Supernova Remnant Cassiopeia A: Cool Images of Hot Gas

Detail. JWST (NASA, ESA, CSA, STScI, D. Milisavljevic (Purdue University), T. Temim (Princeton University), I. De Looze (University of Gent))'s NIRCam image: Cassiopeia A (Cas A) in in near-infrared light. Red, green, and blue were assigned to 4.4, 3.56, and 1.62 microns. (image released December 10, 2023)
Part of Cassiopeia A, image from James Webb Space Telescope’s NIRCam. (December 10, 2023)

That’s more than just a pretty picture. Well, part of a pretty picture.

It’s our latest look at the Cassiopeia A supernova remnant. Webb’s high-resolution cameras are showing details that scientists have never seen before.

James Webb Telescope Captures Image of Supernova That ‘Absolutely Shattered’ a Star
Will Sullivan, Smithsonian Magazine (December 13, 2023)

“…In April of this year, Webb imaged the stellar remains in mid-infrared light. Now, the newly released snapshot shows Cas A’s colorful, orb-like wisps captured using Webb’s Near-Infrared Camera (NIRCam).

“‘With NIRCam’s resolution, we can now see how the dying star absolutely shattered when it exploded, leaving filaments akin to tiny shards of glass behind,’ Danny Milisavljevic, an astronomer at Purdue University who led the research, says in a statement from NASA. ‘It’s really unbelievable after all these years studying Cas A to now resolve those details, which are providing us with transformational insight into how this star exploded.’…”
[emphasis mine]

NASA’s Webb Stuns With New High-Definition Look at Exploded Star
Hannah Braun, Christine Pulliam, Danny Milisavljevic (Purdue University), Ilse De Looze (UGent), Tea Temim (Princeton University); Webb Space Telescope (December 10, 2023)

“…Webb’s NIRCam (Near-Infrared Camera) view of Cas A displays this stellar explosion at a resolution previously unreachable at these wavelengths. This high-resolution look unveils intricate details of the expanding shell of material slamming into the gas shed by the star before it exploded….”

That’s what I started talking about this week.

But the Cassiopeia A supernova’s underwhelming appearance, or maybe non-appearance, reminded me of famines, coffeehouses, and other malign menaces.

So here’s what I had, Friday afternoon:

Spotting an Invisible Supernova, Coffeehouses, — [disconnecting]

JWST (NASA, ESA, CSA, STScI, D. Milisavljevic (Purdue University), T. Temim (Princeton University), I. De Looze (University of Gent))'s NIRCam image: Cassiopeia A (Cas A) in in near-infrared light. Red, green, and blue were assigned to 4.4, 3.56, and 1.62 microns. (image released December 10, 2023)
Cassiopeia A: a near-infrared image from James Webb Space Telescope’s NIRCam. (December 10, 2023)

Around the time folks living in lands between the Mediterranean, Caspian, and the Persian Gulf, were turning wild critters into domestic sheep, a massive star exploded.

Light from the explosion should have reached Earth in the 1690s. Maybe it did. But if so, nobody noticed. Nobody wrote about a new star, at any rate.

Folks near the Baltic Sea, in France, and in Scotland, might have been preoccupied with famines; but there’s nothing on record elsewhere, either. Odd, that. Not the famines. Nobody noticing.

Maybe it was the prevalence of coffeehouses.

Fred Barnard's 'Discussing the War in a Paris Cafe,' Illustrated London News. (September 17, 1870) via Wikipedia, used w/o permission.A few generations earlier, when the Dutch East India Company opened for business, coffeehouses in Mecca were giving serious-minded folks there fits.

Seems that there were entirely too many ideas being discussed.

I haven’t, by the way, seen the Dutch East India Company blamed for either coffee or coffeehouses.

Anyway, coffeehouses caught on in Europe. Serious-minded folks there were, arguably, just as alarmed as their counterparts back in Mecca had been.1

“…In 1675 King Charles II made an attempt to shut down coffeehouses with an edict. King Charles II stated that coffeehouses ‘have produced very evil and dangerous effects,’ and were also a ‘disturbance of the peace and quiet realm,’….

