(light music)
- I'm Eliot Quataert, a professor here
in the Astronomy and Physics Departments
and current chair of the
Astronomy Department.
So, this is our annual Distinguished
Astronomy Lecture where
we bring an eminent scientist
from another institution,
give a public talk tonight and then Fiona
will be here tomorrow
meeting with many of us
and giving a science talk
later in the afternoon.
So, tonight's speaker is
Fiona Harrison from Caltech.
She's the Benjamin Rosen Professor
of Physics and Astronomy,
and she's also the chair of the Physics,
Math and Astronomy Division at Caltech.
So, the fact that she's called
chair and I'm called chair
might make you think those
are similarly important jobs,
but they're not.
(audience laughing)
Chair at Caltech is really
more equivalent to Dean.
So, Frances Hellman's position.
That's a job that has far
more power and responsibility
and money than I do.
Which frankly, I'm grateful for.
So, Fiona was an
undergraduate at Dartmouth
and then actually did her
PhD work here at UC Berkeley.
She got her PhD in physics here in 1993.
She worked significantly
at the Space Sciences Lab.
So, for those of you who don't know that,
that's a lab up the hill
that really specializes
in building hardware for NASA telescopes
and in actually operating telescopes.
So, it's an operation
center and actually develops
the hardware for a number
of NASA telescopes.
There are very few
universities in the world
that have the capability to
actually train graduate students
in hardware development
for major NASA projects.
Berkeley is one of them,
Caltech with JPL there
is also one of them.
In fact, the work that Fiona
did for her PhD at Berkeley
was in developing detectors,
so the way you actually
detect X-rays and gamma
rays that went into
the telescope that she'll
tell us a lot about today.
And that is a lot harder than it seems.
If you imagine going
to the dentist, right?
You get an X-ray of your skull.
That shows you the difficulty
of actually detecting X-rays.
They pass readily through our body,
but for astronomy, we wanna
actually gather them up,
collect them and use them
to observe the universe,
and that's one of the things
that Fiona specializes in.
So, after completing her PhD at Berkeley,
she was a postdoc at
Caltech before she joined
the faculty there where
she's been ever since.
She's an expert on astronomical
explosions of various kinds,
gamma ray bursts, flashes of gamma rays,
gas spiraling into black holes,
stellar explosions of various kinds.
And as I said, a lot of her
career has been based not only
in doing observational astronomy,
but in actually building the
tools that enable us to launch
satellites into space and
do astronomical observation.
So, I'm actually a
theoretical astrophysicist,
so I don't know anything about telescopes,
and I have to tell you that
of everybody in the field,
the people that I have the
most respect for are the people
who can actually design,
build and function telescopes.
That's an extraordinary skill
and that's really what drives
our field forward is those
advances in instrumentation.
So, Fiona's work on developing X-ray
and gamma ray telescopes
has culminated thus far
in the launch of the
NuSTAR satellite in 2012.
This is what will be a major
theme of her talk tonight.
That telescope has given us an entirely
new view of the sky at X-ray wavelength.
So, that in particular gives
us information about phenomena
that are very hot, very dense,
conditions that are quite
a bit more extreme than we find typically
here on Earth or in the solar system.
So, the theme of the talk will
be things like neutron stars,
black holes, stellar explosions,
exciting phenomena like that.
For both the science that she's done
with X-ray facilities
and for her development
of the hardware for those facilities,
Fiona has received a number
of prizes and recognition.
I'd like to particularly
highlight the Bruno Rossi Prize,
which is the highest honor of
the High Energy Astrophysics
Division of The American
Astronomical Society,
and her election in the
National Academy of Sciences,
which is the preeminent
intellectual institution
for scientists in the United States.
So, in addition to
everything else she's doing,
running the NuSTAR telescope,
doing science with it,
PIing a new telescope to look
at colliding neutron stars,
Fiona is also the co-chair of the
2020 Astronomy Decadal
Survey in Astronomy.
So, every 10 years the astronomy
community gets together
and tries to make priorities
for what the most important
science to do and the
most important telescopes
to build are for the following decade.
And that's an enormous undertaking
that takes almost two years to do.
It requires gathering the herd
of cats that is the thousands
of professional astronomers
in the United States,
and I think it's really a
testament to the esteem that
the entire astronomical
community has for Fiona,
for her vision for the field
and for accomplishments to date,
that she was asked to lead
this years version of that survey.
So, we're really honored to
have her here tonight, so.
(audience applauding)
- Well, thank you for that introduction.
It's great to be back.
I come back here relatively frequently.
I can't help but go over
for coffee on Durant Street.
Anyway, I'm gonna tell you
today about the NuSTAR mission.
This is what I've spent
most of my career on.
First developing the technologies,
getting NASA to agree to
fund it and launch it.
And so, NuSTAR is the very
first orbiting telescope
that can actually focus
high energy X-rays.
So, it views the universe in
a completely different way,
making images that are
hundreds of times deeper,
a hundred times crisper
than any previous instrument
that we've had working in
this part of the spectrum.
NuSTAR is also a small explorer mission.
This is the smallest stand alone
astrophysics platform that NASA has,
and people often ask how small is small?
It was 160 million for
everything including
the launch and science.
And that sounds like a lot of money,
but when you put something
in space, it's actually not.
So, NuSTAR, as Eliot said,
was launched in 2012,
and what I'm gonna tell you today
is a little bit about the mission itself,
and then I'm gonna talk about a couple
of science highlights
from the mission so far;
measurements of the spin of black holes
and the radioactive debris
from exploded stars.
