>>Female Presenter: Good afternoon everyone.
Thank you for your patience today.
Today's guest at Authors at Google New York
is Caleb Scharf, who is the director of Columbia
Astrobiology Center.
He writes “Life, Unbounded” Blog for Scientific
American and has written for New Scientist,
Science and Nature among other publications.
Let's see, he is, has served as a keynote
speaker for the American Museum of Natural
History and the Rubin Museum of Art and is
the author of 'Extrasolar Planets and Astrobiology'
and the winner of the 2011 Chambliss Astronomical
Writing Award.
Ladies and gentlemen, Caleb Scharf.
[Applause]
>>Caleb Scharf: Thank you very much.
Oooh.
Wow.
[Laughs]
>>Caleb Scharf: I guess it's loud enough.
Thanks.
So I'm gonna talk to you a little bit today
about a story.
And it's a story related in this book and
I'm gonna give you a little piece of that
story today.
And it's really a story about strange things
in astrophysics and the universe around us.
And, in particular, it's about how some of
the most bizarre and fantastical phenomena
in the universe turn out to be surprisingly
important.
Turn out to be things that matter, conceivably
to us.
They turn out to have a strong influence on
the particular cosmic environment that we
find ourselves in.
And I think it's, this story in particular
is somewhat unusual.
Oh, there's two mics, that's why it's louder
here.
[Laughter]
>>Caleb Scharf: And as much as, this all begins
with a theoretical conception that happened
more than 200 years ago.
It was a pretty outlandish theoretical conception
200 years ago and it remained so until really,
very recently.
So let me tell you a little bit about this
today and I'll try to keep this to the 45
minutes and then if anyone has extra questions
I have some extra slides at the end.
The story begins here.
Not really the place you'd expect a story
of astrophysics and cosmology to begin.
This is a Michael's Parish Church in West
Yorkshire in England and the reason the story
begins here is because of this guy, [clears
throat] Reverend John Mitchell.
So John Mitchell was a very interesting character.
We know a certain amount about him but not
as many details as we should for someone of
his stature.
Because before John Mitchell was the Reverend
John Mitchell running this little church in
England he was actually a renowned scientist
at the University of Cambridge in England.
And this is back in the 1700s.
He was one of the people who founded modern
seismology, for example.
He's also someone who, together with Henry
Cavendish, created a special type of balance
that enabled them to make the first accurate
measurement of the Earth's gravitational field,
gravitational acceleration at the surface
of the earth and, therefore, deduce the mass
of the earth or the weight of the earth.
Why he ended up as a Reverend, we don't actually
really know.
Perhaps this was a more stable, better paying
job than being an academic at Cambridge.
[chuckles] That's true, a lot of human history
to be in the church you were probably better
off than doing other things.
Now Mitchell, while he was Reverend of this
church, got interested in other things.
He got interested in astronomy.
And one of the things he became particularly
fascinated with, was the idea that objects
like stars could imprint something about themselves
on the light that came to us from them.
Now this sound, if you are at all familiar
with modern astronomy that sounds trivial,
of course that's true.
But at the time this was quite a revolutionary
concept.
And he gave a presentation in 1783 at the
Royal Society in England where he discussed
these ideas.
And, in particular, he discussed the idea
that he had based on Newton's physics which
was that if a star has gravity and if light,
as this is the way people thought about light
at the time, if light is slowed down by the
effect of gravity, in other words people were
thinking about light just as you think about
throwing tennis balls or baseballs, particles
of light would get slowed down by gravity.
I know this isn't the case but at the time
they didn't know this.
He made the suggestion that well, stars are
big, that gravity ought to slow light down.
[Clears throat]
>>Caleb Scharf: So, if we could measure the
velocity of light that was being emitted by
stars towards us we would have a measurement
of the star's mass.
It was a very clever idea.
It wasn't quite right but it was very clever.
What was really brilliant was that he took
this to the extreme.
He said, "Well, what happens if you have a
star so massive, so enormous that it slows
light all the way down to a stop?"
So Mitchell actually came up with an idea
that was later called "the dark star."
So he suggested, and this is a small quote
from what he said at this meeting in 1783,
a truly enormous star, perhaps 500 times the
size of the sun, would be so big that it could
slow down light altogether to a stop and you
would never actually see that star.
It would drop out of view.
Now, this was very, very interesting except
nobody paid any attention for another 100
plus years.
What happened then was Einstein.
And this is a very crude overview of Einstein's
general relativity.
I'm sure some of you are much more familiar
with this than I am.
Einstein came along and, in 1915, he produced
his general theory of relativity.
So what Einstein realized was that what we
had thought of as gravity wasn't quite right.
Gravity is really a consequence of what mass
does to space around it.
Mass distorts space and time around it.
A very common way of thinking about this,
and it's not a bad analogy, is to think of
a rubber sheet, and I'm sure you've heard
this, this is a very, you know, I couldn't
think of a more exciting analogy that worked
as well so I'll use it, it's a very old analogy.
Think of a rubber sheet representing space,
three dimensions of space collapsed to two
dimensions.
If you put a weight in that rubber sheet it
will distort, it will bend down.
