>> From the Library of
Congress in Washington, DC.
>> Michelle Cadoree
Bradley: Good morning.
I'm Michelle Cadoree Bradley, a
research specialist in the Science,
Technology and Business Division
of the Library of Congress.
This is the tenth season of our
collaboration with NASA Goddard.
And today is the second
lecture in the eight
that we have planned
for this season.
There is a list available
outside the theater
and you can always check our
website to see what's coming up.
The 2014 movie "Interstellar"
has a team of astronauts set
out to explore a system of planets
orbiting a super massive spinning
black hole named Gargantua.
Searching for a world that may
be conducive to hosting uni-life.
With theoretical physicists,
Kip Thorne as a science advisor,
the film has been praised for its
high level of scientific accuracy.
But what is science,
and what is Hollywood?
This presentation will
address the habitability zone
around super mass black holes.
And will discuss the
Hollywood movie,
in light of the physics
governing accretion,
relativity, and astrobiology.
I'm very excited to present
Dr. Jeremy Schnittman,
a research astrophysicist at
NASA's Goddard Space Light Center.
He has a doctorate
in physics from MIT,
and his research interest
include theoretical
and computational modeling of
black hole accretion flows.
Black hole binaries and other things
that I cannot pronounce
at this time.
Please welcome Dr.
Jeremy Schnittman.
[ Applause ]
>> Jeremy Schnittman:
Thank you so much ladies
and gentlemen, it's
great to be here.
It's really fun.
I love talking about black holes.
So really you guys are doing me a
favor to let me come and just go on,
and on, and on about, well it's not
just my hobby it's actually my job
which is a pretty exciting
place to be.
So I will be talking about the
science of "Interstellar" the movie.
You know there's a tendency
especially of physicists
to watch science fiction
movies and try
to pick apart every single
little hole in the plot, or well,
we used to call it at MIT, the well
actually effect because you say,
well actually that wouldn't
really happen that way.
So I'm going to really
try to avoid that approach
because of my great enjoyment of
the movie and my great respect
for Kip Thorne who is the heart,
and mind, and soul behind the movie.
So rather than think of this really
as a critique or a commentary
on the movie, I like to think of
it as kind of like a tribute band
to the Beatles, to you know they
can do things a little bit their own
way, but really the heart and soul
of it is coming from Kip Thorne.
So maybe out in the cart outside,
but I brought my own copy right.
So if anything more you want
to learn about the science
of "Interstellar" that I don't cover
in the talk is really well laid
out in Kip's recent books.
Some of us actually think
that he got Hollywood
to make the movie to
help sell the book.
And you know it's really
a great introduction.
If you like that a somewhat
more technical book,
but still basically a
popular science book
and I would say my all-time
favorite science book is Kip's book
about black holes and time
warp which is "Black holes,
Gravitational Waves, Time Travel."
And the if you're really in
for the heavy duty lifting,
literally right is
what we call the bible.
"Gravitation" by Misner,
Thorne, and Wheeler.
Also is "Magnum Opus."
Got my signed copy.
Okay so in addition to acknowledging
Kips' tremendous contribution
to the field, and this
moving in particular,
I also want to give credit to
my boss, astronaut Piers Sellers
who is both an astronaut, a
scientist and a construction worker.
He built the International
Space Station.
So Piers is an earth
scientist by training.
And he's also been a tremendous
advocate and supporter of a lot
of the work that I do and that
I'll be talking about today
in particular the intersection
of earth science, climate,
exoplanets, and astrophysics.
Which is one of the great
things about NASA Goddard is
that we have all these different
disciplines all working together
and learning from each other.
This is an older picture of Kip.
I just noticed this morning.
See, he's got the Tesla
medallion there, upside down,
but clearly a man ahead of his time.
More recently he's been named one
of the 100 most influential people
by "Time Magazine" is a great
little blurb actually written
by Christopher Nolan.
So he's really become a rock star.
In fact, we just learned
this morning that Kip
and his collaborators, at Ligo the
gravitational wave detector have
been awarded the Breakthrough I
think it's called the Foundation
Prize in physics.
Essentially Nobel scale
$3 million prize
through their discovery
of gravitational waves.
And then here's a picture
from this weekend with Piers
and another Hollywood personality
who came to visit, Leonardo DiCaprio
for those of you like me, came to
visit Goddard this weekend to learn
about some of the research
we're doing there on climate.
So, let's you know we're
going to cover a lot
of different topics today.
Climate, black holes, gravitational
waves, particle physics, exoplanets.
Here's just a good primer on, I
imagine some of you have heard
over the last 20 years
we've discovered
over 2000 plants orbiting stars
outside of our solar system,
extra solar planets, or exoplanets.
And here's a plot of just some of
the properties of those planets.
And it's also a good opportunity
to introduce, just to make sure
that we're somewhat
all on the same page,
the concept of what we
call a log log plot.
Right, you see the x-axis
is units of semi-major axis.
The distance of a planet
from its start in these kind
of archaic units we
call astronomical units.
Not very descriptive,
but an astronomical unit
is a unit of distance.
One astronomical distance is the
distance from the earth to the sun.
So there's one astronomical unit.
So all of the planets on this
side are closer to their stars
than the earth is to the sun.
And then here's the planet's mass
with that scale relative
to the earth.
So there's one earth
mass, 10 earth masses.
And you see that these log log plots
their spacing increases as you go
to the right or as you go up and
it's very useful for physicists
to use these because
we can cover many,
many orders of different
scales on a single plot.
So you know these planets are
10 times heavier than these,
and 10 times heavier
than these etcetera.
Jupiter is up here about 1000
times the size of the earth.
So we have this big clump of planets
up here what we call hot Jupiter's,
very massive planets, orbiting
very close to their host stars.