“….The Licensing of coffeehouses was not just to procure revenue for the crown, but also to regulate social discipline within the communities that the houses served. London’s elite viewed all public houses as having the potential for public nuisance, and needed close attention and control. Not only did keepers have to demonstrate that they paid duties on the goods they sold, but they also had to demonstrate that they were loyal subjects….”
(“The Coffeehouse Culture“; Erin Burg, Sarah Brady, Maddie Thomas, Peter Schottenfeld, Lili Bishop, Hilary Lamb; British Literature Wiki; University of Delaware)

[reconnecting] — Flamsteed’s Star, and Another Supernova

Tycho Brahe's De nova stella title page, a facsimile reprint (1901)of the original edition (1573).Or maybe someone did see the Cassiopeia A supernova (Cas A), after all.

Nobody’s been able to spot John Flamsteed’s just-barely-visible-star, 3 Cassiopeiae, since he recorded its position in August of 1680.

It would be pretty close to where Cassiopeia A is, so maybe someone did record the supernova, after all.

Unlike Flamsteed’s dim and disappearing 3 Cassiopeiae, Tycho’s Supernova (1572-1574) got the attention of a whole mess of folks, including the Wanli Emperor’s administration; and that’s another topic.

These days, the star that flared and died in our skies from November 1572 to early 1574 has a standardized designation: SN 1572. But “Tycho’s Supernova” is still in play as a tip of the hat to Tycho Brahe’s massive analysis of the phenomenon: “De nova et nullius aevi memoria prius visa stella”.

If Cassiopeia A had been as bright as Tycho’s Supernova — but it wasn’t.

Flamsteed’s 3 Cassiopeiae was, at its brightest, barely visible. Tycho’s Supernova got as bright as, or brighter than, Venus at its brightest.

No matter whose report was more accurate, SN 1572 was bright.

Interestingly, Tycho’s Supernova was in Cassiopeia, too: and roughly the same distance from Earth.2

So how come one supernova was a shining beacon in Earth’s sky for years, while the other was — at best — a transient flicker?

That’s a good question.

I’d talk about how and why two whacking great explosions, going off practically next to each other and at nearly the same time — on a cosmic scale — produced a spectacular new star in one case: and a barely-noticeable blip in the other.

But I can’t.

Mainly because scientists haven’t figure that puzzle out. Not yet.

Four Ways Stars Explode: a NASA/JPL (very) Short Video

I can, however, and will, skip lightly over what we’ve learned since Tycho’s Supernova lit up Earth’s sky.

For starters, that was the first well-documented sky phenomenon which had obviously and spectacularly changed on time scale that humans notice easily.

Before that, stuff we see in the sky, other than the sun, moon, planets, comets and clouds, seemed to never change. And don’t, not appreciably, not over the span of a human lifetime.

Aristotle figured comets — and meteors, forgot about them — were a sort of atmospheric thing, like clouds, and I am not going to dive down that rabbit hole.

Again, Tycho’s Supernova showed that stars can and do change. At the time, that was an important new idea. Which is another rabbit hole I’ll ignore this week.

Basically, folks had been noticing and jotting down notes about new stars for millennia.

I figure Tycho’s Supernova happened at the right time, when natural philosophers were realizing that Aristotle’s cosmology wasn’t the best fit with observations.

Anyway, 19th century telescopes let astronomers get more exact data. Since then, we’ve worked out how stars convert mass into energy: which let scientists develop mathematical models that show how some stars explode.

I’d planned in geeking out over electron degeneracy pressure — electrons can be degenerate, who knew? — core collapse scenarios, stellar evolution, and exploding stars.

But you’re in luck. I’ve been a bit distracted this week, and that’s not going to happen.

Instead, I looked up a pretty good — and short, one minute 37 seconds — video put out by NASA and JPL. It’s the one embedded a few paragraphs back.3

We don’t know for sure what process produced the Cassiopeia A supernova remnant.

Cassiopeia A: Might have been a FELT

NASA, ESA, A. Feild (STScI)'s illustration: 'Model for the Creation of a Fast-Evolving Luminous Transient' - A proposed model for a Fast-Evolving Luminous Transient (FELT). Left panel: an aging red giant star loses mass via a stellar wind, ballooning into a huge gaseous shell around the star. Center panel: the massive star's core implodes, triggering a supernova explosion. Right panel: the supernova shockwave hits the outer shell, converting the kinetic energy from the explosion into a brilliant burst of light. The flash of radiation lasts for only a few days: one-tenth the duration of a typical supernova explosion.
A. Feild’s “Scenario for a Fast-Evolving Luminous Transient” (FELT). (2018) via NASA, ESA

But it’s likely, or at least possible, that the Cassiopeia A supernova was what we call a FELT: a Fast-Evolving Luminous Transient.