And Einstein realized that this was a more
accurate description of what mass does to
space around it and that gravity is simply
a consequence of objects trying to follow
the shortest path in this distorted space
in time.
The mass pulls space around it.
It bunches it up around itself and it stretches
it down towards itself.
This is just a silly little illustration to
show that.
Now with space it's stiff but flexible.
It actually takes an awful lot of mass concentrated
into a very small region to make an appreciable
distortion in space.
And at the same time Einstein produced his
theory of general relativity, almost immediately
it came out, people started applying it.
And one of the first applications was made
by someone called Karl Schwarzschild, he actually
did this from the Russian front, he was in
the German army in World War One and I guess
this was a good distraction.
He used Einstein's relativity to produce equations
describing what would happen around the simplest
sort of object you could imagine, a sphere
of mass.
And Schwarzschild sent these solutions to
Einstein and it became apparent in these solutions
that you could have extreme versions of space
distortion.
If you pack enough mass into a small enough
volume, if you make it dense enough, it will
pull space inwards, distort it to such an
extent that ultimately, that object can create
what we call an event horizon around itself.
An event horizon is simply a place where the
curvature of space, the distortion of space,
is so extreme that light itself can't escape
from there.
Now, this stage, everyone knew that light
had the same velocity no matter what.
So the event horizon is all about stretching.
If you try to have, or if light tries to escape
from within this event horizon it is stretched
to such an extent that you never see it in
the external universe.
Now there are all sorts of other fascinating
aspects to this but I'm gonna skip most of
those and focus on something very particular.
So here was Mitchell's idea again but there
could be objects that were so massive, in
this case so massive and so dense, that they
would essentially vanish from view.
They would drop out of normal existence.
'Cause light is the ultimate measuring tool
and, so, if light can't escape nothing else
can either.
Also other things happen when event horizon
time slows down, for external observers and
so on.
So it's a very interesting concept and it
was a very theoretical concept.
Einstein hated it; in fact, Einstein did not
like this idea.
He felt like it was nonsensical.
The universe couldn't conceivably, actually
make such objects.
Yes, the equation said you could but there
was no way the universe could do this.
Let me just show you a little movie just to
illustrate this most simple of all event horizons,
what became known as black holes.
Mitchell's dark stars transformed into black
holes.
That's a whole other story as well but involves
a great deal of scientific work to convince
everyone these things could be real.
So here's a little movie just for fun and
it's, it's, it's accurate, scientifically
accurate.
What you'll see is a small journey into a
black hole and you'll see the event horizon
as a dark object and there's a red grid on
it.
That red grid is purely for artistic effect
just to show you the distortion of light.
Because what a black hole does more than anything
else in the universe is distort light around
it.
It acts a bit like a lens.
So you'll see light in all sorts of peculiar
circular patterns around this object and it's
because the light is being wrapped around
and around close to the event horizon before
it gets to you.
So you actually see multiple images of what's
behind us.
Let me just set that in motion.
And it's really just to give you a feeling
for this.
What you'll see, you'll begin to see this
grid black hole.
And you'll notice, you can see both North
and South Poles of the event horizons cause
the light is bent around.
So there's no place to hide around a black
hole.
You will be seen no matter where you are cause
the light coming from you will get bent around.
Now, pretty soon it's gonna hit, it's actually
gonna go in to, it's getting toward the photosphere
where light can actually orbit the black hole.
Now it's gonna hit the event horizon in a
moment.
Boom, there it goes into the event horizon
and the universe becomes extremely distorted
if you are looking out from that position.
Okay, that's fun.
This is good stuff.
This is, sort of, you know, what you'd see
in science fiction and so on and there have
been many things written about the peculiar
way in which your perception of the world
would change if you dropped into a black hole.
These objects are extremely compact.
These objects would have to be extremely compact
to distort space and time as much.
I just show you three, a couple of quick slides
just to illustrate that cause it's important
for what I'm gonna show you next about the
real universe.
The size of black hole event horizons, so
I picked this for a personal reason but it's
a small island off the coast of Europe.
[Laughter]
>>Caleb Scharf: And what is interesting is
that the event horizon that the object creates
around itself is actually extremely small
and it's because space time gets distorted
to such an extent.
So a black hole, an object containing ten
times the mass of our sun, squeezed inside
its event horizon, would only be 37 miles
across, so it'd actually just block out London
and the main road, the main highway that goes
around London which is called the M25 and
if you've ever been on the M25 the idea of
time slowing down at the event horizon is
writ large.
[Laughter]
>>Caleb Scharf: Maybe some of you have or
it could be the beltway around D.C. as well.
So a ten solar mass black hole is an astrophysically
plausible object but it would only be 37 miles
across, event horizon would only be 37 miles
across.
Let me just show you a couple more examples.
And, again, this is relevant to what I'll
show you next.
Let's go a bit bigger, what about 100,000
suns, I mean I haven't told you that these
things exist but let's just do it anyway.
Well, 100,000 suns packed into an event horizon
would fit easily inside our sun.
These are extraordinarily compact and dense
objects.
If we go up in scale a little bit it's not
a particularly pretty picture.
