,
wow, this is something
really extraordinary.
But just so you know that I do know it,
she did get her bachelor's
degree from Columbia.
She got the degree with cuma sum laude.
And she went to Niels Bohr
where she got a master's.
And she got her PhD at Harvard.
She came to us because
we're as good as she is.
(attendees applause and cheering)
And it is time for me to remind you
that every time that
NSF shows the rankings
of the quality of programs,
astronomy always ranks
number one in the country.
(attendees applause)
So Feryal is one of the
reasons why that's the case.
So please welcome Feryal
Ozel who's gonna tell us,
oh, before I do that, because
I think it's important.
It is important to just say the following.
Today's lecture is the
second of what we would
more or less call the scientific method.
The first lecture, for
those of you that were here,
pointed out the importance
of double-blind experiments,
the statistics of doing
work with randomized tests,
and how, in the end, you
can only approach certainty.
I think the lecture was extraordinary
and it very clearly pointed out
the importance of the
generation of statistics.
Now just to make it clear to all of you,
double-blind experiments
and randomized experiments
are not only the purview of biology.
I was talking to my fellow
dean at the College of Science,
Elliott Cheu, who's a particle physicist,
who pointed out that in particle physics
blind experiments had been used
for a long time to get
rid of bias of physicists.
So it comes in all flavors.
(attendees laughing)
But today we're gonna talk about
what in science we call laws.
And even though we may not
know why these laws exist,
these are issues in
science that we can use
to try to understand the parts
of the universe that we cannot see.
And I will leave it at that and I will let
Professor Ozel describe
what she's gonna talk about.
Thank you.
(attendees applause)
- Thank you very much for
that gracious introduction.
Indeed degrees don't matter.
What is fun is exploring the universe,
and that's what I'm hoping
to do with you tonight.
So we're continuing on our journey
on searching for certainty.
Last week, indeed we
heard about experimenting.
And this week I wanna tell you about how,
as astronomers and astrophysicists,
we can say things about
the parts of the universe
that we can't directly see.
But before I tell you
how and are we certain
and what is the search for
certainty, what does it involve,
I wanna begin with a few
facts about our universe.
First is the fact that our observations
with many telescopes in
many different wavelengths
of many different types
of objects have told us
that the universe, by and large,
is occupied by things we don't see.
So to be more precise, we now
say that 68% of the universe
is made up of dark energy.
So when we count up all
the sources of matter
and energy in the universe,
68% of it turns out to be a form of energy
that we don't have
direct understanding of.
This is the energy that makes
our universe expand faster than it should
and we have many different
observations that point to that.
Of the type that is more matter-like,
what we have found out is that 27%,
so about a factor of five
more than normal matter,
is dark matter.
Dark matter is the type of matter
that we can feel through its
gravitational interaction.
It doesn't emit light at all.
In fact, it doesn't have any interactions,
magnetic, electrical, or any other type
of interaction apart from
its gravitational interaction
that we can directly
observe with our telescopes.
Of everything we look at, 5%
or 4.8%, to be more precise,
is things that we have tested.
Meaning stuff that makes up our bodies,
our planets, stars, the
stuff between stars,
gas clouds and anything
else in the universe
that shines and whose light
reaches our telescopes.
Now of this four-and-a-half percent
even among the things that
we say are normal matter
there is a class of objects
that we don't see directly,
and this is the black holes.
So what are black holes?
Well, black holes are
collapsed, dead objects.
They can be formed from collapsed stars
like things that are maybe 20 times
more massive than our sun.
Or they can be at the centers of galaxies.
In fact, when we look around us,
in our galaxy there are
dozens of black holes
that are more like the small type,
what we call stellar mass.
And around us when we look
at each and every galaxy,
at its center there are black holes
whose masses reach 10 billion
times the mass of our sun.
So different types of unseen things,
dark energy, dark matter, black holes.
And I said, let me just begin
with a few facts about the universe.
Now let's stop and take
stock for a second.
