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The James Webb Space Telescope has been in space for over a year now.
The images it takes of the universe continue to captivate, with their high resolution detail
and breath-taking beauty.
However, although it may sound counterintuitive, it is often what the Webb does not see that
allows it to really shine a light on the universe’s inner workings.
This seeing-without-seeing might sound strange, but it’s a foundation on which much modern
observation of the universe is based.
Through clever techniques, it allows us to understand the chemical composition of molecular
clouds and nebulae, the make-up of atmospheres around exoplanets, and the existence of rings
around asteroids in our own solar system.
The JWST is uniquely placed to take advantage of these clever techniques, due to its unprecedented
sensitivity and precision.
I’m Alex McColgan and you’re watching Astrum.
In this second video on the spectacular sights captured by the James Webb, I will show you
the awesome power of not seeing, as well as seeing, in helping us expand our understanding
of space around us.
Let’s begin with this image of NGC 346; a cluster of stars and associated nebula found
in the Small Magellanic Cloud, 210,000 light years away from us.
NGC 346 is interesting to scientists because the conditions and amount of metals found
in this area are similar to conditions back 2 billion years after the Big Bang, in a highly
energetic period of the Universe’s history known as the cosmic noon.
Countless stars and galaxies were rapidly forming during this point in time.
By studying this nearby modern contemporary, scientists can get a better idea of what cosmic
noon might have been like.
But how do scientists know the metallic composition of these beautiful swirls of stellar matter?
One method is through looking at emission lines.
When gases get hot, say because they have been warmed up by a star, the atoms that make
them up seek to dissipate that heat by emitting radiation.
However, for reasons that have something to do with quantum mechanics (which we won’t
dive into here), every atom can only emit radiation at a specific, unique wavelength.
This gives elements distinct chemical fingerprints – if you know the wavelengths of light given
off by oxygen, you can always tell when super-heated oxygen is the source of any light you come
across.
So, by seeing this light, the JWST has an idea of the chemical composition of this nebula.
The JWST is particularly suited to investigating nebula like these, as infra-red is much more
able to pierce dust clouds and see what lies at their heart.
Webb’s superior sensitivity allowed it to detect details that had never been seen here
before, including the small disks of dust that were forming around developing protostars,
potentially even marking the beginnings of planets.
However, these are standard methods of observation.
I started this video by talking about seeing through not seeing.
And when it comes to astronomy, merely looking at the light emitted by objects is often not
enough.
For instance, recently the JWST imaged this: This is an ice cloud.
More specifically, it is the Chamaeleon I dark molecular cloud, another birth-place
of stars.
As you can imagine, an ice cloud is not hot enough to radiate light with emission lines.
So here scientists need to use a different technique to learn its chemical composition.
But thanks to Webb’s piercing vision, a different method can be employed.
As I said earlier, when atoms become excited, they release radiation.
But this process works in reverse too.
When cold atoms are hit by radiation, they can become excited.
They absorb the energy, becoming a little warmer.
This has a clever implication.
It means that if you shine a continuous spectrum of light through a gas cloud, and see which
frequencies of light get blocked by that cloud, it’ll tell you just as certainly what elements
make up that cloud as if you’d heated them up and they were radiating.
This is what I mean by seeing through not seeing.
Of course, it does hinge on light shining through the cloud you want to look at.
This occurs through all the stars sending out light from behind the Chamaeleon I dark
cloud.
The light given off by stars is much more varied in its wavelength than the light given
off by specific gases, as solid objects give off photons under different rules to gas.
This provides a smooth, continuous light source to check absorption lines against.
There is a problem, though.
For objects as large as a molecular cloud, they can be too dense for starlight to be
able to penetrate it.
This is where the power of the JWST comes into play.
Thanks to the JWST’s unprecedented sensitivity, for the first time scientists have been able
to detect the light from distant stars through the thick cloud of Chamaeleon I, allowing
them to see its chemical composition.
What they found was a surprise – not only does the Chamaeleon I dark cloud contain water
ice, but also some of the fundamental building blocks of life; ammonia, methane and methanol.
This means that stars and planets that one day form in this icy cloud will start off
with some quite complex chemicals to get the ball rolling.
And if this turns out to be common, it makes it much more likely that worlds capable of
bearing life are actually widespread throughout the universe, decreasing the likelihood that
we are alone in it.
Spectroscopy – the science of studying the chemical makeup of objects from their absorption
lines – is a very versatile tool.
And it extends to much more than molecular clouds or nebulae.
Through it, we can also learn much about the atmospheres of exoplanets.
Webb was able to discover the chemical makeup of one such exoplanet – WASP 39b, a Jupiter-sized
exoplanet 700 light years away from us – by waiting until it passed in front of its own
star.
Light from the star filtered through the planet’s atmosphere, where the gases within absorbed
the light at certain frequencies, leaving their distinct fingerprints on what remained.
