Science in the Media
Session 3: Press Conference Video Transcript

Lynn Chandler:

Okay. Good morning and welcome to the NASA press conference on the
latest scientific discoveries from the Suzaku mission. I am Lynn
Chandler and I am the press officer for the Suzaku mission and today
we have with us Dr. Kim Weaver, Astrophysicist and Dr. Koji Mukai,
Suzaku Guest Observer Facility Lead. And at this time time I would
like to turn it over to our scientists for their presentations.

Dr. Kim Weaver:

Thanks Lynn. We’re discussing a new result from the Suzaku X-ray
satellite. For the first time, individual clouds of gas have been
caught in the act orbiting a giant black hole at the center of the
galaxy, this galaxy is named NGC 1365.

The movements and shapes of such clouds have long been a mystery to
astronomers. Remarkably these clouds have a shape similar to the
comets that we see in our solar system. These clouds can also tell
us a great deal about the extreme environments near black holes.

The science technique used to study these clouds is called
occultation or the blocking of x-ray light by the clouds themselves.
An occultation is when an apparently larger body passes in front of
a apparently smaller one. This happens, for example, when we see the
moon pass in front of a star as it orbits the earth.

With Suzaku, we have an occultation of a black hole by orbiting
clouds of gas. This is only the second time in occultation in x-rays
has been tracked so closely as to capture movements so near to a
black hole, but it’s the first time such unique dimming of x-ray
light has been seen that contains enough information to actually
determine the shapes of the clouds themselves that make up the x-ray
curtain in a galaxy.

Koji will now tell us about Suzaku and its importance for this
science, Koji.

Dr. Koji Mukai:

Thanks Kim.

Suzaku is an x-ray astronomy satellite built by a collaboration
between Japan and the U.S. and launched in July of 2005.

You may not have heard of Suzaku before. If you heard about one
x-ray astronomy mission it’s likely to be Chandra, which is
justifiably famous for the exquisite x-ray images that it can
capture, but there are other x-ray astronomy satellites in orbit
today.

So why do we need more than one x-ray astronomy satellite? This is
because it takes a lot of resources to build one satellite that can
do everything that an x-ray astronomer would ever want to do. It
makes sense for each project to focus on different aspects of x-ray
astronomy and build a satellite that can do that aspect very well.
In the case of Chandra it was the fine imaging ability. In the case
of Suzaku, the team decided to focus on spectroscopy.

Spectroscopy is the study of intensity of electromagnetic radiation
– visible light, x-rays and so on – as a function of its wavelength
or the energies of individual x-ray photons. One particular way that
Suzaku excels is that it covers a wide range of x-ray energies.
Suzaku has one type of instrument that can detect x-rays of the same
energies that Chandra can study, but Suzaku carries another
instrument which studies higher energy x-rays. So it’s like seeing
all the colors of the rainbow with Suzaku instead of just seeing
oranges and reds.

It also happens that higher energy x-rays bluer photons, so to
speak, penetrates deeper into gas clouds and lower energy x-rays
tend to get more absorbed. You can say that we use Suzaku and the
supermassive black hole to “x-ray” the gas cloud orbiting around the
NGC 1365, much like doctors do with your bones which is actually
quite rare in x-ray astronomy. This needed the Suzaku’s ability
to study x-rays, wide range of x-ray energies.

Another reason that Suzaku was essential for this study, was that,
we tend to stare at one object for a long time to build up the x-ray
spectra because you need to collect enough photons at each energy to
have a good spectrum. With short observations we would have missed
some of the important moments of this occultation event, so that was
another reason why Suzaku was important.

I hope I’ve made it clear why Suzaku was a great tool for this
research. I will now turn it back to Kim who will explain the
significance of this scientific discovery.

Dr. Kim Weaver:

Thanks Koji.

The black hole we are talking about is about two million times the
mass of our sun. As material comes close to the black hole it heats
up to about millions of degrees and gives off x-rays.

Obscuration of x-rays by dense gas is seen in many galaxies but
actual occultation by clouds themselves are rarely caught. One
reason is that a galaxy must be observed for a long time,
uninterrupted. It can be very hard to schedule such a long block of
time on our telescopes but it does happen. This particular
observation was three and a half days long, quite long.

The graphic currently being shown, shows the intensity of x-ray
light with time that was measured from this galaxy, and you can see
a lot of variability in the x-ray light.

Suzaku saw two distinct eclipsing events marked by the green lines.
As you can see for each eclipse there is a sudden dimming in x-rays
due to the transit of a dense cloud covering about sixty five
percent of the x-ray source.

The specific variability of x-ray light in NGC 1365 was fairly easy
to find due to the way in which the galaxy is actually tilted with
respect to how we see it. The tilt, is pretty high tilt, gives us a
high chance of seeing through many clouds. Other galaxies could be
tilted differently so it could be very hard to catch views of their
clouds. It’s possible that the events like this are simply very rare
for astronomers to witness.

The next graphic shows side-by-side pictures of an artist concept of
the comet like cloud passing in front of the black hole. A fast fade
out of light, like we saw in the light curve before means that the
dense cold cloud has to have a sharp leading edge as we see here. On
the left hand side you can see the dense cloud blocking the black
hole itself.