How many of you, and please
don't be shy about this,
think that I'm downright crazy?
(attendees laughing)
Show of hands, please.
Okay at least one person is honest.
Okay, how many of you think this is more
like a Star Trek kind of thing?
That I'm not crazy, but
maybe it's science fiction
as opposed to science,
that this is not astronomy?
Okay, there are some who
are admitting to that.
Well, at the very least
when I said all of this
none of you walked out,
at least I couldn't see
anybody walking out.
None of you laughed,
so you probably thought to yourselves,
humm, there must be a
way of knowing things
that we don't see directly,
and she must know that.
Probably that's what you thought.
Indeed, there are some rules of the game.
And we apply these rules pretty diligently
in order to gain an
understanding of the universe,
whether or not light from these objects
reach our telescopes directly.
What I would call rule number
one is the exploration phase.
We do our best to build bigger, better,
and different types of telescopes
in order to look far, in
order to look all over,
and in order to gain all bits and pieces
of information that we can.
We don't just build optical telescopes.
We also build radio telescopes.
We also build X-ray telescopes.
Because there are things in the universe
that are at different temperatures
that shine differently.
We also put telescopes in
orbit around the Earth.
For example, this image
right here is a piece
of what is called the
Hubble ultra deep field.
Meaning this is from the
Hubble space telescope
and it is from a patch
of sky that Hubble stared
at for a very, very long period of time.
And what we saw were
thousands of galaxies.
You might say, humm, how far is this?
Are we really looking as far as we should?
Well, this was a patch of sky
that, to our naked eye,
would look like nothing.
In fact, it was chosen to be one
of the emptiest parts of the sky.
So far away that it would look like
a nothing dot in the
distance, completely empty.
So we are indeed doing our best
in terms of looking far, looking deep
and exploring in every way that we can.
But there is a second
principle that we follow,
which is not exploration,
but it is more about our methodology.
And I would say this
is even more important
than the exploration one.
And I'm going to call
it, do try it at home,
understand how it works, and then apply it
to the other parts of the universe.
So if I can make a table top experiment
in a laboratory and
understand how objects move
or how forces between them behave,
I can for sure apply this
to objects in the sky
or if I can now look at
things in the solar system
and understand how stars
behave in my galaxy,
for sure I can assume, not
just my neighboring galaxy,
but a galaxy halfway across the universe
is also going to behave the same way.
So unlike the usual warning that we hear,
kids, don't try it at home,
we actually do wanna try it at home.
So one of these ideas is that motion
in the universe is deterministic.
I should be able to understand
why a particular phenomenon happened.
I'll give you an example.
Everything that we've done,
every experiment that we've done,
and this is not even a new idea,
in fact, it's one of the pillar
stones of modern science,
tells us that objects
left to their own devices,
travel in a straight line.
If there is no force on them,
no influence of another body
on them in whichever way,
that they will travel in a straight line.
If I now take the same object
and it does this, I know for a fact
that there is another
object that curved its path.
Otherwise it would have
traveled in a straight line.
Do I know exactly what the nature
of the interaction
between this and this is?
Not really, but I can tell
you that there is one.
And in fact, it's even
more powerful than that.
If this is some bright, shiny object
versus something quite dim
that I can't directly see,
I can still tell that it's there.
In fact, this is the whole
idea behind planet nine.
Not Pluto, Pluto is, you
know, it's still demoted.
(attendees laughing)
The real planet nine in our solar system.
Believe it or not, when
we look at the motions
of the outer solar system objects
they are pointing to
the presence of a body,
a planet nine that is most likely
twice the mass of the Earth
and quite far away,
farther than Pluto's orbit
that must be influencing those bodies.
Have we seen it directly? No.
Are we trying to? Yes.
There are now two separate
observational campaigns
searching the outer solar system
mosaicking where we think it should be
and trying to get direct evidence for it.
But this has happened before.
Neptune was predicted before it was seen.
And in fact, it's just the
backbone of our understanding.