Something 4 million times the mass of the
sun, there's a reason I'm using 4 million
times mass the sun as you'll see momentarily.
Something that size, the event horizon would
fit easily inside the orbit of Mercury.
So on an astrophysical scale these things
are tiny given the amount of matter.
One last one, what about a billion times the
mass of the sun?
Well we, oops, sorry, an object a billion
times mass of the sun would have an event
horizon that fits readily within the orbit
of Neptune in our solar system.
Again, extraordinarily compact and that's
an important thing to remember.
So, we now know these things are real, at
least we're 99.9, maybe 9, percent certainty.
And, in fact, the best example is the most
convincing examples are, indeed, these things
that are millions to billions of times the
mass of our sun.
Let me show you one of the clearest pieces
of evidence.
So what I'm gonna play for you is a tiny little
movie, a time lapse movie over a number of
years, of the motion of stars at the very
center of our galaxy, the Milky Way.
Now this is being cleaned up but what you
see is an accurate representation of the motion
of these stars and their relative brightnesses.
So let me just run that, runs a little bit
then it zooms in.
And you'll see things are kind of wiggling
around in the middle and you'll see one thing
gets a little bit of a kick.
There it goes.
Okay, lets zoom in on that.
You can see the scale here; we're looking
at a region of space, maybe 10 to 15 light
days across.
Now there's a star in the middle of our galaxy
that has this rather dramatic orbit.
It's dramatic because the point where it is
closest to something in the middle, can't
really see what's there, in fact it's very
hard to see what's there even with the best
telescopes, there isn't much light coming
from that apparent center point for these
orbits.
The closest point to that center, this star
at its fastest motion in the orbit is moving
at about 3,700 kilometers a second.
Just for comparison Mercury goes around the
sun at about 60 kilometers a second.
What this tells us is that there is an enormous
mass packed into a tiny region from the very
center of our galaxy.
If you do the numbers you find that it's about
4 million times the mass of our sun.
We now think that this is a super massive
black hole living in the center of our galaxy
which is interesting and we'll come back to
that.
That's not the only way we can spot these
things now.
In fact, the most common way that we see signs
of black holes in the universe is because
they're not black at all or at least what's
going on around them is not black.
When you drop matter into a black hole, it
gets torn apart, it gets shredded and it gets
accelerated and you can do it in all sorts
of different ways and you get the same outcome.
Dropping something into a black hole means
it will accelerate eventually to close to
the speed of light.
That's before it reaches the event horizon.
So if anything happens to it along the way,
if it collides with something else, energy
can be released.
The analogy I like to use is water going down
the plug hole in your bathtub and often it
makes noise, it gurgles, right?
It's essentially the same process.
The gurgling is the energy of motion that
the water, as it swirls around, being converted
into sound waves that bounce back out into
the room, okay.
It's kind of the same thing that happens around
black holes, right, but on a much, much grander
scale.
So matter falling into black holes doesn't
go quietly.
That energy that it can produce in the form
of light, in the form of subatomic particles
cause you're tearing stuff apart and accelerating
it, spews back out into the universe.
So a more realistic look at what happens as
you fall towards a black hole is represented
in this short movie.
And I should say one other thing, most black
holes have spin.
Okay, just like anything else, like a planet,
like a star, black holes spin.
Now it's a very weird thing because you can't
really see the black hole, you just have this
event horizon.
But because they have distorted space so much
they actually drag it around with them as
they spin.
Like having a thick rug and you're pulling
it around, so the very geometry of space gets
pulled around with the spin of a black hole
and that means it is impossible to stand still
around a spinning black hole.
So this just ramps up the acceleration of
matter that falls into a black hole.
Black holes can actually have an electrical
charge and this gets very complex, one of
the most complex aspects of black holes but
it means that you can have additional mechanisms
that can accelerate matter.
It's like having the large Hadron Collider
in a natural form except stuff doesn't just
go around in a ring, it can jet out.
So let me just show you this movie and this
was, again, reasonably, as far as we know,
a quite accurate representation.
Now we're falling into a spinning charged
black hole that has matter around it, matter
that is, itself, falling in, getting accelerated,
getting torn apart and some of that energy
of motion is being converted to other forms
as the matter sort of gurgles down the drain.
So, you can see the spinning black hole, you
see matter spinning around and it's also there
are jets or streams of accelerated particles
leaving from just outside the event horizon
and shooting back out into the universe.
They're so accelerated that even gravity of
the black hole, outside the event horizon,
doesn't really slow them down very much.
So that's a theoretical picture, I'll just
let it run a little bit, though all it does
is get very, very bright and then it stops.
In the real universe we see this all over
the place.
Let me put up a few images here.
This is just a small selection of maps made
using radio telescopes that had targeted precisely
this sort of situation.
You can probably see in some of these images,
and I'll show you more in a moment, that they're
tiny little bright specs and then there are
these red like streams or jets coming out
of them that then seemingly crash into something
in the intergalactic space and turn into these
great lobes of particles.
What we're looking at is the cooling of electrons
that have been accelerated around super massive
black holes, just like a particle accelerator.