And then you see a whole
bunch of planets down here,
which are now called this growing
class of planets discovered
by the Kepler Mission
are called sub Neptune's.
So they're basically between
the size of Neptune and earth.
There's no analogue in
our own solar system,
but it turns out these are
some of the most common planets
in the entire galaxy and a lot
of them orbit very close
to their host star.
Now you see there's really
nothing else quite like earth.
Now, that's not really true,
it's just we haven't found
anything else quite like earth yet.
Because these planets
that orbit very close
to their stars are much
easier to see for two reasons.
One, because we use this one
technique that looks for the wobble.
You probably heard of this, right
you look at the wobble of the star
as it's getting pulled
by its planet.
And another technique is you
actually look for little shadow
as the planet passes in front of
the star, decreasing the light
from the start by even
a fraction of a percent.
So both of those techniques
are much easier to use
when the planet is
very close to the star.
So that's why we kind
of have this tendency
to discover a lot more planets
that are close to the stars,
or these ones that are
far away, but very massive
so cause a very big
pull on the star.
So really it's just a question of
time until we push this plot down
and to the right to discover
the true earth like planet.
In fact, another fortuitous
event in the news
that I just saw yesterday was
new planetary system discovered
by a European group with just
a relatively small telescope,
about a two-foot telescope
down in Chili,
they found which now
they claim which is kind
of the new claim every
four months or so.
The most earth-like exoplanet
has yet again been discovered.
A system of three planets, they're
orbiting so close to their start
that it only takes two
days for the planet
to go all the way around the star.
A two-day year.
But even so, the star that they're
going around is so small and so dim,
that it actually could be habitable.
It wouldn't be that
hot on this planet,
even though it's only
in a two-day orbit.
So those are the guys down
here, so about one earth mass,
but much closer to their host
star and yet what I've put in here
with the color scale
is the temperature
of the star right smaller
stars are cooler.
So you can basically
afford to get closer to them
without betting burnt up.
So this, even though they're
not really like earth,
and life on these planets
could be very different,
it could at least be possible.
So this is really the exciting
direction that the study
of exoplanets is going now.
So let's get a little
bit more into details
about that idea of
the habitable zone.
What makes a planet habitable.
So we start off by saying that
we want it to have liquid water
on the surface of the planet.
Now, we know, you know that we're
somewhat limited by our imagination
as how life works on earth.
There's water, it's on the surface,
it seems to be an important
part of life.
It's not simply that we're
limiting our imagination
by requiring liquid
water on the surface.
There are, you know moons of Jupiter
that now we believe have liquid
water under two kilometers
of solid ice and could very
well actually host life.
But if you want to see
that life with a telescope
from 20 light years away it
really helps for it to actually be
on the surface and interacting with
the atmosphere so you know leaking
out methane into the
atmosphere for us to detect
without telescopes
and spectrometers.
So for those purposes we're going
to use as working definition
of what we call the
habitable zone is any planet
that has enough energy
coming from its host star
so that the surface
temperature of the planet will be
between freezing and boiling.
And also since we want it on a
surface, we're going to throw
out planets like Neptune and
Jupiter, which are just giant balls
of gas, because they don't
really have a surface.
So if you want you know little
creepy crawly things to crawl
out of the ocean onto the
shore, you better have an ocean
and you better have a shore.
So we're going to focus for the rest
of the talk really on rocky planets,
kind of earth, Mars,
Venus type of planets.
And we want to see which of these
planets are in this habitable zone,
sometimes called the
Goldilocks zone.
Not too hot so that all the water
would literally boil off the planet
and escape into space.
And not too cold where
everything would just freeze over.
So here's another one
of those log log plots
where again we're plotting
the distance
from the star on the bottom.
But instead of the planet's
mass, now we're plotting the mass
of the star that the
planet is going around.
So here's one, you know
relative to the sun.
So this is the sun and then these
little dots are the solar system
planets right?
Mercury, Venus, Earth,
Mars, Jupiter, Saturn.
And this yellow band is what
we call the habitable zone
and you know fortunately,
earth is indeed
in the habitable zone
so we can live here.
You notice that Venus is a
little bit inside a little closer
to the sun than the habitable zone,
and Mars is a little bit
outside of the habitable zone.
And that is you know
should be familiar right?
We know that Venus is really too hot
to support life and at least today,
Mars seems to be too cold to
support life, although we also know
that in an earlier time it
may have supported life either
through a thicker atmosphere
or a different composition
of the atmosphere.
So, that's kind of not included
entirely in this, you know it's kind
of an extra dimension to this plot,
but it does go into the calculation
of kind of again the typical
habitable zone for a planet
like earth, you have
to include all those,
the atmosphere is actually very
important it's not just what the
star is doing, but it's what
the atmosphere is doing right?
What we all know very well that the
greenhouse effect makes planets,
for example, like Mars much warmer
than they might have otherwise been.
Because the radiation coming
from the star gets absorbed
by the atmosphere and kind
of trapped and it warms
up the planet a little bit hotter
than it otherwise would have been.
One more thing, we mentioned the
mass of the stars on the left here
and you see that as
you go to smaller stars
like I mentioned earlier, the
stars get fainter and cooler.
So you're getting less
radiation from that star,
and therefore the habitable zone
moves closer and closer to the star
because in order to get enough
energy from the star you just have
to move that plant
closer and closer.
Now this dotted line here is kind
of another interesting feature
which is what we call
the tidal locking radius.
And again, you're probably familiar
with this even if you don't know it.
Anyone who has ever look at the
moon and noticed the same side
of the moon always
faces the earth, right.
And the reason is because the
force of the tide between the earth
and the moon has slowed down the
rotating of the moon to the point
where it's locked, it rotates at the
same time that it orbits the earth.