So since I talked about the solar system,
let me tell you a little bit more
about how motion in the solar system
forms our understanding
of how gravity works
and how I'm now going to use it
to tell you more about dark matter
and more about black holes.
So this is a view of the solar system
we usually don't have.
We are actually in the plane
with all these orbiting planets
so we get more partial
views of their orbits.
But if we could see it from the top
you would see the inner four planets
orbiting fairly rapidly
and the speed diminishing
as you go farther and farther out.
Now it's the observations
of planetary motion
that started what I would
call physical sciences
or at the very least
observational astronomy
started by understanding how objects
and planets in the solar system move.
So what do you see?
They are moving in nearly circular orbits.
Would an object move around if it was left
to its own devices?
No, there has got to be a central body
that is keeping it in place.
So this was, in fact, it's so monumental
that it is considered to
be the launching point
of the scientific revolution.
It was the Copernican
view of the solar system
that said the sun must be at the center.
This is the first level of understanding
in building a theory.
What I would call an observational model.
Simply finding a pattern
that explains the data.
It might not be quantitative,
it might not be the most
basic understanding,
but certainly putting
the sun at the center
explains all of that.
Now let's look at it a
little bit more closely.
Now the sun is at the center.
But as data accumulated over time
and more and more planetary
orbits were determined,
now scientists could not only look
at where they are but how they are period,
which is amount of time a planet takes
to complete an orbit around the sun
and their distance from the
sun relate to one another.
For circular orbits
this is just the radius,
the distance from the sun.
But in principle, orbits
can be elliptical.
So when we plot these data what we show is
cube of the semi-major axis.
Semi-major axis is the
distance from the sun.
And square of the orbital period.
And these are all the
planets in the solar system.
You see that they lie on a straight line.
So now we are starting to
build empirical evidence,
and this is indeed what now Kepler used
to build his laws of planetary motion.
This is what I would
call the second stage.
I don't understand why the square
of the period is related
to the cube of the radius
or the distance, but I know that they are.
And not just that, but
I know what mass should
be holding these orbits in place.
I know what is holding
these planets in place,
and that is the mass of the sun.
So now simply by plotting these data
on a straight line we can
measure the mass of the sun.
We never have to go with
a scale and weigh it.
(attendees laughing)
I mean, we are, right?
This is going with a scale
and weighing it in a way.
Kepler's laws are really fundamental
in our understanding of the universe.
I'm going to keep coming
back to this again and again.
Now as a mini detour I'm
going to also take you
through the next two stages
which is going from
Kepler to a physical law.
And that we owe to Newton.
Newton was the one who formulated
the specific force on bodies.
And not just that, but
the force between objects
that are interacting through
the gravitational force.
He formulated it.
He said that force is going to be as big
as the two basically that
are applying this force
on each other, separated
by their distance square.
The formula doesn't matter.
But what is very interesting is that
he's now thinking about the interaction
between two bodies, how it
affects each one of them,
and now going from an empirical law
to a physical law.
Oh, I understand where
it's coming for a moment.
So this is also a big
revolution in astronomy.
But are we certain that Newton is right?
Have we now completed
our full understanding
of how we are exploring the universe
and how gravity works?
No, certainly not.
In fact, physical laws
are there to be revised.
In our search for certainty
we get to an understanding
where we can formulate
a physical law, then we make predictions
of how it should work in
situations that we understand.
Go make measurements.
And then they either corroborate
or they refute our theories.
So what happened to Newton?
Well, Newton's laws certainly
work on certain scales.
But they are not there to
be the final word on this.
In fact, they were broken
when Einstein came around.
Now this is Einstein's law of gravity.
It looks nothing like Newton's, right?
So what Einstein said is that actually
all this thing about forces and objects
pulling and pushing on each
other, this is all wrong.
He came up with a completely
different formulation,
a geometrical theory, which
we call general relativity.
He said that masses of all sizes,
even the smallest ones, the black holes,
to entire galaxies warp
the space-time around them
so that other objects that
are simply around them
follow what they think are straight lines
on this warped space-time.