So, NuSTAR, as Eliot said, is
studying some of the hottest,
densest, most energetic
regions in the universe.
So, I wanna start with the big
picture and kind of reflect a
little bit on the time since
I was a graduate student here,
which was 25 years ago when I got my PhD.
And when I think about this,
we really do live in a
golden age of astronomy.
In the last 25 years,
our view of the universe
has completely changed.
When I was in graduate school,
we were arguing about the age
of the universe to a factor of two.
Now, we're arguing about
the second decimal place,
13.77 billion years old.
And the other thing that was
completely unknown when I was
in graduate school was that
the evolution of structures
in the universe is shaped by
something called dark matter.
And if you look at this
picture over here on the left,
it shows you how from the
primordial soup of hydrogen
and helium, galaxies condensed
and formed and evolved,
shaped by the gravity of
something called dark matter
that we have no idea what it is.
And how will the universe end?
Well, its fate is determined
by something called dark energy.
Also, newly discovered since
I was a graduate student.
So, on the right, what this
pie chart shows you is just
a few percent of the universe
that we study in light
and in X-rays in the kind of
telescopes that we've had.
And I wanna point out that
researchers here at Berkeley
and at LBNL played fundamental
roles in both understanding
the age of the universe,
dark matter and dark energy.
So, how did our view, our
understanding of the universe
change so fundamentally
in such a short time?
I mean, it's just less
than a generation, right?
So, it was through technological advances,
combined with the access to
space that has changed things
and changed our ability to view
the sky in fundamental ways.
So, it's our ability to study
the universe in microwaves.
So, this is the same
radiation when you heat
your cup of coffee in the morning
in your microwave oven, same radiation.
That enables for us to
look all the way back
to just 400,000 years after The Big Bang.
By looking at infrared,
that's the same radiation
that we experience as heat,
we're able to study first
light in the universe.
So, when stars and galaxies
were beginning to form,
and then of course in the optical,
the Hubble Space Telescope
has given us an unprecedented
view of galaxies and how they evolved.
So, combined, it's this
ability to study the universe
in so many ways that's new,
so I'll remind you that
Hubble was launched in
1990 and was fixed so that
it really achieved its
sensitivity in 1993.
That's about when I graduated.
This has all happened
in the last 25 years.
So, what do microwaves, infrared
radiation and optical light
all have in common?
Well, it's all the same
fundamental physical phenomenon,
which is something that never ceases
to amaze me when I think about it.
What's different between them,
so is this oscillation of
electric and magnetic waves,
and the thing that's
different between these kinds
of radiation is just the
distance between the peaks.
So, if you think of an analogy
of waves on the ocean, right?
And you think of the distance
between crests of the waves, right?
For infrared radiation,
this distance is about the width
of a human hair and for
radio waves, same phenomenon.
It's the size of a building.
For ultraviolet, it's about,
the size of a molecule,
and for X-rays, which is
what I'm gonna focus most
of the rest of my talk on,
it's about the size of an atom.
And so, I wanna also point
out one other important thing,
which is if you look at
this temperature scale here
on the bottom of the graph, all right?
You can see that the temperature
in degrees Celsius there,
and the shorter the
wavelength of the radiation,
the hotter the material
is that's emitting it.
So, again, when we study
X-rays, we're studying objects
that are very hot, millions of degrees.
And so, when you have telescopes,
if you wanna observe the entire
universe and all the visible
matter in it at all temperatures,
you really need to go from
radio waves all the way
to X-rays and gamma rays.
So, I mentioned that
access to space is a key,
and I want to explain why that is.
So, now, this is a little
confusing because the scale
is inverted from the last
graph that I showed you.
I couldn't find one where
it was the other way around.
So, here, gamma rays is on the left
and radio wave in on the right.
But anyway, so flip your head.
And what this shows you is
the altitude above sea level
and the little black lines
show you how far radiation
of a given wavelength
or type can penetrate.
And you can see really
from the ground we have
this tiny window in the visible, right?
That's why our eyes evolved
to see visible light,
where radiation can reach the ground
and then again in the radio.
But to cover the entire spectrum,
we really need access to space.
All right, so now you know that X-rays
are just another kind of light.
So, they don't have magical
cleansing properties
and the other thing I'll say about them
is this guy can't detect them
with those glasses, okay?
(audience laughing)
You need very sophisticated
types of mirrors and detectors,
and I've spent, as Eliot told you,
significant time trying to help
develop these technologies.
All right, so here's another view
of the electromagnetic
spectrum going from infrared
on the left to gamma rays on the right,
and this highlights the X-ray
part of the spectrum, okay?
And, we've had very powerful
observatories that have viewed
the heavens in the low energy, all right?
Or longer wavelength part
of the X-ray spectrum.
This is NASA's Chandra mission
and ESA's XMM-Newton mission.
NuSTAR is the first telescope,
as I said, that can truly
focus in the higher energy
part of the X-ray spectrum.
And if you look you'll
notice there's two scales.
I don't want you to worry
about the units, okay?
If you actually studied
physics, you know that we can
think of light as having both
a wavelength and an energy.
But don't worry about the units.
We usually in the X-ray
astronomy community,
we use the top units, all right?
But all I want you to remember
is the number 10, okay?
'Cause 10 in units you
don't have to worry about,
is the traditional dividing
line between what I will call
low energy X-rays and high energy X-rays.
In other words, the
region where we've had,
before NuSTAR very
sophisticated telescopes.
NuSTAR is the first telescope to focus
and be sensitive above 10, okay?
And so, this has given us a
whole new view of the universe.
Now, I do wanna point
out here that we have
had instruments that
have viewed the heavens
in high energy X-rays, all right?