And we know that any planets that
are close enough to their stars,
anything inside this dotted line is
going to have the exact same effect
at the same side of the
planet always facing the star.
So people say that it means that
a day is the same as a year,
but that's actually not quite right
because there's no
such thing as a day.
If you're always facing
the sun, you may have year,
but you don't have a day, it's
kind of odd to think about but.
So when you get to
those kind of planets,
actually there's another
important effect right?
That if you're always
facing the same side
of the planet is always facing
the star, well that side is going
to get a lot hotter, the other side
is going to get a whole lot colder.
So again we have a situation
where the atmosphere plays a very,
very important role in the
habitability of the planet.
You need to use the
atmosphere essentially
to move that heat around.
And fortunately, you now
on earth it gets cooler,
but the entire planet doesn't freeze
at night because we store up some
of that warmth in the atmosphere
so those 12 hours of darkness,
the atmosphere is cooling down, but
not enough to actually freeze us up.
So, we think the same happens with
these planets down here that are
so close to their star, like
the ones that we just discovered
with those two-day years,
they're always going
to be facing the same side
of the planet to the star.
This has an important effect on
the climate too because the clouds.
Now imagine some of you have
flown in an airplane before.
You look out the window,
you look down and if any
of you have every flown over the
ocean, sometimes you look down
and you see the ocean, sometimes you
look down and you see the clouds.
The clouds are white.
The ocean is blue, or dark blue.
Right? Well it turns out that
actually makes a really big
difference on the weather
and the climate
of the planet is whether you have
clouds, whether you have ocean,
or whether you have desert,
or whether you have forest.
All of those actually look
very different to the star,
so that light coming
from the star is going
to either just reflect off
the planet if it hits a cloud,
because clouds are white and
they're really good at reflecting.
Or if it hits the ocean it will
be absorbed and turned into heat.
To this group out of the University
of Chicago recently wrote this paper
that showed that you
go from a what we think
like an earth-like
planet a simplified model
but an earth-like planet
nonetheless.
This is kind of a map of the globe
where the color is the
fraction of clouds.
Okay. Sorry.
Just giving me a reminder
to give this talk.
So you see at the tropics
around the equator there's a lot
of clouds right?
This is where you get
the rainforest.
There's a lot of rain,
there's a lot of clouds.
And then at you know
plus or minus 20,
30 degrees latitude you have these
very dry, desert like regions.
And the reason is because of these
circulation models in the planet
as the moisture rises up at
the equator from getting heated
from the sun and it rises, cools,
turns into clouds and rains.
And you have these
large circulations
where it's the circulation
model where the air goes up,
moves up to the different
latitudes and then comes
down in what we call Hadley
cells of atmospheric circulation.
And those since they're coming from
way up high where there's not a lot
of moisture, they come
down over the desert,
there's no moisture to rain out.
So that's why the deserts are
dry and the tropics are wet.
Now because the earth is rotating
relatively fast, once a day,
these clouds and whether
patterns is going to get just spun
around the earth and
it all averaged out.
Going from here over to hear,
basically just take the planet
and stop it, due to
that tidal locking,
where you're always facing the same
side of the planet facing the sun.
You see a completely
different effect.
You have one giant cloud facing the
star because you have this one part
of the planet that's getting heated.
The water comes up out of the
oceans, goes to the higher altitude,
cools off, forms giant
clouds and rains back down.
You're essentially putting
up a parasol blocking the
planet from any more sunlight.
And that allows us to go from here,
this amount of energy you're getting
from the sun, which from earth
is 1365 watts per meter squared.
You can more than double the amount
of energy that you're pumping
into the planet and you just
build up a bigger cloud,
a bigger sun umbrella
and it actually still
remains habitable whereas
if it were rotating, you
wouldn't get that effect
and you wouldn't be able to
protect yourself from the sun.
So that was basically a
longwinded way of saying
that when you're tidally locked
to your host star, you can afford
to get a lot closer to it
and not boil off your oceans
and still be habitable.
For basically the rest of the
talk, we're going to condense all
of that information into two
numbers, which is just the amount
of flux hitting on average you
know some part of the planet,
has to be between these two numbers
120 and 750 watts per meter squared.
You don't have to remember those,
just remember that since most
of the stuff we're going to be
talking about with black holes,
we're going to be talking about
energy coming from the black hole
or from these environments
onto the planet.
And we're going to assume that
somehow the planet finds a way
of converting that energy into your
kind of nice room temperature heat
and it's going to be able
to do so within this range.
So that's what we're going to
use as our working definition
of the habitable zone for
the rest of this talk.
Between 120 and 750 watts.
Okay. Now, we have to figure
out what does this have
to do with black holes.
I imagine some of you have seen the
movie, some of you may have not.
If you came to the talk you had
to kind of assume you were going
to have at least a couple spoilers.
So, here we go.
Okay so again, remember what
I said at the beginning.
We're not going to pick apart every
little plot hole in the movie,
but basic thing is we got a wormhole
out at Saturn, we're going to go
through the wormhole
to another galaxy
and explore these three
planets orbiting
around a black hole
in the other galaxy.
And look for which one is most
promising to support the human race.
Now, some of these may be stretches,
but what I like about this whole
scene and this whole approach is
that it actually very closely
resembles NASA's official policy
for exoplanet exploration.
No, we don't have an
underground secret facility
that I can tell you about,
but it's essentially this idea
of triage right.
So when you want to explore
a large number of systems
with a limited number of resources
you do this multiple cuts right.
So for example right
now we're developing
at Goddard this mission
called TESTS,
the Transiting Exoplanets
System Explorer.
I don't know what the other S
is, second s is for savings.