So think of a sheet, four
people holding every corner.
You put a mass at the
center, it bends that sheet.
So now if I take a little
ball and roll it on the sheet
what is it going to do?
It's just going to go and follow
the curvature of that sheet, right?
So Einstein's formulation
is completely different.
Why did he do that?
What was wrong with Newton's laws?
Two things.
One is the practical reason.
Newton's laws worked on
predicting the orbits
of all planets except the
precession of Mercury.
Mercury is the innermost planet.
It is elliptical, and that ellipse rotates
a little bit as time goes on.
Newton's law predicted the precession
but not the right magnitude.
And Einstein knew about this.
But that really wasn't his motivation.
He wasn't trying to fix it
when he came out with this theory.
If he was trying to fix
that he would've added
a little term to Newton's
equation and been like, I'm done.
(attendees laughing)
That's not what he did.
He was actually working in the
patent office in Switzerland
and it was the time when precise clocks
were becoming available in Switzerland
and trains were becoming
more and more common.
He reviewed a lot of
patents for synchronization
of clocks across different train stations.
How do you know that the clock
at this train station in Bern is showing
the same time as in this
train station in Zurich?
He kept thinking about
synchronization of clocks.
He kept thinking about relativity of time.
He formulated his theory
of special relativity
and then he realized that's not compatible
with Newton's law of gravity.
So one of the most fruitful endeavors
we can embark on as scientists is
when we have two well-established theories
and we find a place where
they contradict one another.
That's where we should go.
So physical laws can be
revised in light of new data,
in light of contradicting theories,
and we keep doing that in
our search for certainty.
Let's go back to dark matter, black holes.
I promised you some of that.
And I said we have
tools, we can apply them.
And one of those tools is
going to be Kepler's laws.
So where do we know the
existence of dark matter from?
We know it from what we call
the rotation curves of galaxies.
What does that mean?
There is a type of galaxy
that's commonly seen
in the universe called a spiral galaxy.
So this is a face-on view.
We can see it's not the closest one,
but I like it because you
can see the spiral arms here
and you can also imagine
this galaxy rotating
about its center right here.
And the whole galaxy actually
spins around this axis.
All spiral galaxies do
that without an exception.
So just like planets orbiting
the sun or other stars,
entire galaxies spin
around their own axes.
So this is now our neighbor Andromeda.
It's a slightly more edge-on view.
And I wanna show you
how we actually obtained
these rotation curves.
So this is due to the famous astronomer,
Vera Rubin, of the last century.
One of the things she noticed is
that as we look further and
further out in the galaxy,
so smaller orbits near the center,
larger orbits where the stellar disc ends,
and all the way out here
where there seems to be a lot less matter,
certainly a lot less
light, a lot less stars.
The speeds with which
these objects rotate,
these stars rotate, vary.
So if we make a prediction
using Kepler's laws
about how fast this should turn,
there isn't a lot of mass interior to it,
so it should be pretty slow.
But as you go further and further out
as you get more and more mass holding
all these stars in place, then
the speed should increase.
But as you go farther out,
just like the outer
planets are now rotating
more slowly than the inner planets,
Kepler's laws tell us that
the speed should decrease.
So this red line here is
the Keplerian prediction.
Interestingly, if you are paying attention
to what this Y-axis is,
this is the rotation speed
in kilometers per second.
So the sun is, this is not our galaxy,
but it's about somewhere here
in our own galaxy, the Milky Way,
which also is a spiral galaxy.
So right now as we speak
we are being hurled around
at 200 kilometers per
second; isn't that fun?
(attendees laughing)
Anyway, the numbers don't matter.
What matters is that the
data that they collected
Vera Rubin and her colleague collected
said something completely different.
Indeed the speed increased at first,
but then it stayed there as
if more and more and more
mass was holding this galaxy in place
and allowing it to rotate
with these huge speeds
without breaking apart
or matter flying off.