But they were very crude,
based on kind of pinhole cameras, right?
And if you've used a pinhole
camera, you know you use it
to look at the sun or very bright things.
It's 'cause it's inherently
not very sensitive.
That's what we had before.
Okay, so, I'm gonna use an
analogy here to try to explain
what you get by adding high energy X-rays
to our pallet of colors with
which we view the universe.
So, visible light is made of
colors and so is X-ray light.
So, low energy X-rays
correspond in this analogy
to red, yellow and green light.
Where the high energy X-rays correspond
to blue, indigo and violet.
All right, so you can think of NuSTAR
as adding these new colors
to the X-ray window,
and this is a visible
light image of a galaxy,
beautiful, called the
Antennae and on the left,
this is the image in black and white.
If you make the image in red and yellow,
what you're seeing is
you're seeing the cooler,
dusty regions of the galaxy, all right?
And then on the right,
if you add blue light,
what you're seeing is where
hot, young stars are forming
and blowing energy out into the galaxy.
And so, when you look in different colors
and add them all together,
again, what you're seeing
is regions with different
physical properties,
different temperatures and
so it's by bringing the full
range of colors that we get
this rich view of the universe.
Okay, so, using the same
color or energy, all right?
So, color corresponds to energy,
of X-rays that your doctor
and dentist use to image
your teeth and bones,
this is the same energy
that NuSTAR is using
to observe these hot, dense
regions of the universe.
And again, because high energy
X-rays are very penetrating,
that's why they're used for medical X-rays
'cause they penetrate
through your skin and image,
but are stopped by your bones.
They also penetrate through
dust and gas and illuminate
objects that are otherwise
hidden from view.
So, this is unlike the
lower energy X-rays.
So, these are some real
images of astronomical objects
where the red and green
are low energy X-rays
and the blue is what's
been added by NuSTAR.
So, you can see illuminating
and measuring temperatures
in the hot regions here,
you can see of sun.
The hottest regions are in these flares.
So, being able to focus
these high energy X-rays
took a lot of technology development.
Both new kinds of X-ray lenses or optics
and new kinds of detectors and this is,
you know, myself and my collaborators
spent more than a decade developing.
So, in this photo you can
see the X-ray detectors
that Eliot referred to.
These I started working on
when I was here at Berkeley,
and then when we built them
we actually collaborated
with people at the
Space Sciences Lab here.
These are kind of like
the digital detector
in your cell phone.
Only they have to made
out of special material
that can actually stop the X-rays.
X-ray mirrors look very different
than mirrors in the optical, all right?
So, we developed those also
for the NuSTAR mission,
and as Eliot said, we
built a lot of the hardware
in my labs at Caltech
and also up the hill,
go up Centennial Drive to the
top at Space Sciences Lab.
Giving the opportunity
for students in postdocs
to actually get their
hands on the hardware.
That's one of the great things about
these smaller NASA missions.
So, it was 15 years from the first serious
technology development to launch.
It was about four years to
actually build the mission.
So, this picture here shows you
the NuSTAR spacecraft, all right?
That was all put together
out in Dulles, Virginia.
And then we drove it across
the country to Vandenberg
where we put it in the rocket,
what's called the shroud.
So, you can see that on the right.
Then, it's a very unusual
kind of launch because NuSTAR
is a small mission, you need
an inexpensive launch vehicle.
So, the rocket was actually
mounted under the belly of
an L-1011 aircraft and what
I wanna point out here 'cause
this'll be important in a
minute, is that this right here,
the whole telescope has to
fit in that region, okay?
So, think about that relative
to the length of this L-1011.
Some of you may remember L-1011's, right?
Those were used, what, 40
years ago or something.
Anyway, so the airplane
took off from Vandenberg
and flew to Kwajalein
in the South Pacific.
Not for the palm trees, but
there's a reason you want
to go around the equator
that I won't go into,
and launched.
And it's a very
interesting kind of launch.
I wanna show you a video of how it works.
This is not actually the NuSTAR launch,
because NuSTAR launched at night,
so you couldn't see anything.
But, this is another launch.
(airplane roaring)
Same kind of launch vehicle
called a Pegasus.
So, what the aircraft does is it takes off
and gets to like 35,000 feet or something.
- One, drop.
- And then the rocket
drops for five seconds.
(muffled talking)
Ignites and actually launches in front--
- Stable.
- Of the aircraft, okay?
So, this happened
June 13th of 2012--
- Accelerating right on track.
Looks good.
- For NuSTAR, and then the
rocket goes into an orbit.
It basically goes into
free fall around the Earth.
So, it goes around the
whole Earth every 90 minutes
at an altitude of about 600 kilometers.
So, as it turns out, the
company that builds this,
it used to be called Orbital Sciences,
and the CEO is a personal friend of mine.
And I was actually the research advisor
for his daughter when she
was a high school student.
So, he said, you know what,
I'm gonna give you this great opportunity.
We rarely allow scientists to do this,
but we'll let you ride in the plane.
And I thought, great.
Take off with a ton of solid explosive
under me.
(audience laughing)
So, I didn't ride in the plane.
So, in fact, I was here at Berkeley,
up on the hill for the launch.
I mean, what's important?
So, NuSTAR launched at night,
but what's important is
after you launch, right,
it's nail biting minutes, right?
To see whether you go up or down, right?
And I wasn't particularly worried
about this 'cause I figured,
yeah it's gonna go up or down
and there's nothing I can
do about it, all right?
But I wanted to see that all
the telemetry that comes afterwards.
And you can see that's an infrared.