And it is because the mission
TESTS is a small, very quick,
relatively cheap mission it's
going to go up and just look
for these little shadows of planets
moving in front of the stars.
At say the closest
100,000 stars to the earth.
And it's just going to look at
each one you know for 15 minutes
and come back and look at
it for 15 minutes again.
And in doing so it will
identify specific targets
that then we're going to use the
next really big mission from NASA,
the James Webb Space
Telescope is then going
to then focus its huge
mirror and spectrograph
at those planets to
get much better data.
Now it can take hundreds and
hundreds of hours of staring
at a single star to get enough data
to even measure a single absorption
feature in the atmosphere.
So that's why you have to
use something like TESTS
to find the good candidates
for something
like the James Webb Space Telescope.
It's really a very reasonable
way to allocate your resources.
And then ultimately as
they show in the movie,
right there's really no substitute
for in situ measurements.
To actually go to the planet,
get down there take
atmospheric measurements.
Take soil samples, which we are
doing in our own solar system,
if not yet other solar systems.
So that's the basic idea is they
have to explore the properties
of these three planets orbiting
around a supermassive black hole.
Now, I'm going to go
through you know the rest
of the talk we're going to kind
of explore maybe some additional
information they could have used
in narrowing down their choices
of which are the most promising
of those three planets.
But at the end of the day,
again we really are limited
by our own imagination right now.
So we're thinking of well what
would an earth-like planet look
like if you suddenly put it
into orbit around a black hole.
Now, in reality anything orbiting
around a black hole probably is
nothing like an earth-like planet.
Instead of water, you know they
might have liquid lead oceans and
yet still be perfectly comfortable
for whatever creatures they have
there, but at least from the point
of view of trying to look
for an earth type planet
around a super massive black
hole, we'll use what we know
about earth climate and the type
of habitability defined
by the liquid water.
So, remember this plot,
with that little dotted line
about tidally locked planets.
So now I scaled up the mass
instead of the star, now it's going
to be the mass of the black hole
that this planet is orbiting.
So you see these are now,
again anyone who's not
entirely comfortable
with scientific notation 10 to the
8th that's how you read that number,
10 to the 8, or simply
1 followed by 8 zeroes.
So a hundred million
times the size of the sun,
that's kind of the prototypical size
of what we call a super massive
black hole and as Kip outlines
in his book, that's really
the target mass he had in mind
for Gargantua, the
black hole in the movie.
So that's really the
number we're thinking about,
which means that any planet
within about 200 astronomical
units would all be tidally locked.
The gravity is so strong, it would
essentially block the entire solar
system as we know it, would be
locked into that rotational fixing
so that it's always going
to face the same side.
The same side is going
to face the black hole.
So I think we're pretty safe
in using that assumption
of that potential huge cloud
deck to help protect us
from excessive radiation.
So it's a good time to introduce,
I think this may be the only
equation in the entire talk.
Which is something called a
gravitational radius, right.
It's also a unit of light
and conveniently enough
for 100 million solar
mass black hole,
one gravitational radius is exactly
the same as one astronomical unit.
So you don't even really have to
think of any new units or equations.
So this is simply the Newton's
gravitational constant times the
mass of the black hole divided
by the speed of light squared.
Another convenient
feature of this equation is
that for most black holes, this
is the size of the black hole
in that this is the radius
of the event horizon.
So down here at one gravitational
radius is the event horizon.
Out here at 100 gravitational radii,
that's essentially 100 times
further away from the black hole.
So these are the units that
we're going to use for the rest
of the talk, all scaled in
as a fraction of the size
of the black hole, as a
fraction of the event horizon.
And again, pretty much everything
we're going to be looking
at is going to be inside of
that tidal locking radius.
So we got the mass, we
got the tidally locked,
now we have to figure out
how to replace this axis
with what we had before
for the stars was how much
energy are you actually getting
out of the black hole, right?
Black holes are black.
Well, not exactly.
Right? Black holes are actually
really, really, really bright.
And the reason is because most
black holes that we can see
that we can measure, of course a
strong selection of them is the ones
that are bright, the ones that
have gas orbiting around them
in something called
an accretion disc.
So here's a little artist impression
of gas going around the black hole.
You see that basically it
looks like a planetary system.
Everything's going around nice
flat plain on nice circular orbits.
And you can kind of see from,
again the artist impression
that the accretion disk
gets brighter and brighter
as it gets closer to the black hole.
The gas as it gets pulled into
the black hole gets heated up,
hotter and hotter.
So it becomes brighter
and brighter just
like hotter stars are
brighter than cooler stars.
So this is the artist impression
here is the astrophysicist
impression, and the more or less
the same picture that they moved
in the movie promotion, this is
the one that I made on my computer.
Here's the turbulent gas
moving around on these orbits
in the accretion disk
around the black hole.
We're looking at the
accretion disk almost edge on.
So it should look like a
flatten pancake but because
of the super strong gravity
of the black hole the
light actually gets warped
by what we call gravitational
lensing.
So this huge arc in the back
is actually we zoom in here,
it's actually photon's light from
the far side of the black hole.
It gets bent by the
black hole's gravity
up into this arc above and below.
You also see the light
coming, gets bent from below.
This inner circle here
is even cooler.
Because this is light that goes
around the black hole
the entire time,
and then hits the accretion disk and
then escapes out to the observer.
So you see these characteristic
light rings around the black hole
and that's due to the
extreme gravitational warping
of space time around the black hole.
Here is a plot of again, another
one of these log log plots.
Now, we're plotting
the distance from,
this is essentially the
distance from the horizon.
The distance from the
edge of the black hole.
So we can get very, very close
to the black hole a hundredth
of a gravitational radius
away from the horizon.
And on the Y-axis this is a
temperature of an accretion disk.