As they cool down they emit radio waves and
radio admission.
The size of these structures, again I'll illustrate
this a little bit more, but they're between
a few 10s of thousands of light years across
hundreds of thousands of light years across.
They're absolutely enormous.
To cut a very long story short, we now realize
that black holes that have matter falling
into them are actually capable of the most
efficient conversion of matter to energy in
the universe.
You can produce energy this way even better
than nuclear fusion.
In fact, in optimal cases it can be 50 times
more efficient at getting energy out of a
certain amount of matter than the equivalent
nuclear fusion.
It's just gravity.
Gravity is really potent and black holes,
because of their nature, are like a turbo
charged version of a normal gravity well.
So this raises all sorts of interesting questions
Where's all this energy being produced by
black holes.
They're not hiding away at all.
Now they don't, not all black holes are in
this situation but a large number of them
are and across cosmic time, across the last
13.8 billion years, this kind of thing has
gone on a lot.
To show you a couple more examples, this is
particularly beautiful example, this is the
galaxy called M87, it's not too far away from
us.
Now what you see here is this great yellowish,
greenish haze, or actually the stars of the
galaxy.
You can't distinguish individual stars because
there are probably a few hundred billion stars
there and in the very center of this galaxy,
there is supermassive black hole eating matter,
eating gas, eating stars, eating stuff and
it's generating one of these streams, one
of these jets of accelerated particles and
you can see it glowing.
And it's glowing in ultraviolet light, and
again, it's these electrons being accelerated
and being shot across intergalactic space
going to stellar space and this structure
is a few 10s of thousands of light years across.
They're really quite remarkable cause it looks
kind of tiny, right?
It looks like the sort of thing you might
see under a microscope but it's not that at
all.
There's another example and it's just to show
you some pretty pictures.
It's always one of the beauties of astronomy
as you have pretty pictures to show.
This is a galaxy called Centaurus A and not
too far from us, it's kind of a messy galaxy
but I think you can see that on top and bottom
there's sort of strange plumes coming out
and there are two, there's a supermassive
black hole deep inside this galaxy, And, in
fact, we've discovered, the Milky Way is not
alone in having a supermassive black hole
in its center.
Pretty much every galaxy in the universe has
some kind of supermassive black hole in the
center, some of them even have more than one
which is another story but that's just to
tell you.
Just to get back to this notion of scale,
cause I think it's very interesting and it's
quite astonishing, here's another galaxy.
It doesn't look very interesting, it's about
600, yes, it's about 600 million light years
from us, it's called Cygnus A, this is a Hubble
space telescope image of it in visible light.
It's kind of, it's a little distorted, mucky
looking thing.
But let's put it in context, shrink it down,
now let's put that map of the stuff coming
from the black hole up.
So I think you can see the black hole in the
center is producing a pretty big structure.
That structure, end to end, is about 500,000
light years across.
It vastly outreaches the size of the stars
and the galaxy, the visible part of the galaxy.
And remember the black hole itself, this one
is about a billion or so solar masses would
fit readily inside our solar system.
This galaxy probably has a hundred billion
solar systems in it so it's a tiny, tiny thing,
it's like a bacterium suddenly inflating a
balloon the size of Manhattan.
So, as we've learned more about this it's
raised a number of questions and a very interesting
question has been does this energy do anything
other than just make these extraordinary and
beautiful and majestic structures in the universe?
And this is something that we've really learned
a great deal about in the last 10 to 15 years.
And what we've learned is starting to revolutionize
our vision of, not just black holes, but how
our whole universe comes to be the way it
is, how it evolves, how it changes with time.
Let me just say a little bit about that.
This is another galaxy and I'm showing you
this because it's one of those places every
so often something comes a long and it's like
finding that rare species that suddenly illuminates
the whole tree of life.
You go, "Ah, that's what it is."
We've had this question, "How does energy
relate to everything that we see?
What does it do?
Okay, black holes are spewing energy out of
the universe, what does it do?"
Well, this is one great example that really,
for many people in this field, pinned it down
a number of years ago.
This is another galaxy, this is a galaxy called
Perseus A; it's about 250 million light years
from us.
Doesn't look too unusual, looked a little
messy, Perseus A is, like many galaxies, part
of a greater collection of galaxies.
Galaxies tend to come in what we call clusters.
So Perseus A is actually in a system of a
few hundred to a few thousand other galaxies
that are all sort of gathered together across
a ten million light year region.
And in these situations, these are kind of
the mountains in the distribution of stuff
in our universe.
In these places the galaxies are typically
surrounded by very hot gas, gas between the
galaxies, it's like an atmosphere surrounding
them.
It's very, very tenuous, to us it would be
like vacuum but on these large scales it's
quite substantial.
And this gas is very, very hot and you can
see it because it cools down by admitting
x-rays.
It's just a hot version of things, it's hotter
than your typical incandescent lamp and so
the energy admitted by the atoms in it tends
to be in the x-ray part of the spectrum.
We can make a map with that x-ray light and
kind of see the atmosphere surrounding all
of these galaxies at once.
It's a really neat trick to be able to do.
Luckily, we now have instruments that can
do this.