Remember I said warm things
are visible in the infrared?
Well, the rocket was warm and so you had
a infrared camera where we could see it.
So, in fact, it went up, which was good,
and it got into a 600 kilometer
orbit around the Earth.
And so, what my research
group at Caltech saw,
this is the actual NuSTAR launch.
(people cheering)
(people applauding)
So that's all, you know.
Okay, so, that's all I would have seen.
What I was worried about was
something that I did have more
to do with and that's what had to happen,
it happened about nine
days after launch, okay?
So, now if you remember I said,
remember how short that rocket shroud
is compared to the length of the airplane?
And if you think back to
that picture I showed you of
the Chandra X-ray telescope,
and the XMM telescope
and the NuSTAR telescope,
they're all really long, right?
They're about 10 meters, 33 feet,
the length of a school bus, okay?
'Cause X-ray optics,
that's the way they work.
You have to have a long distance between
the optic and the detector.
So, how does that happen?
Well, we sent a command to
the instrument and when that
command was received, what
happened is a TINKERTOY like
structure of about 100,000
piece parts started to unfold,
clicking into place one
piece at a time, all right?
So, this took a total of 24 minutes.
So, the Mars guys brag about their
seven minutes of terror, right?
This was 24 minutes of terror,
'cause I actually knew
that when we tried this
on the ground the first
time it didn't work.
And we never fully
deployed it all assembled.
But, it worked perfectly
and in fact locked
into place and NuSTAR's
two X-ray telescopes,
there's two of 'em pointing
at the same direction.
We just add the imagines, it's
just to collect more X-rays.
So, I wanna show you in
a very qualitative way
the advance that NuSTAR
has made in our ability
to view the high energy X-ray universe.
Remember I told you that
we've had these kind
of crude pinhole camera like telescopes
in the high energy X-ray band?
This is an image from one of them,
which is about four times the
diameter of the sun in area
of the sky by two times the
diameter of the sun, okay?
But it's centered on a very special place,
which is the heart of
our own Milky Way galaxy,
where there resides a few
million solar mass black hole.
All right?
And this shows you that with
these pinhole camera sources,
these big blobs, those are big just
because the resolution is very blurry.
It's a very blurry
telescope that can only see
very few of the brightest objects.
If we take one pixel in
this image and blow it up,
that's the field of view of NuSTAR,
and you can see all of
this detail that we can see
for the first time, all right?
And one of our first discovers, in fact,
was we noticed this haze,
blue haze around the center
of a supermassive black
hole in our galaxy.
So, it turns out that this
had never been seen before,
and what it is, it's a swarm
of dead remnants of stars
creating this haze and again,
it had never been seen before.
And I'm not gonna tell
you too much about how
we think they got there, but
we do take public outreach
very seriously on NuSTAR.
So, we had a press release
about this result.
(audience laughing)
And it's always interesting to see how
the press picks these things up.
I particularly like the
zombie stars aspect of this.
Anyway.
So, now let's talk about specifically
I'm gonna go into the science
of two of the results.
Hopefully two if I have the time.
The first is how NuSTAR has
been able to make the first
unambiguous measurement
of what's called the spin
of supermassive black holes
in the centers of galaxies.
So, first, let me tell you a
little bit about black holes.
What's a black hole?
Well, a black hole is a
rip or a tear in the fabric
of space time that happens
when you get enough matter
and you squish it into
a small enough volume,
then collapses to what physicists
refer to as a singularity.
And there's a region around the black hole
where not even light can escape.
And so, these black holes
are actually a prediction
of Einstein's theory
of general relativity.
They're not predicted
by classical gravity,
and Einstein himself actually thought
the solution was an oddity
and actually not really
corresponding to real, physical objects.
But now, we know in fact
from many observations,
including the discovery
of gravitational waves,
observations in the
electromagnetic spectrum,
that black holes do exist.
And this is actually not a
real image of a black hole.
This is just a simulation, okay?
Because if you wanted
to see in the optical
this event horizon or region
from which light can't escape,
you would have to have a telescope
with incredibly good resolution.
Something that we don't have now
and really can't envision having.
Now, you may have seen the press release
of the image of the black hole.
That was not in the optical,
that was in the radio.
I won't talk too much about it.
I'll mention it in a minute.
But at any rate, all sorts
of weird things happen around
black holes; they bend light,
all right, because of gravity.
Again, a prediction of general relativity.
But besides mass, all right?
Which determines the size of this
what's called horizon, all right?
Black holes have spin
and they acquire spin,
if the object that forms them,
let's imagine it's a
very massive star, okay?
That collapses, for example.
If that star is spinning, then
like the figure skater when
he brings in his arms, he
spins more and more rapidly.
As it collapses, it spins more rapidly
and then when it
collapses to a singularity
it acquires this thing called spin.
And this is something that
NuSTAR was able to measure.
All right, so, if no light can escape,
how do we actually quote
unquote, see black holes?
Well, black holes don't live
in isolation for the most part.
They live in galaxies that
are full of dust and gas.
And in some instances,
there's enough dust and gas
and conditions are right
that just the gravity
of the black hole attracts
this matter and as it falls in,
when it gets close it organizes
itself into a disk, all right?
And friction in the disk
turns the gravitational energy
into heat and as it gets closer and closer
it gets hotter and hotter and it radiates.
And in these regions, particles
get boosted very close to
the speed of light and all of
these processes emit X-rays.
And so, it's through this matter
falling on and lighting up
and emitting high energy radiation,
that enables us to find these
massive black holes in the centers.
So, the black holes in
the centers of galaxies
are millions to billions times
the mass of the sun, right?
