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Last week, humanity’s most advanced space telescope, the James Webb
Space Telescope, released its first official batch of photos to the public.
And I’m not gonna lie, they were very good.
But these aren’t technically the first images the telescope captured.
During its post-launch commissioning program,
astronomers captured a bunch more while testing the cameras,
to make sure JWST could deliver on its promise to “unfold the universe”.
And last week, in a document published jointly by NASA and the European
and Canadian Space Agencies, they detailed exactly how great
this space-based observatory is going to be at doing just that.
Reality doesn’t always meet our expectations, so after the telescope settled
into its fancy orbit around the Sun 1.5 million kilometers from Earth,
astronomers spent 6 months actually testing the equipment
to see what they might need to account for when crunching their data.
And that involved capturing a bunch of test images for a bunch of different reasons.
Like, for example, have you ever stared at a light source for too long, and then
you look away, and your eyes still see the ghost of what you’d been looking at?
Well, that can also happen with telescope detectors.
So one of the tests astronomers needed to run was how this new-fangled
telescope handled staring at bright sources and how long those ghosts,
called latent images, would stick around in later observations.
The target of this test was a special kind of galaxy, known as a type II Seyfert.
Seyfert galaxies, like their brighter quasar cousins, are powered
by supermassive black holes in their centers, actively gobbling up matter
and throwing out light all across the electromagnetic spectrum.
In other words, there’s a really bright point of light in the middle
that JWST is going to have to stare at for a bit.
Which it’ll want to do, because these objects can help astronomers
understand how galaxies evolve over their lives
The image on the right here, belonging to the galaxy NGC 6552,
took about 30 minutes for JWST to capture.
The image on the left was taken by Hubble at a slightly different wavelength,
but just like that amazing deep field image everyone went gaga over last week,
the JWST image reveals some galaxies that Hubble did not.
Based on the data, it looks like JWST’s detector can get back to normal
after 15 to 30 minutes, depending on how long it was looking at a source.
That’s a pretty respectable downtime when you’re trying to study light
that took hundreds of millions of years to get to us.
Another test astronomers had to run was whether this telescope
could help itself remove those latent images.
For that, it turned to one of the most recognizable planetary nebulas out there:
the Cat’s Eye Nebula.
Now, despite their name, planetary nebulas are the death wails of stars
too small to go supernova.
As the core contracts into a dense remnant called a white dwarf,
the outer layers of gas are sloughed off into interstellar space,
where they can interact with local dust to make some really beautiful shapes.
After checking out this gorgeous glob of gas and dust,
astronomers put the telescope through a process called annealing,
which uses temperature changes to reset its detectors back to their baseline.
The chillest detector on board, called MIRI,
was warmed by a small heater system until it was about 20 Kelvin,
before cooling back down to 7 Kelvin.
That’s 7 Kelvin above absolute zero.
And the tests did confirm that these anneals improved the image latency.
With such a reset, JWST can get back to work, faster.
And finally, JWST needed to prove how well it could capture
clean images of objects that move.
I mean, all objects in space move relative to each other,
but we’re talking about things that are way, way closer
to Earth than planetary nebulas, let alone separate galaxies.
And that makes them appear to move way faster in the sky.
Just think of the roadsign flying past, versus the mountain in the background.
So the telescope targeted a collection of asteroids, as well as
one of the most dynamic-looking planets in our solar system: Jupiter.
In this image, you can see Jupiter’s icy moon Europa on the left.
And the circle in its center is just there to block out some of the light.
But you can also see the shadow Europa is casting on Jupiter.
Because this telescope looks at infrared light,
that corresponds to that shadowy spot being cooler!
But you know what’s even cooler than that?
In other images, you can see Jupiter’s very faint rings!
By capturing such speedsters, astronomers demonstrated that JWST
can study fast-moving objects.
Up to twice as fast as they expected they were going to be able to, in fact.
That opens up even more opportunities for the telescope
to help us understand our own solar system, not just others.
And that is not the only good news.
This commissioning period demonstrated that JWST is performing better overall
than ground tests suggested it would.
With cleaner mirrors than expected, the blacks are darker,
and with better aligned optics, the images are sharper, too.
So it’ll be even easier than anticipated for the telescope to peer back in time
over 13.5 billion years, to when the very first galaxies were forming.
So congratulations to the JWST teams all around the globe,
and to all the astronomers who get to dive into that juicy data
hiding in these galactic glamor shots.
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