So very simple application
of Kepler's laws.
Either, option A, I have more
mass there than I can see.
There is some form of matter there
that it's not stars, it's
not gas, it's not dust.
It doesn't shine.
But it is there and I can see it.
I mean, and I can feel it
in the rotation curves.
Keplerian prediction, dark matter.
Or what is option B?
What happened to Newton?
His law was wrong.
So what if now
the galaxy is all there is to it
and this is Kepler and this
is a new law of gravity.
That's possible, right?
We have to weigh both possibilities.
And, in fact, we do.
Just like we have revised even
Einstein's equations over time,
we look for different modifications
that could explain this phenomenon
without resorting to
things that we don't see.
The top equation is
what I showed you first
what Einstein formulated first.
It wasn't his first trial.
He actually tried many different forms.
And at some point he put in an equation
which we now call a termined equation
which we now call the
cosmological constant here.
And then we went on to call
it his biggest blunder.
He said that is absolutely not there.
But now with the accelerated
expansion of the universe
we know that term is there.
The cosmological constant
or something like it exists.
So why stop here?
What if there are other
terms in the equation
that simply weren't discovered before
or that weren't motivated by data before?
This is only one form among
many that I could've written.
So what do we do?
Now we have a framework.
We apply Kepler's laws.
Something's gotta give.
Either there is dark matter
or there is modification
to our law of gravity.
We turn elsewhere.
We say, okay, if it is dark matter
we're going to have to see it in
not just individual galaxies
and their rotation curves
but in clusters of galaxies,
huge bodies in the universe
that contain hundreds of galaxies.
And this is a gallery.
These are all individual clusters.
Some of them named up here.
So what do we do?
We go count up the lights that they have
in terms of everything that emits.
Then we go weigh them
through their gravitational interactions,
and we compare the two.
Is there dark matter or is there not?
There is now overwhelming evidence
that there is far more,
five to one in fact,
more dark matter or more
matter in the universe
than the standard luminous
matter that we're used to.
We didn't stop there.
We started devising experiments to tell
the difference between
the option A, dark matter,
and option B, revised law of gravity.
This is a famous example
called the Bullet Cluster.
We didn't make this happen,
but once we saw that it was there,
and U of A scientists were
involved in this observation,
we certainly knew what to do with it.
This is a very interesting case.
These are now two clusters of galaxies
that have collided with one another.
In fact, they have collided
and have gone past each other.
Dark matter doesn't have any interaction
other than gravitational,
so it can glide through more easily.
Normal matter has other interactions,
electromagnetic, or example.
So it's more viscus.
There is more friction so it moves through
a little bit more slowly.
If this is dark matter,
then what we expect to see is
that more mass should
go through one another
and less light should
go through one another.
Is that what happened?
So this is a Chandra
X-ray image showing you
where the majority of the emitting gas is.
Because they rammed into one another,
this is a shocked gas and there's a lot
of light coming out of here.
Let's compare it to the mass
map of the Bullet Cluster.
The mass is further away.
So there is one center belonging
to the smaller cluster here
and one center belonging
to the bigger cluster here.
So if I now overlay them
you see that most of the
mass has gone farther apart
and the light is interior to it.
Ha, is this the smoking gun?
Is that why we call it the Bullet Cluster?
(attendees laughing)
Not really.
There is a way to explain
this with modified gravity,
but it looks a little bit different
than explaining it with dark matter.
So even though this was a very
big evidence, I would say,
in favor of dark matter,
even this didn't settle the debate.
So the search goes on,
the search for certainty goes on.
And we devised different experiments.
Of course, in the meantime
we also set up experiments
where we can detect dark
matter particles directly.
We look for what it could
be at CERN at the LHC.
We do tabletop experiments.
We do dark matter interactions.
If it has any sort of interaction,
can we see it with other devices.
So that's how we're
going to keep on looking
for more and more and more
evidence for dark matter
and at some point either
be completely convinced
or find an alternative,
which we're happy with.