So let me show you that x-ray map, okay, it
may look a little odd to start with so I'm
gonna explain what's going on here cause this
is, I hesitate to call it a Rosetta Stone
but it definitely was something when we saw
it, it kind of changed everyone's view.
So the galaxy is in the middle here, you can't
really see it because we're looking at x-ray
light.
What you can see is that this hot atmosphere
surrounding these galaxies is far from uniform,
there's all sorts of interesting structure
in here.
There is a supermassive black hole in the
center of that galaxy, Perseus A, and it's
doing what all the others tend to do when
they get fed, it's shooting out jets of material
and great clouds of subatomic particles.
Except in this case cause it's inside the
structure.
You see these darker regions, there are a
few dark patches some of them even far out,
those are bubbles.
Those are literally bubbles inflating these
holes inside this atmosphere just as if you've
taken a straw and put it in a milkshake, right,
like annoying people do, well, my children
do and the highly energetic material coming
from around the black hole literally inflates
bubbles in this atmosphere and the bubbles
are buoyant.
This is a gravitational system so it's just
like a bubble in a milkshake or a bubble in
the ocean floats up.
And you can see that there are darker patches,
there's one in the upper right hand side there
that's floating up through this atmosphere.
It's on a scale of hundreds of thousands of
light years and the time scale of which the
black hole burps these things out is on a
similar scale, a hundred thousand years, maybe
a million years.
Every time it gets fed it does this.
You may be able to see something else in here
and I should say this gas, okay, what this
gas really wants to do is cool down and make
new galaxies and make new stars.
It's trying to do that but the black hole
is disrupting it.
You may be able to see, it's always hard with
this image, I try not to manipulate it too
much but there are sort of ripples in this
image, concentric ripples coming from the
center, very subtle features.
Those ripples are sound waves that are set
in motion by these bubbles.
The sound waves spread out across the whole
system.
The sound waves, peak to peak, are maybe a
hundred thousand light years.
So the pitch of these sound waves is about
57 octaves below human hearing.
A very deep note being played by a black hole
and the power being output in the sound wave,
the power being converted into these sound
waves, a trillion, trillion, trillion watts
roughly, 10 to the 37 watts.
Okay, and that's being propagated out across
about a million years, light years, of space.
That energy is helping moderate what this
atmosphere does; it's actually helping prevent
this gas from turning into new stars and galaxies.
What this means is that, and this happens,
actually, in more than 70 percent of structures
like this.
You can find a cluster of galaxies anywhere
in the universe you'll see this happening
more often than not.
So this really convinced many of us that supermassive
black holes are playing a very important role
in regulating the way in which the universe
makes stars and makes galaxies.
But this is still relatively nearby so the
question was, "Is this happening early on?"
If it's happening early on then it means that
black holes and the galaxies and stars have
this intimate relationship that we hadn't
previously understood.
Well, it turns out that it does.
And I have to show you this cause it's one
of my favorite things.
This is the work I did so I have to show you,
I'm very proud of it cause it really, for
me at least, convinced me, it doesn't look
very impressive but it maybe it will be once
I tell you what it is.
So here's a sort of murky looking thing in
the center here, you can ignore the bright
thing in the upper right hand side that's
just an annoying star that got in the way.
What we're looking at is a teenage galaxy.
This is an object, this image was made using
one of the giant Keck telescopes in Hawaii,
it's a seven hour exposure time.
If you think when you take your digital camera,
right, that's a tiny fraction of a second
to get full exposure, it's seven hours worth
of exposure time.
What we're looking at is the ultraviolet light
coming from a baby galaxy or teenage galaxy
that light has been traveling towards for
12 billion years.
So it's way, way back pretty much at the dawn
of formation of evolution of galaxies.
Our question was, "Okay, that's fabulous but
is there a supermassive black hole there 12
billion years ago?
Was it there, was it doing anything?
Could it have played a role in the late evolution
of this system? Cause this system will end
up looking like the things we see today.
So, what we did was we used an x-ray telescope,
in fact we used NASA's great observatory called
Chandra which is an orbiting x-ray telescope
to do x-ray astronomy from space cause the
atmosphere blocks most x-rays, so we looked
for high energy phenomena, we looked for signs
of these sort of subatomic particle acceleration
black holes are so good at and we saw this.
We saw a great mess of stuff.
This image, actually I should confess, this
image contains 150 photons of light.
So it's not a particularly impressive image
but it took 40 hours to get those 150 photons
and each one of those 150 photons took 12
billion years to get to us.
What it shows is a super matter black hole
doing exactly what it does in today's universe.
it's spewing out these jets, these streams
of energetic particles which is why this blue
thing is sort of elongated.
Now there are many technical aspects of this
but it turns out that because the universe
itself was smaller 12 billion years ago, more
compact, the universe is expanding, right,
if you go back in time it was smaller.
It turns out that shrunken scale of the universe
means that the way in which the energy pouring
out from around the black hole is converted
into other things was different than it is
today.
In fact, we think that difference means the
black hole had even greater power over what
was going on in these teenage galaxies and
probably stunted their growth.