So you see that the accretion
disk as it goes closer and closer
to the black hole, it
gets hotter and hotter.
But then it turns over
and goes down to zero.
All these different
curves have to do
with different black
hole spins right.
Just like planets spin, stars spin,
we believe that black holes spin.
But when a black hole spins, when
it rotates, it drags the fabric
of space time along with it.
Pulling everything
along in its wake.
So this gas can get
closer, and closer,
and closer without falling
into the black hole yet.
This blue curve here is for a
black hole that doesn't spin,
the gas goes in, it
gets to a certain point
and then just plunges
down the drain.
As you go to higher and higher spins
the gas gets closer, and closer,
and closer to the back hole.
It gets hotter, and hotter, closer
and closer to the event horizon.
And we measure this spin basically
is just a number between 0 and 1.
Zero is no spin, one
is the maximum allowed
by Einstein's Theory of Relativity.
So up here is a maximally spinning
black hole and that the Gargantua
in the movie is also considered to
be just about maximally spinning
and you see, so the temperature goes
up, actually almost 200,000 degrees
of the accretion disk as
it gets a heated up just
about to fall into the black hole.
Now our sun is about 5700 degrees.
Let's call it 6000 degrees,
now that's in Kelvin,
or Centigrade just about the same.
So our sun, which is very far away
at 6000 degrees is
enough to keep us warm.
So what do you think it would be
like if you were right
outside the event horizon
with an accretion disk
surrounding you 200,000 degrees.
Well, your planet would
be then 200,000 degrees.
A little bit too hot
to support life.
So what we need to do is essentially
dial that temperature way
down to the few hundreds degrees.
Room temperature let's
say is 300 degrees Kelvin.
So we want to dial this temperature
down from 200,000 degrees
to 300 degrees.
There actually is a very
simple way to do that.
If you just dial down the amount
of gas in the accretion disk.
If you put less gas piling into the
black hole, it essentially cools off
because there's less energy
to turn into radiation.
So we're just going to
dial that accretion rate,
that gas way down until
we get something
that is a little bit more habitable
and looks a little
bit more like the sun.
So there's Miller's Planet is
the one that's orbiting very,
very close to Gargantua.
And you saw from the visuals,
right, let's take a, it's Hollywood,
but if you wanted to really pull the
umm actually approach to this movie,
right you see that it looks
kind of like the sun, right?
It's yellowish, white, you know
we can see it with our eyes.
If it were 200,000 degrees it would
be blasting us with UV radiation,
but it looks more or less like
the sun in all the visuals.
So you know Kip talks about it in
the book and we're going to infer
from that that the temperature of
the accretion disk is comparable
to the temperature of the
sun, say 5 or 6000 degrees.
So, in order to do that
what you need to do is dial
that accretion rate way down
from, let's call it one.
Unit of one is kind of the
maximum accretion rate.
Down to 10 to the 12 times less
accretion rate is what you need
to get the temperature down to
where a planet could be habitable.
So the way that you read this kind
of graph is there's kind of two ways
to do it you could say, well let's
say the accretion rate is 10 billion
times less than maximum, then
where's the habitable zone you have
to go out here and you see
the habitable zone is right
around 10 gravitational radii.
To get down to the
temperature of the sun,
it turns out you need an accretion
rate of 10 to the minus 7 so that's
up here, and the habitable
zone would be out here
at about 100 gravitational radii.
So, we're not critiquing
but we're exploring right?
Miller's Planet is down here,
right outside of the black hole.
It is so far inside of the
habitable zone that the temperature
on the planet would essentially be
thousands and thousands of degrees.
Which if you can see the accretion
disk you would have already
known that.
So the only, you know if the
accretion disk looks like the sun,
way up here, then you only want to
look for planets that are out in
that habitable zone, hundreds
of gravitational radii away.
This is well we can skip
this is just a slight detail.
The problem is the only way
that you could actually dial
that accretion rate down
to these temperatures,
it turns out that the disk would
be so thin, the amount of gas
in the disk would be so little, it
would cease to be a disk altogether.
In fact, that's exactly what we
see of the black hole in the center
of our own galaxy, Sagittarius A
star is a super massive black hole
in the center of the Milky Way
and it looks nothing
at all like Gargantua.
It doesn't have an accretion disk.
It doesn't have this nice
increasing temperature.
It's just has a big blob
of hot gas that we can see
with the Chandra x-ray telescope.
And it's very low density,
but very hot gas.
Just kind of freefalling
onto the black hole.
You don't see these nice thin disks.
So, okay so let's get rid of the
accretion disk picture altogether
and now we'll say but the heat
source is coming from this gas,
just kind of freefalling
onto the black hole.
Now the problem is
the planet's going
on a nice circular orbit
around the black hole.
So if you're in an accretion
disk, you're going along
with the accretion disk on
these nice circular orbits
and you know all that
matters is the light
that you're getting
from the accretion disk.
But if you're going on a circular
orbit around the black hole,
and all this gas around you
is just freefalling down,
what's going to happen?
You're actually going
to smash into the gas
because this one's going this
way, you're going that way
and you smash into the gas.
And gas falling into a black
hole as it gets closer and closer
to the black hole goes
faster and faster
until essentially it's
going the speed of light.
So you're going to have this
planet getting sandblasted
by the surrounding gas hitting
it at nearly the speed of light.
But, okay we can do that remember we
said we assume the atmosphere had a
way of recirculating the energy.
All we care about is
what's the total amount
of energy getting absorbed
by the planet.
Well, this is what it looks like.
You just have to dial that accretion
rate way, way, way, way down.
Because again, as you get closer
and closer to the black hole
that gas falling in is going faster
and faster so you just have to dial
down the accretion rate, you get
less and less gas going faster
and faster and that's the that
gives you the amount of gas
that would still allow the
planet to be habitable.