They're quite common in
the center of galaxies,
but in a fraction of cases
this process is going on that
lights them up and we can
find them in the X-rays.
Now, I just wanna show this image
because you may be
confused by what I said.
You said, well, you told me
you couldn't image the event
horizon of a black hole, but
you probably saw this because
it was not only the most
downloaded astronomical image ever,
I'm told it was the most downloaded image
from the web period, ever.
Which is kind of an interesting thing.
But this was made with a radio
telescope showing a region
which is related to the event
horizon of a black hole.
That's very, very cool, but
it's only been done once,
for one object.
For the mast part, we
have to rely on looking
at the radiation from
these disks of matter
as it spirals in to the black hole.
So, this is an artist's conception
of what goes on very
close to the black hole.
So, you see this disk of
material that's spiraling on,
and I told you there were
regions where particles
get boosted to high energies, right?
These regions here emit X-rays.
And if we can use those X-rays
emitted from this region to
somehow tell us about the
nature of this disk of material,
we can determine the black
hole's spin, all right?
And I'm gonna explain how
this happens, all right?
If you don't completely
follow it, that's okay.
You'll get to the punch line.
But basically the way it works
is this like a flashlight.
It shines down and reflects
X-rays off this material.
By looking at the X-ray
light that is reflected off
of this material, we can
tell how close this disk
of material comes to the
black hole, all right?
And how close it can come, all right?
So, it turns out, again, if
your sorta physics one or two,
you know that in classical
gravity you can have a particle
orbiting a body at any radius
in a stable orbit, right?
But around a black hole,
where general relativity
is important, there's
a minimum stable radius
and that depends on how fast
the black hole is spinning.
So, if it's not spinning at all,
it can't come all the way close to it,
it can't come as close to the black hole
as if the black hole
spin is in the same sense
as the material is orbiting
as it falls on, okay?
And so, it's this that
we're trying to measure,
and you can do this with X-rays.
Basically, what I'm showing
here is the brightness
of X-rays as a function
of the color or energy,
where this is blue or this red here.
Remember I said to
remember the number 10 as
the dividing line between low
energy and high energy X-rays?
Okay, so you can see the shape
of this intensity of color
is all the way from red
to blue, to very blue.
It's very different if this material comes
all the way close to the black hole,
and this has to do with
effects I won't go into,
related to the distortions,
the velocity with which the
material rotates and distortions
do to general relativity.
So, it's this measurement that
we use to measure the spin.
Now, if you're thinking, you're
thinking well wait a minute,
you told me that Chandra and
XMM, these telescopes that
we've had for years measure
the spectrum up to 10, right?
So, how come you can't
just use that, okay?
Well, it turns out there's
a confounding factor that
there's lost of dust and gas
around these black holes,
I already told you that.
That's what actually forms
this disk of material.
And if the X-rays have to
travel through dust and gas,
it can change the way that
its intensity of colors looks
and make it look really exactly like
the gravitational distortion,
the material coming very close.
So, people for a long
time argued about is this
a spinning black hole or is it
just dust and gas, you know?
And this was a lot of
uncivil conversations
at conferences for many
years about whether
we were really seeing a black hole spin.
But when you add the blue
colors or that NuSTAR colors,
then the case where the
black hole is spinning,
okay here, that shape,
just focus on the shape,
looks very different than if
you just have a lot of dust
and gas obscuring it, right?
So, it's this difference
suddenly that enables us to this.
And so, this was one of
the first observations
that NuSTAR made.
We decided to look at
a particular black hole
in a galaxy called NGC
1365, by the way, all right?
It's about a two million
solar mass black hole,
and we decided to use XMM-Newton, okay?
Look at the red colors at
the same time with NuSTAR,
and actually this is known
to be a very dusty galaxy
and what we actually wanted to look at
was clouds of dust and gas.
We thought, won't that be cool?
We'll see this dust and
gas moving around, okay?
And so, one of the first
conferences I went to after launch
my collaborator, Guido, who
was looking at the XMM data
and I, decided to meet at the bar
before the conference, okay?
And he said, okay, this is what I have.
So, here's the blue points
from XMM, the red colors.
And again, this is brightness or intensity
as a function of the color of X-rays.
And if you don't quite
understand what that means,
don't worry, again, you'll
still understand the point.
Which is that this is
a model in green where
the black hole is spinning,
it's a very high spin.
And this one where there's
just a lot of dust and gas.
And he said, well they can't
really tell the difference,
and my student had been analyzing
the NuSTAR data and I pulled it out
and I sort of laid them
on top of each other.
And there's the NuSTAR data, okay?
So, clearly indicating that
this black hole is spinning
actually quite close to the
fastest rate that's allowed
before it would essentially fly apart.
We call this maximally
spinning black hole.
So, this was pretty cool and
convinced 90% or maybe 99%
of the community, all right?
And so, we had a big press release,
'cause you wanna get your results
out to the public about this,
and it was a great press release.
But afterwards, a bunch
of reporters called me up
and they said, well you
didn't say exactly how fast,
like in miles per hour,
this black hole is spinning.
(audience laughing)
And I said, well, you can't
really paint an X on the,
you know, there's no fiducial
mark on a black hole.
You know, I'm trying to explain this
in an understandable way.
So, you can't really watch how
fast a mark is going around,
and it's not really a right
way to think about it.
And they said, well you
have to give me some speed.
Like, you know, okay, so
how fast is it rotating
in rotations per second?
I said, well you can't really paint
an X on a black hole.
(audience laughing)
So, then I thought, oh,
well maybe here's a way.
