Christian Ready: The James Webb Space Telescope just released a
spectacular new image of the debris disc around the star Fomalhaut.
Astronomers used Webb to search for Fomalhaut's inner asteroid belt, but
instead it found not one, not two, but at least three nested belts around the star.
Fomalhaut was observed before at wavelengths ranging from visible light
with the Hubble Space Telescope all the way to the microwave spectrum with ALMA.
Hubble used a coronagraph to block out the light from the star to reveal its
outer debris ring, and that gave the image this really cool "Eye of Sauron" vibe.
At millimeter wavelengths, ALMA detected the outer ring as well, and
this outer ring is the equivalent of the Kuiper belt in our solar
system beyond Neptune's orbit.
So a team of astronomers used Webb to see if they could locate
Fomalhaut's equivalent of our solar system's asteroid belt, which should
orbit a lot closer to the star.
That alone would've been a really cool discovery because it would've been the
first detection of an exo-asteroid belt.
But what they found instead was more like an extended asteroid
disc that was surrounded by an even more unexpected intermediate belt.
The observations were made with Webb's Mid-Infrared Instrument
or "MIRI" by a team led by Dr.
András Gáspár of the University of Arizona, and their results were published
today in the Journal Nature Astronomy.
So I was very happy to speak with Dr.
Gáspár and two of his collaborators, Schuyler Wolff and George Rieke,
who also just happens to be the MIRI science team lead here in the U.S.
We talked about how these results may represent evidence of multiple planets,
some nerdy details of planetary system formation, what happened to the former
exoplanet Fomalhaut b, how the MIRI images were created, and even some additional
images that NASA didn't release!
So I invite you to get nerdy with me as we learn more about the Rings of Fomalhaut.
Thank you all for joining me today, and congratulations on your result.
And am I seeing what I think I'm seeing?
I think I'm seeing two, maybe three asteroid belts.
Is that right?
Andras, you're the, uh, lead author of the paper.
Let's start with you.
András Gáspár: Hi.
Thanks for having us, uh, here.
Uh, I would put it slightly differently.
The Asteroid belt is quite well-constrained within
the solar system, right?
And we define it as being at a certain thermal location around the Sun.
And what we are seeing here is a more extended system with an outer
belt roughly at the same thermal location as where our Kuiper belt is.
It also has a component very close to Fomalhaut, which is a sort of
an analog to our asteroid belt.
What's really neat is that this asteroid belt component is way more extended
than we have in the solar system, and we've also discovered this very
narrow intermediate belt in the system.
So it's slightly different than what we anticipated just based on
thermal signatures from previous observations for the system.
George Rieke: So if I can break in, I think it's more than slightly different.
I think it's really different from what we anticipated because
all the previous images showed nothing inside that outer belt.
I mean, there's a great ALMA image, there's a great Hubble Space Telescope
image, and there's nothing there!
And so this is the fun of the new capability that you
could go look at something
and you go, "wow, I never knew it would look like that!"
And to me, that was the impact this had.
Christian Ready: Well, you're right, it is certainly very different than anything
that, uh, certainly I've ever seen, let alone anything you've ever seen.
But what were you hoping to learn about when you used
James Webb to study Fomalhaut?
What were your science objectives for this program?
András Gáspár: So the primary objective of this program was to
observe three different systems.
The three systems were Fomalhaut, which you see results of right now,
Vega, and Epsilon Eridani.
The Vega and Epsilon Eridani observations are gonna be coming up this summer,
so we haven't seen those yet.
And the primary objectives were to see where the asteroid valve
components are located and how they look like within these systems.
We knew from thermal signatures, so there has to be some material at similar thermal
locations that we have in the solar system, but we didn't know for certain
where they are and how they're spread out.
Christian Ready: You mentioned thermal locations.
What, what do you mean by a thermal location?
Exactly?
Schuyler Wolff: Fomalhaut is a much younger, hotter star than the
sun, and so you get dust that's the same temperature as dust in our
own asteroid belt at wider radii.
Which allows you to see structures closer in thermally to the star than you would
in something like our own solar system.
Christian Ready: So do you think that that's what you're seeing here, you're
seeing the equivalent then of an asteroid, uh, probably a more rocky population,
closer to the star, and then a more icy population further from the star?
Schuyler Wolff: Probably, yes.
Another way to think about it is the asteroid belt is located at
sort of the transition between the terrestrial and the giant planets.