Essentially off the charts.
Okay so let's assume that since
they were able to build a worm hold,
this advanced civilization has found
a way to get rid of all that gas
around the black hole to
kind of solve it entirely
from destroying the planet.
Well, there's yet another
problem we have to worry about.
Okay so this is essentially,
I would say the most important
point of the entire talk.
Because it's the one thing
that I came up with that's not
in the Kip Thorne book, right,
it's this plot right here.
Right? As you get closer and closer
to the black hole time slows down,
right we all know that Einstein says
that gravity can warp
space and time.
So as you get closer and
closer to the black hole,
like Rombley just said, you
know relativity tells us
that time slows down.
So he also says that one hour
is equal to seven years, right.
That's one hour is equal to
60,000 hours in seven years.
So you have this time
dilation effect of a factor
of 60,000 right that's
way over here.
So to get that effect you
are essentially forced
to put Miller's Planet so
close to the event horizon,
you know 0.00004 gravitational
radii away from the event horizon
that in order to get that
extreme time dilation effect.
So, okay let's you know,
let's work with this.
What then happens when you
want to say talk on the radio,
right you're going on
your little landing ship
down onto the planet you left
the mothership behind far away.
You're talking back
and forth on the radio.
Or let's say you're doing Morris
Code with a laser pointer, right.
So I'm let's say I'm on the
planet right and I'm talking back
to the ship and I'm sending a little
blip every second, except that blip
from the point of view
of the ship far away
from the planet is only going
to get one blip every
60,000 seconds, right.
Let's turn it around the other way.
Let's say you're on the ship
sending little Morris code
to people on the planet.
You're sending a little
blip every second,
they're getting 60,000
blips a second.
You know right on top
of their heads.
And if it's a laser pointer,
there's a much bigger problem,
right that a laser,
right what is a laser,
it's a perfectly coherent
wave radio wave,
or you know electromagnetic wave
that has exact perfectly
consistent frequency.
The frequency of a laser is
actually just like a clock.
So this laser is actually hitting
the screen just like Morris code,
but hitting it you know
10 the 15 times per second
with a little you know photon wave.
Now you multiply that, also has
to get multiplied by 60,000.
So from the point of view of a
laser that's what we call red shift
or blue shift.
So now instead of a laser
hitting the people on the planet,
you're essentially hitting
them with an x-ray death beam.
Okay? So, and that's all
completely inseparable
from this idea of time dilation.
If you're going to have that
factor of 60,000 times dilation
and Christopher Nolan absolutely
demanded it for the plot right.
He told Kip, he said,
nope that's nonnegotiable.
Then you're going to have
also all the radiation hitting
that planet is going to be
60,000 times more energetic
than it was admitted by.
Okay let's work with this,
just don't shine a laser
pointer on the guys, okay?
Right. Problem solved.
No. Well turns out the entire
universe is a giant laser pointer,
right?
Has anybody ever seen this picture?
This is the cosmic
Microwave background, very,
very low frequency radio waves
that permeate the entire universe.
Right? And it's got these little
fluctuations because some spots
in the sky are a little
warmer than others,
but you basically have an entire
sky of radio waves at very,
very low temperature, two
degrees above absolute zero.
Well let's see what this would
look like to the point of view
of a planet or a spaceship
orbiting a black hole.
As you get closer to the black hole,
okay so there's the black hole,
there's the gravitational lensing.
But now you're seeing like asymmetry
between the front and the back.
And this is a, I have
to kind of step away
from the mic here this is
[inaudible] all skied out.
So picture yourself on the space
station, on a spaceship like this
where the black hole is
on your left and in front
of you is this area here, and to
your right, projected this area,
this area here is behind you,
right that's how this kind
of, this projection works.
As you get closer and closer to the
black hole, you're moving faster
and faster orbiting around it.
The black hole shadow
gets bigger right.
Now we're at 5 gravitational radii.
And this patch of radiation in front
of you is getting hotter and hotter.
Now it's up to a whopping 4
degrees above absolute zero.
Get even closer the black
hole essentially takes up half
of the sky, right, the black hole is
that entire area to the left of you
and right in front of you is all
of the entire cosmic radiation
of the universe squeezed into
a single point and hitting you
at a blue shifted frequency.
Now frequency and temperature
are actually the same thing.
So as we go zooming closer,
and closer, and closer,
now we're up to 15 degrees.
But if you get to the point
where your time dilation,
your blue shift is
a factor of 60,000,
you get the background radiation
temperature goes from 2 degrees
to 120,000 degrees, beaming
at you right in the face
with this huge ultraviolet flux.
Again, not so good for habitability.
So here's the plot you know
as you get closer and closer
to the black hole, here's just
the total flux that you're getting
from the CMB coming at you
and here's the little
band of habitability.
So Miller's Planet is way up
here, about 100 times more flux
than you could possibly
survive and that's just
from the cosmic microwave
background.
But, okay so you back it away a
little bit and you're good to go.
Well, not quite right.
There's a picture of the
center of our galaxy,
well it turns out that also in the
center galaxy in addition to all
that gas, there are a lot of stars.
In fact, if you were to live
in the center of the Milky Way,
the night sky would be
100,000 times brighter.
You could read at night from
starlight, just because there's
so many more stars packed
into a small region.
So now instead of just worrying
about the cosmic microwave
background you have all these stars
just everywhere surrounding you,
all getting blue shifted
and raining down on you.
So that gives you the flux from the
starlight is actually much higher.
So you have to push your
planet even further away
from the black hole
to still survive.
Okay we got very advanced
civilization,
we'll just build a giant Dyson
sphere around the planet,
which is another famous
idea in science fiction
where you essentially build a
giant metal sphere around a star
or a planet that can either absorb
light or reflect all of the light.