Slower dimming of the x-ray light over longer time indicates less
dense gas streaming out behind the dense cloud like the tail of a
comet, and you can see on the right hand side of the graphic now the
comet part of the cloud is passing in front of it.

The cloud geometry can be roughly sketched out. Scientists can only
reconstruct the shape of the tail projected on to the plane of the
sky; they can’t actually determine the shape of the cloud along our
direction.

The next graphic shows the comet cloud in relation to our solar
system, in relation to the sun earth distance. The length of the
cloud’s tail covers a distance at about the same as that between the
earth and the sun and as you can see here in this artist concept. As
these clouds orbit the black hole, they constantly loose mass and
the expected lifetime of an individual cloud is only two months.

Where does the gas go that is lost? It’s probably not accreted or
eaten by the black hole. It either heats up to ten million degrees
and becomes part of a hot haze of gas that the clouds have to pass
through, or the gas lost is caused by radiation pressure for the
black hole and the gas becomes part of an out flowing wind. About a
tenth of a solar mass per year, which is many clouds worth, could be
lost this way.

What are the clouds? This is unclear. Atmospheres of start can
produce mass loss that resembles tails but they are not nearly
enough starts here to account for the number of clouds that are
seen. The dense clouds are probably moving supersonically through a
less dense haze. This would set up a system of shocks, like bow
shocks. As the dense clouds plow through the regions of hot gas, the
clouds erode, and the erosion creates the tails. Is a comet shape
common for such clouds? Well that’s not known. We need more
observations of occulting events like this to understand these and
other questions.

Lynn Chandler:

Thank you Kim and Koji.

And that concludes our presentation portion of the press briefing
today, and at this time we’re going to take questions.

We do have some callers on the phone and I ask that you specify
which scientist you would like to answer your question. And our
first caller is from Jeffrey a student in California.

Jeffrey:

This is for Dr. Mukai. What information does the Suzaku mission
seek to discover? And what are the most important purposes of this
probe?

Dr. Koji Mukai:

Well one answer to this question is that Suzaku is a facility for
the entire astronomical community. So the community decides what
questions toto tackle and what objects to observe and so on. But we
did have some overarching goals for the mission, when we built the
mission. One is we’d like to study how various chemical elements are
formed in the universe, and how they’re dispersed. Another focus
area is the study of matter under extreme conditions such as these
clouds right near black holes.

Lynn Chandler:

Okay. And our second caller, Lauren is a student from Texas.

Lauren:

This is for Dr. Weaver. How large is a supersize black hole? What
would a normal size black hole be like?

Dr. Kim Weaver:

A normal black hole would be the most common type that we see which are
stellar mass black holes. A black hole that has the mass of about the
mass of our sun would be about three miles across, so it would be
very small, very tiny.

A supersize black hole can be much, much larger and range from with
sizes anywhere from a tenth of a distance between the earth and the
sun to as large as our entire solar system put together.

Lynn Chandler:

Okay. And our next question comes from Bailey in Michigan.

Bailey:

This is for Dr. Weaver. Approximately how big is the black hole’s
diameter, and are there black holes bigger than this one?

Dr. Kim Weaver:

Yes. There are black holes bigger than this one. There are many in
fact, you can a have black holes with masses that are up to a
billion times the mass of the sun, so one hundred times more massive
than this black hole. And a black hole like that would be about one
hundred times larger, and again that would be roughly the size of
our solar system.

Lynn Chandler:

Okay. And our next question comes from Brittney in New York.

Brittney:

For Dr. Mukai, why is Suzaku called the red bird of the south?

Dr. Koji Mukai:

That’s a very interesting question. The first x-ray ray astronomy
satellite launched by our Japanese colleagues was called
Hakucho,which is the Japanese name for the constellation Cygnus or
swan. So that started the tradition of naming the x-ray astronomy
satellites after flying creatures. The fourth one was called ASCA,
which was an acronym but also meant a flying bird and it also was
the name of an ancient Japanese era. So for their fifth x-ray
astronomy satellite they picked Suzaku, which not only means the red
bird of the south, but it’s also a name of another era in Japanese
history.

Lynn Chandler:

Okay. And our next question comes from Madeline a student from
Louisiana.

Madeline:

This is for Dr. Weaver. In what ways are clouds detected around the
black hole comparable to those observed in our own solar system?

Dr. Kim Weaver:

Well clouds in our solar system are like the clouds that we see in
our earth’s atmosphere. So the way in which their similar; when you
look up in the sky and its a cloudy day, the clouds are blocking the
suns light form us to see, these clouds are similar in that they are
blocking the x-ray light in the galaxy.

Lynn Chandler:

And our last question today comes from Andrew in Virginia.

Andrew:

This one is for doctor Weaver. What’s the importance of this finding
for astronomy?

Dr. Kim Weaver:

Well Koji mentioned one importance and that’s understanding the
extreme environments around black holes, but another thing that’s
really interesting about this is that black holes generally are
thought of as gobbling up material that comes near them, and eating
stuff that flies by, never to be seen again. But in this case we’re
actually understanding material that’s going to be going away from
the black hole, being pushed away from the black hole in an
out-flowing wind. So we’re using this experiment to understand
things that move away from the black hole and thus are apart of the
entire system of the black hole galaxy environment.

Lynn Chandler:

Okay. Thank you for joining us today and this concludes our NASA
press briefing on the Suzaku mission.





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