If that’s so, it would have been a very massive red giant that ‘burped’ before exploding.

A little before its core collapsed, it would have blown off a fair amount of stuff: like our star’s solar wind, only on a Brobdingnagian scale.

Then, when its core collapsed — triggering a series of fusion reactions that produce elements we’re made of — there’d be this shell of cooler gas and dust between the exploding star and the rest of the universe.

When light — and a little later, leftover star-stuff — hit that shell, the stellar burb-bubble would light up. Briefly. But it wouldn’t produce the cosmic beacon that we’ve come to expect from supernovae.4

Transposing the Invisible: Infrared Astronomy

NASA, ESA, CSA, STScI, Danny Milisavljevic (Purdue University), Ilse De Looze (UGent), Tea Temim (Princeton University)'s images: supernova remnant Cassiopeia A (Cas A) as captured by NASA's James Webb Space Telescope's (left) NIRCam (Near-Infrared Camera) and (right) MIRI (Mid-Infrared Instrument). (December 10, 2023)
Cassiopeia A images from NIRCAM, MIRI. (2023)

It’s not just different colors that make those two images different. The James Webb Space Telescope’s NIRCam and MIRI show us that Cassiopeia A’s light is brighter in different places, depending on what “colors” of infrared light we pick.

Black body radiation curve, Astronomy Education at the University of Nebraska-Lincoln.My hat’s off to NASA, ESA, and all the Webb Telescope folks; for discussing why different images taken of things like Cassiopeia A look — well, look different.

Infrared Astronomy
NASA, A. Feild [STScI]; Webb Space Telescope

“…Infrared light is important to astronomy in three major ways.

“First, some objects are just better observed in infrared wavelengths. Some bodies of matter that are cool and do not emit much energy or visible brightness, like people or a young planet, still radiate in the infrared. Humans perceive this as heat, while some other animals, like snakes, are able to ‘see’ infrared energy.

Visible light’s short, tight wavelengths are prone to bouncing off dust particles, making it hard for visible light to escape from a dense nebula or protoplanetary cloud of gas and dust. The longer wavelengths of infrared light slip past dust more easily, and therefore instruments that detect infrared light—like those on Webb—are able to see the objects that emitted that light inside a dusty cloud. Low-energy brown dwarfs and young protostars forming in the midst of a nebula are among the difficult-to-observe cosmic objects that Webb can study. In this way, Webb will reveal a ‘hidden’ universe of star and planet formation that is literally not visible….”
[emphasis mine]

There’s more, but I’m running late. So I’ll put some links in the footnotes, and plan on talking about infrared astronomy another time.5

Cosmic Scale and a 15-inch Telescope

Charles Betts, Adam Block, NOAO, AURA, NSF's image: Cassiopeia A supernova remnant
Cassiopeia A, seen in visible light. Charles Betts, Adam Block, NOAO, AURA, NSF.

Stellarium's sky chart, showing Cassiopeia A position (2018). Via Bob King, Sky and Telescope. (November 28, 2018)Someone with a good 15 inch telescope, very good sky conditions, and a degree of patience, can see Cassiopeia A.

It’s not nearly as spectacular as the latest Webb Space Telescope images: but observing it is the sort of thing amateur astronomers set as a goal.

And, once they’ve succeeded, write about. Some of them, anyway.

Seeking Cas A, the Ghostly Remains of a Mysterious Supernova
Bob King, Sky and Telescope (November 28, 2018)

“One night not long ago, I drove to dark sky with my 15-inch telescope to see if I could find the faint supernova remnant Cassiopeia A, or simply Cas A. I had always considered this remnant impossibly faint and off-limits for my scope, but read of others seeing it, so I put it on my list for a dark night when Cassiopeia arced high in the northern sky.

Located 11,000 light-years away within the Milky Way, the remnant formed in the aftermath of a Type IIb supernova, when a red supergiant with some 16 times the mass of the Sun reached the end of its life. After shedding its hydrogen envelope, the star’s core collapsed and then rebounded, sending a shock wave through its outer layers that resulted in a massive explosion, blowing it to bits.

“In its wake, a knotted arc of former star-stuff has been expanding outward from the explosion site ever since. Based on the speed of the ejecta, astronomers estimate the event occurred about 330 years ago, making Cas A one of the youngest supernovae known in the Milky Way….”
[emphasis mine]

I recommend Bob King’s article, which includes a sketch he made of Cas A.