I said, well look, okay,
so, spinning black holes,
one thing that they do,
which is one reason why
this material can come closer,
is they literally drag space and time
around with them, okay?
So, I said, okay, so if I'm an
observer near the black hole,
I would have to rotate
15 times per minute,
as viewed by an observer at
infinity just to stand still.
They said, well that
doesn't sound very fast.
So, then I finally came up
with the following, okay?
With the mass of this black
hole and how fast it's spinning,
if I grabbed it and stopped it,
I could get enough energy
out of that black hole
to unbind all the material in the galaxy.
And that's what lead to the doomsday
black hole story in space.com.
(audience laughing)
Okay.
All right, so now I'm gonna tell you about
our first journal cover, okay?
And that's actually our
first and only journal cover.
It was the Sedona Journal
of Emergence, okay?
And my postdoc was,
there's a famous bookstore
in Pasadena called Vroman's
Bookstore and astrology
is right next to astronomy
'cause the magazines
are all in alphabetical order.
And so, this is actually one
of our first press releases
of a very famous remnant
of an exploded star
called Cassiopeia A.
If you can't read this
red text here, it says,
"This new view of the historical supernova
"remnant Cassiopeia A located
11,000 light-years away,
"was taken by NASA.
"Inside, Cassiopeia speaks
through Robert Shapiro."
(audience laughing)
Now, I don't actually know
what Cassiopeia A said,
'cause I didn't read the
article, but um, anyway.
We might have got readers than
the astronomical journal for that one.
But, with NuSTAR, so, now let
me tell you about what we've
learned about the explosions
of massive stars with NuSTAR.
And let me step back just a
minute and remind you that
the universe started as a soup
of hydrogen and helium that existed,
and a little bit of lithium that existed
shortly after it was born.
And today, 13.8 billion years later,
after this hot homogenous
universe was created,
we have a rich mix of chemical
elements from nitrogen
in the atmosphere to
calcium in your bones.
What you're seeing here is
a theoretical simulation
of filaments of hydrogen and helium shaped
by the gravity of dark matter, all right?
Forming galaxies in the dense regions,
and in these galaxies, stars
form and the massive stars
burn through their fuel and they explode.
These stars are creating elements
and spewing them out into
galaxies and the region between
galaxies when they explode.
And this is how the elements
or many of the elements
are forged and then
distributed in the universe.
So that they can create,
condense into galaxies,
stars, planets and life.
So, this, I mean it's
a beautiful simulation
and it's based on governing principles.
What scientists think is reasonable,
but many of the key components
still have to be verified observationally.
How it works in practice,
there's still an awful lot
of observational work to do.
And one part of this observational
work is to understand
how these massive stars actually explode.
So, these images show
you that this process
of massive stars exploding
in a little more detail.
So, stars are basically big
nuclear fusion reactions.
Like a hydrogen bomb, all right?
But much more controlled and
with these controlled reactions
they burn hydrogen and
helium into carbon, oxygen,
silicon and eventually iron, all right?
But after enough of
the star burns to iron,
you can't create more heat to keep
the star from collapsing, all right?
Because it's a detail of nuclear physics,
and once you get to iron,
you can't create energy from fusion.
So, what happens is the
core of the star basically
collapses and bounces and explodes
the star apart in what's
called a supernova event.
And then, this sends a
blast wave plowing out into
the medium around the star,
which heats this medium
and it glows in what's
called a remnant for hundreds
to thousands of years
after the explosions.
So, these stellar explosions
I've already mentioned,
even though it's a small
fraction of all stars,
they're very important for creating
the elements and life itself.
But, how stars actually explode
has been a profound mystery.
It turns out that it's really,
really hard to make something
that's imploding very fast,
explode and blow apart, all right?
And stellar explosions
have some similarities
to atomic bombs and similar to bombs,
huge computational power
and theoretical resources
have gone in to trying to understand 'em.
And until recently most
computer explosion models
couldn't actually make a star explode.
Especially if they tried to do it
in a spherically symmetric way.
And even today to make stars explode,
computer models have to
add theoretical ingredients
that still have to be
verified observationally.
So, what you see here is an example of one
of these computer codes, all right?
That can make a star blow apart.
And the way this happens
is that the computer code
puts in instabilities or
essentially what we call
sloshing of the core
of the star, all right?
Which does work, adds energy and helps
make the star explode.
But, is this really what happens?
Well, you need observations
to determine that.
There are other ways
to make stars explode.
One of them is to have
the star rotating rapidly,
in which case it'll explode
in a very different way.
Instead of a sort of
sloshing around, all right?
It'll create this very
elongated type of explosion.
Which again works, but we
wanna try to understand,
maybe all of these kinds of things
are happening for different stars.
How do we determine observationally
what is making stars explode?
So, kind of like with
the black holes, right?
The supernova event itself,
first, it's pretty short, okay?
It doesn't, it explodes pretty quickly,
and we don't have telescopes
with good enough resolution
to actually watch like this
theoretical model I showed you,
what's going on in the explosion.
So, how do we learn about
supernova explosions?
Well, we can study the light
that you see shortly after
the explosion and how that evolves.
That what Alex Filippenko here does.
But another thing that
you can do is you can hope
to learn more about the
explosion by studying
what's left over afterwards.
And so, previous low
energy X-ray observatories
have taken pictures of the
remnants of supernova explosions
that happen, you know,
these pictures are hundreds
to thousands of years after the event.
And you can that these
are incredibly beautiful.
I mean, just look at them.
These are real images, okay?
These are not theoretical models.