Without this sort of phenomena, these galaxies
would grow to be vast enormous things, the
likes of which we don't see in the real universe,
so black holes turn out to be a critical component
kind of keeping things in line.
They're like the ultimate gate keeper; you
can't make more stars, I'm sorry.
It's finished and that's the role they play.
So let me, I'm almost done with this piece
of the talk, I know questions would be fun.
What we have learned, I've shown you a little
bit of some of the evidence and many other
aspects of this and many other extremely interesting
pieces of research.
We now understand that super massive black
holes, now why they exist in the center of
every galaxy I've skirted over cause we don't
entirely know the origin.
We suspect that maybe the merger of black
holes, you take two small black holes you
make a bigger black hole and that keeps going
on, we're not totally sure about how they
grow but what we do know is that they are
intimately linked to properties of pretty
much all the galaxies we see around us.
So, for example, these sorts of galaxies in
today's universe we find this remarkable relationship.
If you measure the mass of the stars in the
middle of these galaxies which you could do
with various telescopic techniques and then
make an estimate of the mass of the black
hole in the middle, you find the black hole
is always about one thousandth the mass of
the stars, Now, no matter which galaxy it
is, it is a universal rule.
I wish I knew why it was that [chuckles],
none of us do but it points towards a very
intimate relationship.
But then there are places that don't follow
this relationship.
Galaxies like these, and our galaxy is one
of these, you don't see this relationship
so it's very interesting.
We're not sure what that means, yet.
I have a few more questions, I have a few
more slides after that I can show you.
Let me just finish up this piece.
So to kind of wrap this up into a bigger vision,
where does it lead us, what does this mean?
Well, let's just think about the observable
universe for a moment.
The observable universe by which I mean the
universe that we can see because light has
had time to get to us from its, from objects,
right, so it's about 13.8 billion years back
in time that we can see.
The observable universe contains more than
a hundred billion galaxies.
This is actually a rendering based on a real
survey of galaxies.
So the positions and sort of general size
and shape of the galaxies is accurate.
This is the universe around us, about 400,000
galaxies around us.
The observable universe contains over 100
billion galaxies, maybe it's 300 billion,
maybe it's 400 billion but it's probably not
many more than that.
So it's a finite number.
These galaxies contain a finite number of
stars, maybe about 10 to the 22 stars, over
10 sextillion.
I tried to work this out in Google numbers
but it didn't match up the entire time.
It's a finite number, it's an enormous number
and it's a number, just a nice quote Carl
Sagan once said, "There are more stars in
the universe than all the grains of sand in
all the beaches on planet earth."
He's absolutely right.
That's a finite number of grains which is
interesting.
Why is it this number?
It's particularly interesting to me at least
because stars and the galaxies in them, but
the stars in particular, the stars are the
places that produce all the elements heavier
than hydrogen and helium.
This is an old almost cliché thing to say,
the atoms of the carbon and oxygen and nitrogen
in our bodies were once millions of miles
down in the center of stars that are now long
gone.
That's just how it was.
It's true.
Stars produce all the heavy elements.
They produce things like planets, they produce
the chemistry of the universe and eventually
things like life, at least here on earth.
So there is a connection between the actual
number of stars that the universe has produced,
has ever produced over its existence and the
richness of elements and the possibilities
for chemistry and for the environments of
life.
So I'll stop with this slide, I have a few
more things I could say if anyone wants to
see it they can ask questions about that,
it'll take 5 more minutes and a couple more
slides, if not we can just go to other questions.
But I think one of the most fascinating things
for me, and this is a particular topic in
the book, it's very speculative but it's very
interesting because these numbers of stars,
numbers of galaxies, are clearly intimately
tied to the evolution of galaxies and super
massive black holes.
Who would've thought, I know John Mitchell
didn't think this in the 1700s and I'm pretty
sure when Schwarzschild and Einstein were
fighting it out over whether black holes could
actually exist or not, anyone could conceive
that any such fantastical and bizarre objects
could have any real relevance to the nature
of the universe around us.
But it seems that they do on some level and
our own environment, our own cosmic environment
is a product of all this.
So it's a very interesting question, "What
is our link to black holes?"
So I can stop there, I have a few more slides
available if anyone is interested or we can
just go for general questions.
Thank you.
[Applause]
[Laughs]
>>Caleb Scharf: Questions?
Or shall I tell you the next little bit of
the story?
[Laughter]
>>Caleb Scharf: Oh.
>>male #1: One thing you were talking about
these particles of energy that were actually
streaming out of the black hole and you said
they were moving so fast that the black hole
couldn't trap them, does that mean they're
moving faster than light?
>>Caleb Scharf: No but it's a good question.
So I what I mean is that they are being, that
they're all leaving before they get to the
event horizon.
So all of this is happening close to but not
at the event horizon so anything that does
make it to the event horizon is gone, absolutely,
this is stuff that's going on maybe 2, 3,
4 event horizons out, okay, and because of
that, yes, these particles they can be accelerated
very close to the speed of light but obviously
nothing can travel faster than light and certainly
nothing with mass can be accelerated even
to the speed of light.
It gets very close but not quite exactly.