However, “the event” did not occur about 330 years ago. That explosion was 11,000 light-years away, so what happened around 330 years back was light from the blast washing past the Solar System.

I’m not faulting Bob King for saying it “occurred about 330 years ago”. He’s following an convention I’ve noticed in astronomy articles. The time of events like supernovae are placed at when their light reaches us.

It makes sense, since ‘time-observed’ is generally known and verifiable; while defining when an event actually occurred depends on our knowing how far away it was.

And we still don’t know distances — not exactly — for some fairly well-known objects, like the Spaghetti Nebula.6

“…To Follow Knowledge like a Sinking Star….”

Brian H. Gill's 'All Experience is an Arch'. (2016)

Alfred, Lord Tennyson (1833)

“…this gray spirit yearning in desire
To follow knowledge like a sinking star,
Beyond the utmost bound of human thought….

“…my purpose holds
To sail beyond the sunset, and the baths
of all the western stars, until I die….”

Shylaja B's Figure 3 - uploaded by Shylaja B - The chart for SN 1572; notice the proximity to β Cas. From 'HISTORICAL NOTES Records of supernovae from India'; Shylaja B; Current Science, Published by Current Science Association (April 2019) via ResearchGate.netSpeaking of distances: I mentioned that Tycho’s Supernova happened near (on a cosmic scale) the supernova that left us the Cassiopeia A remnant.

Cas A is roughly 11,000 light-years out, in the general direction of Beta Cassiopeiae. We’re pretty sure about that distance, although one news release listed its distance as 11,000 and 10,000 light-years.

I haven’t found a resource that gives details on uncertainty for Cas A’s distance, but there’s a good consensus that it’s 11,000 light-years out.

Tycho’s Supernova’s remnant is a bit closer: between 8,000 and 9,800 light-years away, also in the general direction of Beta Cassiopeiae. But a probe heading there would be tacking a bit toward Earth’s current north star, Polaris.

Odds are that we’ll send a probe to Beta Cassiopeiae before setting sights on either of those supernova remnants. Beta Cassiopeiae — Caph, a name confirmed by the IAU — would be worth checking out; although Altair, Denebola, and Vega, are much closer. And that’s yet another topic.

Point is that Caph is about 54 and a half light- years away. Tycho’s Supernova remnant and Cas A are something like 200 times farther away, and are fairly near each other. On a cosmic scale.

Which I think is cool. And may be scientifically significant, since that puts them in the Perseus Arm, the next spiral arm out from our neighborhood in the Orion Arm.7

“On to God!” — “Truth Cannot Contradict Truth”

NGC 4848 and other galaxies, image by Hubble/ESA.
NGC 4848 and other galaxies.

I was going to talk about why I don’t see a problem with paying attention to those parts of God’s creation we can see. Even if doing so means readjusting our assumptions about stars, starfish, or whatever.

But it’s late Friday afternoon. And, like I said, I’ve had a distracted week. What I was going to say, and a couple cartoons, will wait.

Basically, I figure that since science and religion both seek truth; honest research can’t interfere with an informed faith.

“…Religion and natural science are fighting a joint battle in an incessant, never relaxing crusade against scepticism and against dogmatism, against disbelief and against superstition, and the rallying cry in this crusade has always been, and always will be: ‘On to God!'”
(Religion and Natural Science, a lecture delivered in May, 1937, originally titled Religion und Naturwissenschaft. Complete translation into English: “Scientific Autobiography and Other Papers“, Max Planck (1968); via

“…Even if the difficulty is after all not cleared up and the discrepancy seems to remain, the contest must not be abandoned; truth cannot contradict truth….”
(“Providentissimus Deus,” Pope Leo XIII (November 18, 1893))

Now, the usual links:

1 Recent(ish) famines. Climate change, the early years (Pleistocene, Holocene, and agriculture’s start). Coffeehouses — also a supernova remnant:

2 A constellation, an ex-star, two astronomers, a politician and an empoeror:

3 Science and one of Aristotle’s books:

4 FELTs — or — giant burping stars:

5 Light, invisible and otherwise:

6 That’s right; the Spaghetti Nebula:

7 Stars and galaxies:

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About Brian H. Gill

I was born in 1951. I'm a husband, father and grandfather. One of the kids graduated from college in December, 2008, and is helping her husband run businesses and raise my granddaughter; another is a cartoonist and artist; #3 daughter is a writer; my son is developing a digital game with #3 and #1 daughters. I'm also a writer and artist.
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