I like to make the analogy
that it's sort of like
a crime scene investigator
who looks at the shrapnel
and other debris after a
bomb explodes and tries
to figure out how the
explosion happened, all right?
So, astronomical telescopes
try to piece together
the workings of the bomb
from images like this.
And what low energy telescopes
have been able to look at,
is the hot glow from the
debris of the explosions
because it's hot and it's
heating up, you know,
the blast wave is heating
up material, all right?
However, what they're seeing
is the very outer layers,
or if you like, the casing
of the bomb, all right?
They're not actually
seeing the inner workings
of the explosion itself, all right?
So, what NuSTAR has done is
add, sort of given a new CSI,
a new analytical method, right?
Okay, so, it's providing us a
completely new tool with which
to look at these remnants
of exploded stars.
It's seeing the radioactive shrapnel.
Instead of the hot material,
the radioactive shrapnel.
Which you see when chemical
element changes into another.
So, when titanium changes into calcium.
This happens on a very
short timescale on cosmic,
in a few hundred years
the radioactivity is gone,
but if you can look at young remnants,
what you can do is use
this radioactive material
to see the inner workings
of the bomb, okay?
As opposed to how the
casing gets distributed,
which depends on a lot of
things like the material
into which the bomb is
exploding, all right?
So, here are images of the historical
supernova remnant Cassiopeia A.
These two are made in low energy X-rays
by the Chandra X-ray telescope.
And if you tried to use the
shape, so we're trying to use
the shape of the explosion
to determine what happened.
Here, this is kind of blobby and the blobs
are sort of symmetrically distributed
the way that sloshing model looked, okay?
Whereas this one is elongated
like the rotating star model,
and people have used these to
argue somewhat more civilly
than in the case of the black holes,
about whether this was a
rotating star mechanism
or a sloshing mechanism.
But when you look at the radioactivity,
you see the true shape
or nature of the material
and its distribution that
was in the explosion itself.
And without going into more detail,
the shape is very
indicative of what happens
in the sloshing model.
So, when you put it all together,
this is Cassiopeia A in its
panchromatic glory here with
the NuSTAR radioactivity and
then the hot glowing embers
in green and red from Chandra.
And I wanna say science is
a wonderful thing, okay?
Because before launch, you know,
we'd put a lot of work into
designing NuSTAR to be able
to observe this radioactivity, okay?
But I had a bunch of theorists
tell me I was wasting my time
because everybody knows
that this radioactivity
is gonna be distributed exactly the way
that glowing iron is in the red, okay?
But you can see there's really no,
I showed this, my daughter
was five at the time and said,
"Joanna, do these look the same?"
And she said, "are you kidding?"
(audience laughing)
So, it's a mystery.
We don't really quite understand this,
but something new to study
and I'll end just by saying
that we launched in 2012.
For two years the science team controlled
the mission and did these observations.
Since then, we've been
giving the community access
to NuSTAR so anybody, you
could write a proposal
to use NuSTAR to look at something.
We're now, again, it's
2019, we just got renewed
by NASA for another three
years of observations.
So, I think there's a lot more
of exciting stuff to come.
Thank you.
(audience applauding)
- [Student] A few questions.
What is the horizon for NuSTAR in terms
of its propellant and
being able to aim it?
And the other is have you
or do you expect to discover
any black holes with
retrograde accretion disks?
- Those are both great questions.
So, first off, NuSTAR
doesn't have any propellant.
So, it really has nothing
that's expendable.
The orbit will eventually decay.
Now, it is a small mission,
and so, the big, expensive NASA missions
have two of almost
everything that's critical.
We have one of almost
everything that's critical.
So, something could break.
But other than that, the orbit should last
for another 10 or 15 years.
And then the question
about retrograde motion
is a really good one.
And that...
So far there are no observations
that securely show a material orbiting
in the opposite direction as
the spin of the black hole.
And we think in part, the
black hole spin can be acquired
from the direction that matter, you know,
if it consistently orbits
in the same direction
and falls onto the black hole,
that can make it spin faster.
So, it'd be quite interesting if you saw
you know, if the disks
switched direction over time,
just 'cause of the way
the matter is falling in.
That would be quite interesting
because it would say
something about on average
whether black holes acquire spin
or looking at it the other
way if you measure the spin
of a lot of black holes, that
tells you something about
how the matter falls on
over long time scales.
- [Student] So going back to my, actually,
I'd like to go back to my first
question, how do you aim it?
- So, the way we aim it is
we have magnetic torque bars.
So, you put a current through
a bar that creates a magnetic
field that twists against
the Earth's magnetic field.
So, we don't actually
have to use propellant.
- [Student] When observing
these events that happen over
very short periods of
time; hours, days, weeks,
do synchronicity of observation
at different wavelengths
and even with gravitational
now and particle telescopes,
to what extent is that a
matter of mere logistics
and arm twisting among people
who control telescopes built
on completely different
operation premises?
And how much is science
and how much can we see
in the future in terms
of hybrid observatories?
- Yeah, that's actually a great question
because we learn so much.
You know, imagine we have
a very wide field optical
telescope that can say, oh,
something exploded over here.
You get the most information if everybody
can quickly look, right?
And like you say, until, you know,
I used to work in the
field of gamma ray bursts
and I saw Josh Bloom here
earlier, he did too, right?
So, he can tell you, right, over a beer,
how hard it was to call
somebody up and say please,
you know, something
interesting is going on.
Can we please look over here?
But we're really now because of LIGO
and better wide field telescopes,
we're in this era of
what's called time domain,
where there's a huge community effort
to try to make these
quick observations happen,
because the scientific return is so great.
And you mentioned the gravitational waves.