So, yeah, so again it's the analogy of stuff
going down the drain, you know, you hear the
sound, not from necessarily deep in the drain
but on the edge, on stuff where it's turbulent,
where it's getting mixed up.
But yeah, that's a good question.
>>male #1: So my other question was does the
rotation of the black hole have an impact
on the sort of flat spiral shape of the galaxy?
>>Caleb Scharf: [chuckles] Yeah, so good question.
I, you know, I think the answer is no.
[Laughs]
>>Caleb Scharf: And the reason is that it's
on such a small scale compared to the grand
spiral structure of the galaxy.
So our galaxy is about 100,000 light years
across and the spiral structures you see are
on a similar scale, they stretch for maybe
50,000 light years.
The motion of the central supermassive black
hole is all happening, as I've shown, on a
scale of a few times the radius of our solar
system.
So it's a tiny, tiny scale.
Now, what is interesting is that people have
started to look to see whether, in cases where
we can observe the properties of the matter
swirling around the black hole, right, which
is a kind of giveaway to the orientation of
the black hole, right, if it's spinning.
People started to try to look to see whether
the orientation of the stuff swirling closest
to the black hole is the same as the orientation,
if it's a, if it's the galaxy like ours, a
spiral galaxy that has a definite plane of
motion, if that orientation is the same.
And it looks like it's often close but not
always perfectly aligned and we don't quite
know why.
Maybe sometimes in the formation process of
the super massive black holes they end up
being tilted and it's like a gyroscope, it's
very hard to untilt it.
So, yeah, I mean it's, again, it's a very
good question cause you might readily feel
that there should be some sort of connection.
It doesn't seem to be that there's a direct
physical connection because of the sheer difference
in scale and the scale in which the black
hole is dragging space around with it, that
most extreme effect is also very small, it's
a few event horizons away from the black hole.
Now the earth drags space around with it but
it's at a tiny level, people put up satellites
to measure this but it's a minute effect,
it's much greater around black holes but still
kind of restricted.
Sorry.
>>male #2: Thanks for coming.
I'd read a theory that was speculating that
the event horizons of black holes could potentially
be like a big bang event, possibly creating
kind of a new universe in another dimension
and I was just wondering your thoughts on
that and is there any way that we can eventually
prove or disprove that at this point?
>>Caleb Scharf: Right.
Well, I'll confess that I'm not an expert
on the more esoteric aspects of this.
People have long played around with equations
for objects like black holes and the interesting
thing about, you know, Einstein's description
of the distortion space in time is we have
a mass, whether it's spinning or not, there
are, you can often find different mathematical
solutions for different bits, for different
regimes.
So, for example, you find mathematical solutions
that you extrapolate easily across the event
horizon.
I think it's true some of these solutions
indicate that maybe there's a sort of worm
hole, you go through the event horizon and
rather than end up in the middle of the black
hole there's actually a tunnel through space
or somewhere else or some other time or other
dimension or whatever.
My understanding is that now people feel that
all those solutions are unstable, they're
inherently unstable.
As soon as you put anything there it all collapses.
So there's no way you can, you know, go to
another universe.
All the black hole can itself can be the progenitor
of the universe in some other parallel reality.
So my feeling, my personal feeling is, cause
the other question that comes up is where
does all that matter go?
Inside the black hole, what is it?
We know that, well, as far as we know there
is nothing that can support matter once it
enters inside its own event horizon because
particles would have to be moving faster than
light in order to provide the pressure needed
to stop something from just collapsing into
nothingness.
The thing about, people then say well, there's
a singularity at the center of the black hole,
point infinite density.
That's what the general relativity equations
tell us.
The trouble with the general relativity will
not work on a quantum scale.
It's incomplete.
It's a good description on large scales but
not a very small scale.
At a small scale, space is granulate, at least
this is what we now believe it's because of
the quantum scale things are uncertain.
So one picture that people have come up with
and certainly it comes out of string theory,
is the idea that the center of the black hole
is effectively a very exotic and energetic
type of subatomic particle, that's what it
all comes down to, it's a string that's so
excited that its mass is 10 billion times
the mass of the sun.
What's neat about that idea is that, and again
this is getting a little technical, but this
notion of Hawking Radiation.
So, Steven Hawking purposed that black holes
can actually evaporate and, again, it's because
of quantum things going on close to the event
horizon.
I won't go into it deeper but the short is
the black hole, if given enough time, will
eventually evaporate away.
Just leave, it emits radiation, particles,
whatever.
But then that begs the question what happens
if it evaporates all the way down to nothing?
What are you left with?
Cause everything happens in this event horizon.
String theory kind of gives a sort of elegant
answer to that which is eventually you're
just left with a normal subatomic particle.
Black hole evaporates, evaporates, evaporates,
it gets smaller and smaller and becomes microscopic
and then it becomes some sort of exotic particle,
maybe a Higgs Boson, although it wouldn't
be a Higgs Boson, it would be and then eventually
it would just end up as a boring old electron
and that's it, it's gone.
It just evaporated back to constituent subatomic
bits.
Anyway, sorry, I'm not sure that really answers
your question.