Switching gears I wanna tell you
about the other unseen in the universe,
which are black holes.
Let me introduce you to one
that I love in particular.
It's the one at the
center of our own galaxy.
It's called Sagittarius A Star
because it's toward the
constellation Sagittarius.
And it was initially discovered
as a radio source in the sky
which is the object right here.
It looks a little bright in this picture
but actually it's kind of wimpy.
It's not a particularly bright source
like we've seen many brighter
sources across our galaxy.
But this is the dead center of our galaxy.
So this is the dynamical center
and this is that radio source.
Now like good scientists
we wanna take a closer look
at the center of our galaxy.
So over time we've
built bigger telescopes,
better technologies like adaptive optics,
and we have gathered lots
and lots and lots of data
on stars that are in the
vicinity of our galactic center.
The star cluster is called S.
I know it is super imaginative.
(attendees laughing)
And the stars are called 101,
102, et cetera, et cetera.
But what I'm going to
show you now is real data,
even though it has been turned
into a time-lapse movie.
These data were collected over 23 years.
The time will be running here.
And each time you see a dot here,
let me run it for you, it is real data.
So these are individual stars
at the center of our galaxy
26000 light years away.
And just like our forefathers,
the early scientists,
followed Mars' orbit and Jupiter's orbit,
we are now following these solar orbits
that are very far away, very dim.
We switched to inferred light
so we can see a little bit farther.
We use adaptive optics.
And at the end you probably saw
that this diligent, repeated observation
of the same field again
and again and again
to trace out the orbits have given us
two very fruitful results,
which is that the closest
two stars have completed
a full orbit over these 23 years.
What are they orbiting?
Humm, I don't know.
I don't see anything, do you?
But maybe, just maybe
by using their orbits
I can get some information about how big
the thing they're orbiting is.
What would I use? Any ideas?
Kepler's laws?
Yeah, Kepler's laws.
I know if something is
orbiting something else
how big the mass should
be that holds it in place.
Okay, it is 4 million
times the mass of the sun,
what is holding these orbits in place,
and yet these orbits are tiny.
And they are very far away.
But if the object that is 4 million times
the mass of the sun was anything like
normal stars that we see,
that object would shine
brighter than our sun.
And I don't mean at the
distance of the sun.
I mean from the center of our galaxy
it would look brighter.
It would overwhelm the amount of light
that we get from our own sun.
Certainly that's not happening.
Instead it's a relatively
wimpy radio source.
So are we convinced, yay, black holes?
Certainly a lot of mass.
It's not shining; it looks black.
And Einstein's theory
predicts the existence
of these objects that collapse to nothing
at the end of their lives.
So are we done? Not really.
Because we are searching for certainty
we actually go the next step.
If these are black holes,
not only should they contain
a lot of mass in a small
volume and look dark,
but they should have a
very peculiar property
called an event horizon.
It is the point of no return.
That's basically the
definition of a black hole.
Not every massive object
that is not emitting
a lot of light is a black hole.
It needs to be compact enough,
its gravitational pull on its environment
should be strong enough
that at some distance
from the black hole, even
light cannot make it out.
So there is a complete absorption
of light to the interior.
Therefore, the center of such
a thing should look black.
This is an animation that's showing you
what would happen if I was
shining light on a black hole.
If the light's rays were sufficiently far
from the black hole, they would be bent
a little bit, just like those motions
in the bent space-time, the fabric.
But they would go on their way.
If they are coming too
close, see what happens?
They get bent so much that they end up
in the circle of no return
and that leaves that signature
that should be the
signature of the black hole.
Now this is the very basics of the theory.
But we want to put this into practice.
We wanna see if black holes have horizons.
So what we discovered in the recent years,
well, not that recent.
I was actually doing my PhD
when I first calculated this.
But not only horizons should exist,
but with the right wavelength of light
we should be able to see them.
So what I calculated,
this is in year 2000,
is that if you look at
long radio wavelengths
there is a lot of opaque
material around the black hole.