Okay so all of that cosmic radiation
coming inform outside getting blue
shifted from the black hole, we'll
just build like a giant mirror,
disco ball and just reflect it out
and out planet will nestle
inside nice, safe, and sound.
Neutrinos.
Could go through anything.
They can, you know 10 billion
just went through my thumb nail.
They're everywhere.
Now, fortunately for us neutrinos
basically could just care less
about us, they just
zip right through us.
But if you get enough of them
they start to deposit energy.
And just like there's the
cosmic microwave background,
there's also a cosmic
neutrino background.
The universe is just
filled with neutrinos.
But because they more or
less go right through you,
you have to get really close, let's
say 10 to the minus 11 radii away
from the horizon to get
enough neutrino flux lighting
up the atmosphere, in order
to get that habitability zone.
But, let's say the neutrinos don't
just get absorbed in the atmosphere,
the neutrinos could also get
absorbed in the core of the earth,
the core of the planet and
then heated up radiation
and then essentially you have
geothermal heating of the planet
from neutrinos, yes NASA
does actually pay me to think
about these things, right?
And that moves it way out because
you get a lot more cross section,
a lot more opportunities to
get heated by the neutrinos.
And then we can actually
push it out even further
because these are the
C neutrino background,
the cosmic neutrino background.
And it turns out actually
most of the neutrinos going
through me right now are not
coming from the distant universe,
but they're coming from the sun.
right the sun generating
neutrinos in its core
and its core nuclear
reactor all the time.
So when you use those neutrinos
instead it actually goes much,
there's a lot more flux, you have
to push it way out and then you have
to push it out even further because
remember now we're in the center
of the galaxy where there are
tons of stars, tons of neutrinos
and you're pushed out so far, you're
basically out to the same radius
that you were for the cosmic
microwave background radiation.
So even with your Dyson sphere, the
neutrinos are still going to heat
up your planet above
any habitability zone.
Let's say again, we've got super
advanced civilization we can build a
Dyson sphere we can even
build a neutrino Dyson sphere.
Just you know a kilometer of
lead around the entire planet
to protect it from neutrinos.
There's dark matter.
I just like this movie.
It's a movie I made a simulation
of dark matter particles
orbiting around a black hole.
And there's just dark matter
everywhere in the universe
and we don't know anything about it
except that it reacts to gravity.
And we know that black holes have
a whole heck of a lot of gravity.
So we know that dark matter
is going to all get pulled
in toward black holes and when
it's a spinning black hold
like Gargantua, it actually
wraps the dark matter around it
and it almost looks like a ball of
yarn as these particles get pulled
around the black hole from the
twisting and warping of space time.
And that, you put a planet
down in the middle of that
and you're just going to get
completely bombarded by dark matter.
Now, since we don't
actually know anything
about dark matter I
couldn't make a plot
because I don't know actually how
dark matter will affect the planet,
but I imagine it's going to be bad.
This is our last source of death
on a planet around a black hole.
Gravitational waves, right?
Today, like we said celebrated with
$3 million, Kip Thorne's discovery
of gravitational waves with Ligo.
I don't know if any of
you have seen this movie,
this is from the press conference
at NSF earlier this year.
Those are two different filters
on the gravitational wave.
That was it.
That little zip.
That was three times the size of
the sun, e=mc squared being turned
into pure energy in
about 20 milliseconds.
All right?
You're going to have
the exact same effects.
And all of these other
time dilation blue shifts.
You have a universe filled
with gravitational waves,
and they're all going to
be hitting your planet
and there's nothing
you can do about it.
When you get closer and
closer to the black hole,
those gravitational waves are just
going to get amplified to higher
and higher amplitude, higher
and higher frequency
and bombard your planet.
Unfortunately, this is why it
took 100 years to detect them,
even worse than neutrinos really,
they really just fly
through everything.
So you're going to have to get
almost so, well really so close
to that black hole that basically
all other bets are off in order
for the gravitational waves to
have any real effect on you.
So we're going to leave
gravitational waves,
and I see the Einstein's Outrageous
Legacy, that's the sub title
of this book that we
mentioned before right?
"Black Holes and Time Warps,"
Einstein's Outrageous Legacy.
Einstein predicted both black
holes and gravitational waves.
And we're going to leave it
by saying those gravitational
waves might be the only thing
that won't kill you around a
black hole, which I think is kind
of a nice poetic, you
know consistency
within Einstein's theory.
Here are all the things
that will kill you right?
We talked about the accretion
disk, the sand blasted
by an accretion cloud, the cosmic
microwave background, the starlight,
the neutrinos, dark
matter, and maybe
or maybe not surrounding
gravitational waves.
But we want to end on
a more positive note,
so instead of thinking these things
can kill you all right these are
nine ways that a black hole can
keep you warm at night and look
for a nice comfy place to
relocate the human race
after we've destroyed earth.
To through the wormhole
to Gargantuan and settle
down in a nice planet,
comfortably in the habitable zone
around a super massive black hole.
Thank you very much.
[ Applause ]
>> Michelle Cadoree Bradley: Oh,
that was so absolutely wonderful.
I do know that tonight
I'll be going home
and treating our earth
just a little bit better
because I don't think we'll be going
and finding any other place
to go to any time soon.
So we'd like to again thank Dr.
Schnittman for coming with us today.
Let's just give.
[ Applause ]
And we can begin our
question and answer period.
And we'll ask you to
repeat their questions
for the purpose of our webcast.
>> Jeremy Schnittman: And actually
I've put up the last slide for those
who haven't seen the movie,
or more importantly the people
who have seen the movie, but maybe
were confused about a thing or two,
this should clarify everything.