Whereas the Kuiper belt is outside the giant planets, all of the
material has been sort of pushed out as the outer planets migrated over
the lifetime of the solar system.
And so we're not just learning about the composition of the dust
in the various belts, but also hopefully something about the
history of the planetary system around Fomalhaut.
George Rieke: And to pick up on the thermal point, Fomalhaut is 16
times more energetic than the sun.
And because the intensity of light drops off as the square root of the
distance, that means you'd expect an asteroid belt at about four
times farther out around Fomalhaut.
Which would put it at about eight astronomical units, and that
would be right at the very inner edge of right at the black thing,
which is where things saturated.
And so what we expected was to just barely eek out a ring right at that
inner edge, and then not see anything from there until he went out to the
outer Kuiper belt-like ring that had already been, uh, seen so dramatically.
And, and so you could see how shocking this image was compared with what
we thought we were looking for.
Christian Ready: You've mentioned that this star is a lot younger than our son.
Do you think this is like a recently formed star, perhaps that it still has
some of its residual material, or is this something that's actually right here in
our solar system, but because we don't have infrared eyes, we don't see it.
Schuyler Wolff: It's younger than the sun, but it's still relatively old.
We still consider it to be in the debris disk phase.
So these are the debris of sort of the planet formation process.
This was another reason why we're quite surprised at what a bright
central source we have here.
András alluded to this before, but we have upcoming observations of Vega
and Epsilon Eridani, and the thing I'm most interested in is to see
how diverse planetary systems are, because this looks nothing like what we would
expect based on our own solar system.
So is it our own solar system that's unusual or is this the unusual case?
We don't know.
Christian Ready: I see.
So this is a, a phase that many solar systems might go through
earlier on in its lifetime, but not necessarily recently formed.
Is that correct?
Schuyler Wolff: Right.
So you have your star collapsing from your cloud, and then you have a proto-planetary
disc that's very gas-rich and over time planets form and the gas dissipates and
you're left with a debris disk phase, and that will likely last through the end
of the star's lifetime, though it might
change a bit as the planetesimals collisionally grind into
smaller and smaller pieces.
Christian Ready: So the debris disc can linger after the planets, the
main planets at least have formed?
Schuyler Wolff: Right, exactly.
Our own Kuiper belt and asteroid belts are sort of the, our debris discs.
George Riecke: Might be useful to put some timescales on this.
It's true that planets form out of disks of gas and dust around young stars.
But those discs dissipate in five or 10 million years, and so a a
star as old as Fomalhaut, which is about 500 million years old, you
don't expect any of that to be left.
So this, this is dust that has to form from a totally different process.
And as Skylar said, this is from collisions between small bodies in the
system and they pulverize each other and the results of the pulverization
that are dust, the dust then drifts out into Circumstellar space.
The star warms it up and then we see it in the infrared.
And it could be very hard to detect in other ways.
Christian Ready: Okay, and then after this inner disk, we have a gap, and
then we have the intermediate belt.
Now, do you think that this would be something akin to the asteroid belt?
András Gáspár: Well, it's at a colder region, right?
This is almost at a 80 astronomical units for Fomalhaut, so it's not an
analog, per se, to the asteroid belt.
What's really neat about it is though, is that we have this inner
gap, which separates that inner disc and this intermediate belt.
Which is most likely formed due to planet being in there and sculpting that gap.
So we have an indirect evidence of a possibly of a planetary object
orbiting around Fomalhaut there.
Christian Ready: When I first saw this image, it reminded me of those beautiful
ring structures surrounding forming planetary systems that were taken by the
ALMA array of radio telescopes in Chile.
I realize ALMA's operating on a much longer wavelength, but any idea as
to why it looks so narrow in ALMA?
Schuyler Wolff: Yes.
So I guess there's two ways to answer that question.
First, what is the difference between James Webb and ALMA?
And the main difference is when you're looking at a dust disc like this, the
wavelength you're using to investigate the disc coincides roughly with the size of
the dust grains that you're looking at.
So ALMA sees mostly millimeter-sized dust, which is less sensitive to things
like radiation pressure that drives these smaller dust grains outward.
Whereas James Webb we're looking at things that are tens of microns
in size, which are a little more sensitive to things like this.
But we also know from dynamical modeling that this ring seen with ALMA is too
narrow to be unperturbed by planets.
So there's a planet likely that is causing this ring to be as narrow as it is.
Christian Ready: Okay, so there's at least one planet there and it's
sculpting the ring a little bit.