But if you start looking at
shorter and shorter wavelengths
at around a millimeter
that gas turns transparent
and the hole in the middle should appear.
So if we could take an actual
picture of a black hole,
not in visible wavelengths,
but at one millimeter,
our theories predict
that, A, we should be able
to see down to the horizon and, two,
if it is a black hole
with an event horizon,
there should be a hole in that image.
This is year 2000.
Since then, we've built
many, many different
sophisticated computer simulations
of black holes and their environments
trying to understand
how black holes behave,
how the gas around it behaves.
So as gas gets trapped in this well,
potential well going
down to the black hole,
for a while it heats up and it emits light
and that light is able to get away.
We've built computer models of exactly
how this light shines,
how much of it can we see.
And this right here is a compilation
from many groups around the world,
six different types of simulations,
six different types of
algorithms, physical models.
And these are all very
expensive simulations.
Each one of them has been
run on a supercomputer.
Upper left one is ours right here
at the U of A, my group's work.
And you can see many
different predictions.
Why is this important?
It's important because if we're going
to go on this huge fishing expedition,
taking a picture of a black hole
and seeing if it has a hole in the center,
we wanna know what we're looking for.
We wanna be able to interpret our data.
We didn't stop at this at the U of A using
our computer cluster, El-Gato,
which was supported by the
National Science Foundation
as well as the VPR's office.
We looked at how this image
could change over time.
So not just the still,
but if we did subsequent
shots of images of the black hole
at the center of our galaxy
or in nearby galaxies like in M87,
we basically made movies of
how these images would change.
These are our predictions.
It turns out that predicting something
and actually measuring it turns
out to be quite different,
especially in this case.
Because the images that we were predicting
turned out to be so small in the sky
that it would be the equivalent
of putting a doughnut on the moon
and asking us to take a picture of it
with cameras from here on Earth.
Literally the size of a doughnut
at the distance of the moon.
It also turns out that the telescope
that has sufficient resolution
to carry out this experiment
is as big as the Earth.
(attendees laughing)
We went to funding agencies.
We said can we build a big telescope.
(attendees laughing)
They said no.
No, we didn't, we didn't even try.
But we said, humm, okay,
given we can't build
a telescope literally as big as the Earth,
how about figuratively
as big as the Earth?
And that is a concept
called interferometry.
What you do is you put a telescope here.
You put a telescope there.
You look at the sky at the same time.
You record the data.
You record it very faithfully.
Time-tag it so you know exactly
when your signal arrived.
Then you bring these two
data pieces together.
You combine it.
And it is as if you looked at the source
with a telescope as big as the
separation between the two.
In terms of collecting power,
of course you don't have it.
Your dish is your dish.
But in terms of angular resolution,
how big a telescope you have,
how fine a scale you
can resolve in the sky,
it serves that purpose.
So this is just a
graphic that explains it.
If I want to take a
picture of this black hole
I put one radio telescope here.
Remember millimeter is the magic number,
millimeter wavelength of light.
I put one here.
Light arrives at these telescopes
at slightly different times.
I record it, and then I
correlate it after the fact.
And hopefully I have an image
that looks like a hole in the sky.
Or looks like one of those images
from the image library that I showed you
just a couple of minutes ago.
We've been working on
this for about 15 years.
We've been working on
building a global telescope,
what we call an Earth-sized array.
For those of you who were in my talk
a couple of years ago,
maybe you heard some
of the ongoing efforts
in building this array.
And we were just getting ready in 2017
to make the first round of observations
that involved all these
telescopes across the globe.
What did we do?
Well, we're using our own
telescope on Mount Graham, SMT.
And this year actually we're working
on putting a second dish on Kitt Peak.
So this year's observations are going
to have two Arizona telescopes.
We also outfitted the
telescope in the South Pole
so we can literally span
the size of the Earth.
This is the Greenland telescope,
our northernmost point and
our southernmost point.