Yeah.
>> So you're assuming in the
talk where orbiting something
around a black hole is
circular or elliptical
but it doesn't move forward, but we
know that the gravitational effect
on the black hole is
going to pull that planet,
exoplanet whatever
eventually toward it.
What's that timeframe like?
>> Jeremy Schnittman: Right, so the
question was what's the timescale
like for the planet to actually
get pulled into the black hole
as it spirals in through its orbit.
So it's actually pretty
similar to that of planets
in our solar system, right?
We go around the sun on
circular or elliptical orbits
and we're constantly getting
pulled in toward the sun,
but we actually don't get really
any closer to the sun and that's
because we have angular
momentum right.
And sometime you may learn about it
in physics classes,
centrifugal force.
You kind of want to go out, the
sun's pulling you in and you end
up on this nice stable orbit.
The one difference with the black
hole is you also have gravitational
waves, which is essentially
a drag force on the planet.
But unless you yourself
are also a black hole,
that little planet is basically,
think of it as leaving
a wake, right.
So a big boat leaves this huge wage
and there's a lot of drag on a boat.
But you know a water
bug basically just skims
across the surface of the water.
So these little planets
that are much, much, much,
much smaller than the black hole
are just like water bugs skimming
around the surface of space time
without really any losses of all.
The bigger problem, again is
due to that time dilation right.
Factor of 60,000.
That planet, even if that planet
was kind of created at the beginning
of the universe and put next
to that black hole by hand,
essentially you take the
entire age of the universe,
say 13 billion years,
divided by 60,000
and the planet could really only
be 200,000 years old from its point
of view, right, the clock on the
planet is only 200,000 years old.
So that's actually another way that
it would probably be inhabitable
because it takes a while
for a planet to really set
into a nice equilibrium
before you want to live
on it otherwise it would just
be covered with molt and rock.
Anyone else?
Yeah?
[ Inaudible Audience Question ]
Well, the question is why isn't
everything just pulled straight
into a black hole.
And the answer is angular
momentum right?
The famous example of angular
momentum is the ice skater, right?
They're spinning around
with their arms out,
they pull the arms in
and they go faster.
But if you've ever tried that
trick, you actually feel that pull,
it wants to pull your
arms back out again.
So the same with the planet, as it
gets closer, it's spinning around
but it has that centrifugal
force making it feel
like it's trying to
pull back out again.
And it's the gravity that's
pulling it in and it just balances.
And except when you're very,
very close to the black hole they're
basically like Newtonian gravity.
So it's going to look just
like the planet's going
around the sun in the solar system.
We did talk about for the
non-spinning black hole is there
anything that's not spinning
at the maximum level.
You do get to a certain
point and it's very,
very close to the black hole.
You get to a certain point
where you do just fall in.
And that's very much a
relativity predication.
Newtonian, you just get closer, and
closer, as close as you want to get
to an infinitely small point.
But in general relativity,
there's this special point beyond
which you just are going to
always just plunge right in,
but it's very close
to the black hole.
Yeah?
[ Inaudible Audience Question ]
Right. So the question is what's
the scaling, the relation of energy
to distance from the black hole.
So if you're far enough away that
it just looks like a bright spot
in the sky, then it's going to
again, behave just like the sun.
the flux of energy goes like
one over the distance squared.
But in some of the ideas
that we were showing here
where you're actually in the
accretion disk or you're surrounded
by this hot matter, then it's
going to be more complicated.
You know you're essentially
depends on how that temperature
in the accretion disk changes
as a function of distance.
So accretion disk, the temperature
typically goes up like one
over the distance or something
close to that, but then it turns
over and falls off again.
So it's not a simple relation,
unless you're far enough away
that it all look Newtonian.
[ Inaudible Audience Question ]
I mean I've seen press
releases from Stephen Hawking
which unfortunately is his primary
form of communication these days.
So from a scientific point
of view, it's sometimes hard
to evaluate the details
of a press release.
From what I understand though,
I mean his whole career has
really focused on the effects
of quantum mechanics very close
to the horizon of a black hole.
Information theory, where does
quantum uncertainty go how does it
behave on the horizon.
And I've actually, every
single effect that I've talked
about today is purely classical,
non-quantum effects involved here.
And that's basically, my research
is very much a classical research.
So even if Stephen Hawking did write
a paper I'm probably not the one
to evaluate it.
Yeah?
[ Inaudible Audience Question ]
Right. So we do measure
the total mass
in dark matter throughout
the universe.
That's how we know it exists right?
We see how it effects,
because it effects gravity.
So all we have to do is look
it orbits around massive things
like galaxies and clusters
of galaxies
and you can actually see the things.
Everything is moving
faster than it should.
So you can essentially
work backwards
and say oh there must be
more stuff there and that's
where the whole idea of
dark matter came from.
When it comes to looking at
something like the solar system,
or in this case a black hole, when
you get down to those small scales,
the whole gravity is dominated
so much by the black hole,
or by the sun, that it's very,
very hard to measure the
amount of dark matter, right.
In the solar system
is the equivalent
of about 1 proton per cubic
centimeter worth of dark matter,
whereas it something
like 10 billion times
that much of the regular matter.
So it's very hard to measure on
these scales, you have to look
on very large scales,
not small scales.
>> So we know it exists, we
just don't know where it is.
>> Jeremy Schnittman: Well we know
where it is on a very broad area.
You know we know it kind of clumps
around galaxies and clusters,
but you can't say whether it's on
the size of a solar system or not.
>> Michelle Cadoree Bradley:
Well I think we're going
to draw this program to a close and
thank you for attending and we hope
to see you at our next program.
[ Applause ]
>> This has been a
presentation of the library
of Congress visit us at loc.gov.