Webb detected Sulphur dioxide in WASP 39b’s atmosphere – the first time this compound
had ever been seen in an atmosphere outside of our solar system.
Webb also provided a complete breakdown of all other chemicals and elements present,
including some water vapour.
Spectroscopy, as impressive as it is, isn’t even the only way the JWST makes discoveries
by not seeing.
There is a second process, known as occultation, that astronomers have been making use of over
the last century.
Rather than searching for the spectroscopic breakdown of the light from stars, watching
for occultation involves noting a star’s brightness over time.
By looking out for the sudden dimming of stars, scientists can discern the presence and characteristics
of dark objects that pass in front of them.
And the JWST is very good at spotting such dimming moments.
In our solar system, between Saturn and Uranus, there lies a rather unusual asteroid called
10199 Chariklo.
It is 250km in diameter, and is the largest of the asteroids known as the centaurs; asteroids
that tend to orbit between Jupiter and Neptune.
However, that is not its claim to fame.
Chariklo is impressive because in 2013 it was discovered to be one of 5 objects in our
Solar System to have rings.
For a while, scientists did not think that objects as small as Chariklo could support
rings.
Even now, they are unsure whether these rings are only here because they are relatively
new – forming in the last few million years or so – or whether some gravitational phenomenon
caused something like shepherd moons, keeping them in place.
The JWST tested its ability to observe occultation by trying to spot these rings as Chariklo
passed in front of a distant star.
This was not as easy to do as it sounds.
It takes extremely precise predictions to know where Chariklo would orbit, to know which
star to watch.
Given the size of objects in space, even the smallest miscalculation would result in no
occultation being observed.
That said, Webb was able to spot Chariklo and its two rings as they passed in front
of the star, noting the occultation of the asteroid itself as well as each of the rings,
as seen in this video.
The rings were too small to be imaged by JWST directly, but from the sudden dimming in the
star’s brightness Webb was able to clearly make out the rings, which are thought to orbit
about 400km from Chariklo itself.
The larger of the rings is only 6.9km wide, and the smaller one is a tiny 0.12 km.
It is not yet clear what these rings are made of, but Webb was able to detect crystalline
water ice on the main body of Chariklo.
With further observations, more information about these rings will come to light.
And speaking of rings, there is one more image I want to show you.
This is just one that I found spectacular – the strange rings of Wolf-Rayet 140.
These reddish-purple rings are like nothing I’ve ever seen in space before.
The astronomers who first saw it thought that something might be wrong with their equipment.
The rings seem more like the ripples of a pool, or the rings of a tree, than actual
interstellar objects.
And yet these rings actually represent over a hundred years of a truly incredible phenomenon.
At the heart of these rings lies a binary star system.
Every 8 years, the two stars at the centre of this system orbit close to each other,
and their stellar winds interact in such a way as to blow a fresh ring of dust outward
into space.
There are at least 17 rings, meaning this process has been ticking along once every
8 years for the last 130 years or so.
This phenomenon is large – the furthest ring is 70,000 times the distance from the
Earth to the Sun.
The detail Webb was able to capture is incredible.
Previous glimpses at this system indicated that there might have been one ring, but it’s
incredibly blurry compared to the resolution captured by Webb.
These rings were useful for astronomers, as they provided opportunity to spatially document
the chemical compositions of the rings of Wolf-Rayet 140 over time.
Through these probes, scientists found what they believe to be Polycyclic Aromatic Hydrocarbons
(PAHs).
PAHs had been known for a long time.
They help in the formation of stars and planets, but their origin has long been a mystery.
Now, thanks to this discovery by the JWST, Wolf-Rayet binary stars have stepped forward
as one possible source for this crucial compound.
And it was only possible because of spectroscopy, and JWST’s ability to see and not see light
in incredible detail.
There will no doubt be many more discoveries the Webb will make in the years to come.
Such a powerful telescope can capture images at far greater clarity than the space telescopes
before it.
But I thought it was important to emphasise that not all the Webb’s discoveries are
stunning images in the night sky.
Many of its biggest breakthrough lie in the tiny hidden details of things not seen – light
not appearing when it might be expected to, indicating the presence of hidden chemicals
or celestial objects.
Because it turns out, it’s not always about what you see.
Sometimes what you don’t see is most informative.
Since I started Astrum a decade ago, this channel about space has grown in no small
part to you, the people who watch my content.
In the comments I’ve sensed your enthusiasm, and want to foster the incredible Astrum community
that’s grown over the years.
So, I’m making some improvements and upgrades to my Patreon and membership tiers.
I’m creating a discord server, where all levels of patrons will be able to come together
and share cool things they’ve learned about space, as well as interact with me and my
team.
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Thanks for watching!
If you want to have a look at more James Webb images, check out this playlist here.
And a big thanks to my existing Patrons and members for your support.
All the best, and see you next time.