Two in the Atacama Desert
in Chile, ALMA and APEX.
ALMA itself is an array.
It's a big, powerful telescope
that we are lucky enough
to use for this experiment.
And a bunch of others, LMT in Mexico
is a very important site.
You can see how it's connected
to all these other sites so we can have
all these pairs that are
connecting the information
and giving us more and more of that image
that we are looking for.
This took many years.
And it took a lot of effort.
So just one of those that I really like,
my colleague, Dan Maroney,
here at the University of Arizona.
This is from one of his
trips to the South Pole.
He's actually there right now
with two of his graduate students.
This is a couple years ago.
This is the South Pole telescope.
And on a sunny, wonderfully warm day
what they did was put this receiver,
you can barely make it out in purple,
in to the telescope so that they were able
to record the right kind of data
and do this experiment.
You might also see his grad
student right here, Johann.
(attendees laughing)
It is so much fun to be a
graduate student in our department.
(attendees laughing)
It took years of effort.
So for those of you who were
at the lecture last week,
Joanna talked about
these controlled trials
and double-blind experiments.
In astronomy we don't have the luxury
of controlling the phenomena,
but we certainly have the luxury
of designing our experiments.
Here is my prediction.
Here is the right place to look,
the right type of data to get,
and if it's option A, I will know.
And if it's option B, I will know.
So it's certainly an experimental science,
not just an observational science.
When you spend so much time
building the right type
of telescopes, equipment, experiments
in order to answer questions.
In 2017 we did our first
full array observations
even though the array
keeps growing, like I said,
Kitt Peak is coming online this year.
What we mean by full array is having
both the east, west, and the north, south
large coverage that will
give us enough resolution.
And you can see from the happy faces
in these pictures that weather was good
on seven different sites.
And we need good weather
because millimeter
wavelength gets absorbed
by moisture in the atmosphere.
We were lucky enough to
get five nights of data.
And at least I'm bringing you up to speed
a little bit on what happened
in the intervening two years.
This is April of 2017.
We collected three-and-a-half
petabytes of data
over those five nights.
It's an extraordinary amount.
And since then what have we been doing?
Well, first, we literally had
to physically ship the data
because it's so much data
that you can't actually
transfer it over the internet
from location A to location B.
Remember we now have to collect
all of these data centrally
from the South Pole, from Greenland,
from everywhere and combine it
and search for where they match up.
It's so much data, FedEx took
it to different places for us.
(attendees laughing)
So these are some of those hard drives
being crated and being shipped.
And this is one of the
correlation centers,
one of the two correlation centers
with disc after disc after disc of data.
We did combine it.
We calibrated it.
We wanted to make sure that each telescope
behaved as we expected,
that it didn't get too little light
for whatever technical problem.
That calibration step is very important.
And in the intervening year-and-a-half
we've been working super hard
on interpreting the data.
So as I said, correlate,
calibrate, interpret.
And we are very close,
unfortunately I won't be able to show you
what we see tonight, but we are close.
I can tell you that later this spring
we will be able to release
our first set of data
with some results about black holes
and what their environments look like.
So I'm excited about that,
but I'm just going to leave you with this.
My daughter is here in
the audience tonight
and she can tell you
the past year-and-a-half
is looking like more and more
like searching for serenity
as in let's just be done with this.
I'm working around the clock
as opposed to searching for certainty.
But really the question is
do black holes look
anything like we predicted?
Is it going to be one of these images?
Is it going to be anything
that is similar to it?
Is Einstein right in this
particular prediction
or is there a place where Einstein's
theory of gravity also breaks down
because it's incompatible
with our understanding
of the microscopic world?
Hopefully we'll find something interesting
that I can share with you.
But I have to say,
failing is not a bad option
because it's job security.
(attendees laughing)
If we say we understand
everything about the universe
let's go home, that is
not going to be fun.
So we're just gonna keep on searching
for more and more
evidence for our theories
and hopefully some will fail, thank you.
(attendees applause)
