Eclipse – 1 year, JWST spies the warmth of the supernova Cas A

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On November 14, 2022, I was privileged indeed to give a talk for the Central Arkansas Library System (sponsored by the very good folks at the Arkansas Space Grant Consortium) about the upcoming total solar eclipse across the US on April 8, 2024 — just 364 days from now (remember, 2024 is a leap year).

Unfortunately an icy rain kept some of the audience home, but the talk was recorded and is online so you can watch from the comfort of your own home.

This was a fun talk to give — my first eclipse public lecture since I finally, finally saw one for myself — and I’ll note I’m happy to travel to places to give it. Museums, schools, universities, libraries, what-have-you. The talk is different every time, so watching the video will give you a flavor for it but I can adjust it to your locale or whatever you need. I have talks on tons of other topics, too: exoplanets, JWST, telescopes and observing in general, the intersection of art and science, asteroid impacts and what we can do about them, and more.

Interested? Contact my agent Beth Quittman with Samara Lectures. She’ll be happy to talk to you!

Pic o’ the Letter

A cool or lovely or mind-bending astronomical image/video with a description so you can grok it

I have a soft spot in my heart (and possibly my head) for Cas A.

It’s a supernova remnant, the expanding debris from the catastrophic explosion of a massive star at the end of its life. I am fascinated by supernovae, and some years ago when I was at Sonoma State University I worked on doing the education and public outreach for several NASA astronomy missions, all of which studied these events in one way or another.

Cas A was the topic of one lesson I developed, a piece of software that allowed a student to figure out what chemical elements are in the debris. The calcium, iron, sulfur and more created in the titanic explosion give off X-rays, and the lesson used real data from the XMM-Newton observatory to observe them.

But supernova remnants give off more than just X-rays; they emit across the electromagnetic spectrum, and that includes infrared light, the kind that JWST sees.

And sees very well. Behold, Cas A:

WHOAAAAAA.

Cas A (short for Cassiopeia A) is about 11,000 light-years from Earth, and the light from the explosion first reached us in the mid-1600s. It appears as a circular shell on the sky, though it’s really a thin-shelled bubble. When we look toward the edge we see through more glowing material, so it’s brighter there. That also means that most of the material that appears to be inside the bubble is actually likely on the near or far edge of the shell, and not really filling it.

JWST’s infrared vision is sensitive to warm cosmic dust, and that makes up a lot of what we see here. I don’t have a lot of details because this image was issued as a press release, and not a journal paper (hopefully one will come out soon). However, the release notes that the orange arc at the top is probably where material screaming outward from the explosion has slammed into interstellar dust — grains of silica and soot (well, complex chains of carbon atoms) — and warmed it up.

The green filaments along the bottom are interesting. What appears as green in this image is actually light at a wavelength of 11.3 microns — light with wavelengths 15 times longer than the reddest red you can see. The aforementioned soot can glow at these wavelengths, so that’s likely what we’re seeing here, and it’s a little odd that it’s only seen in one spot like this instead of all over the nebula. The press release doesn’t go into details because apparently it’s not clear what’s going on there, even to the astronomers who took this image. I guess we really do have to wait for a paper to be published to understand it all.

The smaller pinkish circle is probably material from the exploded star itself; all the newly forged elements created in the immense heat and pressure of the explosion that fused lighter elements into heavier ones. I love all the knots and filaments in it; the structure looks graceful and delicate, belying the fact that the explosion launched octillions of tons of billion-degree plasma into space at a decent fraction of the speed of light.

See: How can you not love supernovae?

The expansion of that material into space appears slow to us here on Earth due to the incredible distance to the remnant — over 100 quadrillion kilometers. But our eyes on and in space are keen. The Chandra X-ray Observatory has looked at Cas A over so many years that the material’s motion can actually be directly seen. Watch this:

Yegads. The gold colored stuff is from a static, unmoving Hubble image that helps you see the filaments and knots seen by Chandra (colored blue and purple) moving out from the center. The green arrows point out “reverse shocks” where material expanding outward slams into slower moving stuff in space, generating a shock wave that appears to travel back through the debris toward the explosion’s center.

Cas A is a fascinating object. It’s located in the thick of the Milky Way, which absorbs most of the visible light (the kind we see) so it’s actually very faint. However, X-rays and infrared light can pierce through the interstellar junk floating out there, giving us a more clear picture. And in this case, an exceptionally clear and sharp one.

Supernovae make a lot of dust in he explosion, so I’m excited to see what else JWST has to show us. There are a lot of these magnificent objects in the sky, so I expect we’ll see lots of amazing images. Stay Tuned.

Et alia

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