[Laughter]
>>male #3: So my question is that you were
speaking about how at the beginning of the
universe creation that there were these black
holes in the teenage galaxy you showed.
So, I just previously thought that black holes
were formed because so much time passed that
matter kind of collected.
Is it more so that black holes were created
in the big bang and these supermassive black
holes especially or are they created just
with a lot of time passing?
>>Caleb Scharf: Right, it's a great question.
We think that the majority of black holes,
I didn't really get into this cause I put
the emphasis on the supermassive version,
the majority of black holes actually are about
10 times the mass of our sun and there should
be thousands of those in our galaxy.
They're produced all the time by the collapse
of very old stars.
Stars burn through the nuclear fuel, once
they burn through that nuclear fuel they burn
elements, they fuse elements up to about iron
and that point it's a break even prospect
for generating energy and, so, fusion kind
of stops and the core of these stars tends
to collapse and we think, in many cases, can
make a small black hole, small meaning maybe
10 times the mass of our sun and that's been
going on forever.
These giant things in the middle of galaxies,
I think, most people would say, are not related
to anything that might of happened in the
very, very early universe, right, in the exotic
mix of particles and quantum fields in the
very early universe.
These are probably produced because the conditions
in the young universe before you had many
stars, were rather different than today.
As soon as you begin to make heavy elements,
you change the way in which gas can accumulate.
It has to do with, kind of esoteric physics
about cooling.
Heavy elements act like a coolant of gas.
And the cooler gas can get the quicker it
can cool down and the more efficiently you
can make stars and galaxies.
We think in the earlier universe things were
different because you didn't have all these
heavy elements so it might be possible to
get a single cloud of gas under its own gravity
could collapse to make a supermassive black
hole in a pretty short time, relatively short
time, 10s of thousands, 100s of thousands
of years.
So one idea from where these super massive
black holes come from is the part of the kind
of seeding material for galaxies.
They're not a necessary seed for a galaxy
but they're just part of the whole initial
process of making any of the structures we
see in the universe.
So it's, yeah, so it, you know, it's kind
of probably not anything as exotic as some
remnant of, you know, quantum fields in the
early universe and probably more to do with
complex gas physics.
If that answers the question.
Any other questions?
[pause]
>>male #4: Yeah, you kind of mentioned these
plumes that these different black holes will
admit from galaxies.
I was just wondering about our own galaxy,
if we can see any sort of a plume or anything
coming off?
>>Caleb Scharf: Ah, thank-you.
Good question.
[Laughs]
>>Caleb Scharf: Let me show you, so I'll skip
through a couple slides to show you.
So this has been an interesting question,
"What about our own galaxy?"
Now we had thought, until very recently, that
the super massive black hole at the center
of our galaxy was pretty quiet, it wasn't
getting fed much matter, it wasn't doing a
great deal.
And that's been kind of interesting cause
it turns out we think our galaxy, and I'll
just go through this a little fast, our galaxy
belongs to a special category of galaxies,
it's a Green Valley galaxy and that's a galaxy
that's in transition.
We're no longer making as many stars on a
given year as we used to.
We make maybe two or three stars a year, are
formed in our galaxy.
Remember our galaxy has 200 billion stars,
so, you know, it's a small fraction.
It used to do a lot more and there are other
galaxies, redder galaxies that don't do this
at all anymore.
What's interesting is there seems to be a
relationship between a galaxy being a Green
Valley galaxy and what's happening with supermassive
black holes middle.
Most Green Valley galaxies that we see out
in the universe have black holes that are
much more active in their center.
They actually are producing these plumes and
objects and so on.
We hadn't thought that our galaxy was doing
this.
What's interesting is we're now seeing evidence
that it is.
So this, very briefly, this is a map of Gamma
Ray emission coming from our galaxies, this
is really, you're looking at the plane of
our galaxy across the center of this map.
And you can see, though, these two structures,
this was discovered about two years ago, these
two structures, these great regions of Gamma
Ray Emission coming from above and below the
center of our galaxy.
What we think is going on is this, that in
fact our galaxy does have these bubbles around
it but they were produced maybe sometime in
the last 100,000 years, maybe sometime in
the last million years by a supermassive black
hole in the middle.
So it's one of these interesting things of
cosmic coincidence, right, where we happen
to exist in a time when our black hole is
not currently actively eating matter and producing
energy but it did awhile back.
So it may actually be that our galaxy is much
more active, our black hole is doing a lot
more than we had given it credit for.
Let's see, oh, and the interesting thing is
next year, in the next few months, we now
know there is a blob of stuff heading, this
is obviously an animation, blob of stuff,
that red thing, heading for the black hole
center of our galaxy.
Astronomists spotted this a few years ago,
it's on track, depending on what it is it,
may get shredded and we may get a small version
of this black hole eating happening right
in our backyard and that will help inform
us whether or not this is really true that
our black hole, on a cosmic time scales, are
actually an awful lot noisier than we had
given it credit for.
So, yeah, I don't know if that answers your
question but it was a good excuse for me to
show the rest of the slides.
[Laughter]
>>Presenter: Thank you very much.
>>Caleb Scharf: Thank you.
[Applause]