This is huge, right?
I mean, you may have heard
of the single merging neutron
stars where we detected
everything from gamma rays
all the way to radio and we
learned so much about how,
you know, elements like the
gold in your wedding ring,
platinum are formed,
about energetic processes.
So, we do live in this age where everybody
is trying to make it easier.
And so, one thing NuSTAR
is doing and it's old age,
is we're trying to become more agile.
So, we're working with the
people up on the hill at Berkeley
to be able to point more quickly
and respond more quickly.
So, yeah, it's a great question.
- [Eliot] Do you have a question?
- [Student] Why does NuSTAR
appear to be much longer than
the telescopes that are
used to locate infrared.
- Also a good question.
All right, so, now I get to talk about
the hardware a little bit.
Which I could have given
another entire lecture on.
But, so the way that
X-rays reflect, all right?
So, they don't, if you
make a lens, you can't make
an X-ray lens very efficiently
because when they go into
material they only bend a tiny little bit.
So, you have to reflect
them and they only reflect
at incredibly small angles
or glancing incidents.
So, it's kinda of like skipping a rock off
the surface of a pond, right?
You can imagine it
bouncing off the surface
and then it comes to
a focus very far away.
And so, you need to have
a very long distance
between these reflecting
surfaces and the detectors.
So, it's just inherently
the way X-rays reflect,
the physics of how they
reflect off of materials.
- [Student] Is there a next generation?
And how will it improve
upon the characteristics?
- Well, probably not surprisingly,
astronomers are never satisfied
and we are thinking about
a next generation version
that would have better,
so, NuSTAR, I told you it
made images that are hundreds
of times crisper, better resolution.
But it's still, compared to
what you can do in the optical
or even with the Chandra
low energy X-ray telescope,
you know, we can still improve
on that by factors of many.
So, we're thinking about how
to do that and if we could make
a larger telescope launched
on a bigger platform.
But that's years away.
You know, I think we've gotta
develop the technologies
and then convince NASA to do it.
Was that the end of your question
or did you have another part?
Yeah, so, the technologies
really are based on being able
to build mirrors that
are much more precise.
- [Student] I had a hardware question.
When I saw those four devices
that made up the detector.
- Mm hm.
- I was wondering
what it is that can stop a
79 kiloelectron volt photon?
So, are those area photon
counters kinda detectors?
Is that sorta what
it's been imaging?
- Yes.
Right, so, they work kinda
similar to the what are called
the CCDs, silicon detectors
in your cell phone camera,
but you have to make
the material much better
at stopping high energy X-rays.
So, we actually make the material,
it's called cadmium zinc telluride.
- Okay.
- All right,
but it's a kinda material
that's very dense
and very able to stop high energy X-rays.
So, we have to manufacture
the detector out of that,
and then the part that reads it out
is made out of the silicon.
And there's four of them in the detector
just because there's a limit
on the fabrication process
on how big you make one detector.
So, we just put four in an array
to get the size that we want.
- [Student] Can you
talk about the decision
to point NuSTAR at the
sun and how you were able
to handle that dynamic range.
- Don't get me going on this, okay?
So, NuSTAR has been incredibly
reliable, all right?
The only two anomalies that we've had
is when we tried to point at the sun.
So, the reason, why would
you ever point at the sun?
You know, the sun's a
bright source of X-rays,
NuSTAR was built to be very sensitive.
Well, it turns out that
there's a big mystery,
which is the corona of
the sun is very hot,
the photosphere is colder
and so, how do you heat,
you know, the corona is this hot,
tenuous plasma further
out, how do you heat that?
And one idea is that you have
tiny, tiny little flares,
you know, called nanoflares
going off all over the place,
injecting energy in a uniform way.
And so, NuSTAR is uniquely
able to look to find these.
So, after the primary mission,
after we submitted our report
and got the letter from
NASA headquarters saying,
you officially accomplished
all of your primary goals.
You're a success.
So, well, why not try
to point it at the sun.
(audience laughing)
There's nothing technically
that stops us from doing
it and there's nothing else
you know, existing or
planned that can do this.
So, you know, that's why
we did it, for the science.
But it turns out, and this is a kind of
a techno nerd story,
but I'll tell it anyway.
It turns out that the coordinate
system that we use to point
NuSTAR has a singularity and
the equation's at the sun,
at the position of the
sun because who would ever
wanna point a telescope at the sun, right?
And so, the first time we tried
to point we were like, oops.
And so, then we kinda
found a way around that.
But we now can point at the sun,
but it was a learning experience.
I will say the other thing by the way,
which I find fascinating
is we can actually
test theories of light dark matter,
low mass dark matter
by looking at the sun,
because there's an effect
where the sun's magnetic field
can turn these dark matter
particles into X-rays.
And if you see a glow of X-rays
in the right energy range
from the sun, you can
actually detect dark matter.
Which I also find fascinating.
That's not why we did it
'cause I thought that was such
a long shot, but it's kind of interesting.
- [Student] I was wondering what
the field of view of NuSTAR is?
And as a follow up, if
it can be used to do like
a general survey of the
entire celestial sphere?
- Yeah, so, the field of
view is pretty narrow.
It's 12 minutes of arc on a side.
Which means it's really not very good
for surveying large regions of the sky.
You know, we sort of
surveyed maybe a regions,
a degree on a side sort of laboriously.
So, it's not designed.
There are ways to design
X-ray telescopes to have
a wider field of view, but
it makes 'em less sensitive.
- [Eliot] So, we have to wrap up now.
But please join me in thanking
Fiona for a wonderful talk.
(audience applauding)
(light music)