And speaking of planets, I know that there was some talk many years
ago about, "hey, we found a planet around Fomalhaut, uh, Fomalhaut b,"
and now I see reading in the paper.
It's referred to as the, uh, the Great Cloud of Fomalhaut.
So what happened to Fomalhaut's planet?
András Gáspár: So just seeing the Fomalhaut b object with HST, uh, in
2008, that was a spectacular observation.
If you think about it.
We saw something moving in scattered light observations with HST, so
that was a spectacular observation.
Unfortunately, follow-up observations with HST seemed to show that object
both fading, slightly, getting extended.
And on an orbit that seemed to show it leaving the system, so
not really on an elliptical orbit.
All of these observations hinted at Fomalhaut b possibly being a result
of a massive collision producing a lot of small dust, which is why it
was even visible in scattered light.
Planets don't tend to be really visible and scattered light.
This great dust cloud that you mentioned is a seemingly a big
clump of dust that's located within this outer Kuiper belt analog ring.
We don't know specifically what its nature is at this point.
It could well be a background object, but it coinciding exactly with the ring is
lower probability, so it's very likely a big cloud of dust also possibly produced
by a large scale collision in that belt.
Christian Ready: That rolls right into my next question.
Where are the planets?
How come we aren't seeing planets in MIRI?
And is that a surprise?
George Rieke: So planets are really faint.
In fact, planets that are less massive than say Saturn are below
the detection limits, even for JWST.
So you can move the dust around with planets like Neptune and Uranus,
and they're the most common form of large planet around other systems.
So there could be lots of planets in there whose presence is only made apparent by
their rings and patterns like we see with Fomalhaut, and that we can't detect in
any other way yet until we've developed something even more powerful than JWST.
Christian Ready: In your paper you had deprojected Fomalhaut.
So obviously it's not truly an elliptical ring as we see it.
This is a function of projection on the sky.
How did you manage to create these deprojected images to
make them look more face-on?
András Gáspár: Well, first of all, let's just say that this figure
shows that we took images not only at 25 microns, but also at 15
and-a-half and 23-microns as well.
The 15 and-a-half micron image and the 23-micron were taken through
chronographs, and the 15 and-a-half one is taken through what we call the
Four-Quadrant Phase Mask chronograph,
which allows us to go to much smaller inner working angles.
So we see the much hotter and closer-in dust at 15 and-a-half microns, and you
can still see that there's contribution from the inner disk at that wavelength.
The 23-micron chronograph has a very large blocking area, so that's not saturation,
that is the chronograph, literally blocking out the
internal parts of the disc.
To answer your question, I fitted the disc contours with orbital
paths around Fomalhaut and just used those values to deject the images.
There's nothing particularly difficult about that part, but it does give
you an idea of how the system would look like if you'd viewed from above.
And since George commissioned this one, maybe he should talk about it.
George Rieke: Well, all I did was insist it be done, Adam Block, who is
a very skilled person with manipulating astronomical data to make spectacular
but scientifically correct images.
And so Adam did the heavy lifting on this, but it shows how the
whole system is assembled.
So you could see why the JWST image is so unique.
If you go to what I call the "assembly diagram", that kind of makes it
clear which telescope did what.
Christian Ready: That is spectacular.
Wow.
Might Fomalhaut eventually come to the point where it does start to settle
down, have its planetary system, raise a family of planets, and,
and get all that dust out of there?
Do you think that's a likely outcome?
András Gáspár: Well Fomalhaut is an early-type star, right?
So it doesn't have a too long of a lifetime.
It's about halfway through or even further of its life.
It's around four, 500 million years old.
A stars live up to, what, 800 million years?
So it doesn't have that much more to go.
Christian Ready: Thank you all so much.
This is just exciting results and congratulations and can't
wait to see what you find out with Epsilon, Eridani and Vega.
Guests: Thank you.
Thank you much for having us let you know.
Christian Ready:All right.
Okay.
Uh, I don't know what's going on here.
I can't seem to find the pause on my recording, but I'm, I'm
assuming it, it is recording.
Good grief.
My, my pause control, it says record, it says we're recording.
Wow.
George Rieke: This is the blackmail tape, right?
Christian Ready: Yeah, it's supposed to be, yeah.
Except, you know, it's kind of hard to, uh, it's kind of hard to, uh, have
a blackmail tape when you, you know, can't seem to learn how to run it.