Watch a Hubble Space Telescope video of a shock wave moving through gas of an exploded star

October 16, 2023   Issue #630

Subscribers are supernovae in the dark 

Astro Tidbit

A brief synopsis of some interesting astronomy/science news

In June 2023 — BAN Issue 579 — I wrote about the Cygnus Loop: how gas from a star that exploded 20,000 years ago is slamming into gas floating around in the galaxy, creating a lone, thin shock wave moving through the material. I showed a Hubble Space Telescope image of that part of the supernova gas from 2000 superposed on one taken in 2020 that together show the shock wave has moved through the gas.

The folks at Hubble just put out a press release about this, both with a link to the paper as well as a nifty animation of the two images, making the shock movement more obvious. Watch!

The animation repeats many times so you can see the movement more easily. Super cool.

While watching it, though, I noticed that several stars appear to move as the two frames blink back and forth. I think some of that is because the shapes of the stars in the images are a bit blobbier in the 2001 image (the earlier image was taken using WFPC2, a camera on Hubble that had slightly lower resolution than the WF3 which was used in the later image).

But if you watch individual stars closely you can see some move more than that accounts for. One, a fainter red star at the top of the image and a third of the way over from the left disappears completely between the observations!

I think some of those motions are real. Stars move through space, some at pretty high speeds, as they orbit the center of the galaxy, similar to how planets orbit the Sun. Most of the time those stars are really far away and the motion slow enough that you don’t see it, even with Hubble and a 20 year baseline. But in this case several do seem to move. This is called proper motion, and if you don’t account for it (properly, haha) you can get in trouble.

I surmise that the red star that disappears is a red dwarf. These are very intrinsically faint stars, so even Hubble can’t see them unless they’re relatively close to us. But if they’re closer that means their motion is easier to see — just like a car near you seems to zip past, while ones much farther away appear to move much more slowly. Perspective.

We call them the “fixed stars”, but they ain’t. If you wait long enough, and have keen enough eyesight, you watch the heavens move.

SciAm What SciAm

Stuff I’ve written for Scientific American

The Sun is getting feisty again, blasting off big magnetic storms that can head earthward and create havoc here on our homeworld… but also unearthly beauty, too. I wrote about aurorae (Latin plural for “aurora”) in my latest “Over Your Head” SciAm column, so please give it a read! You may need to log in to read it, but it’s free.

What’s Up?

Look up! There’s stuff to see in the sky!

Did anyone see the annular eclipse on Saturday? It was raining in Virginia, unfortunately, so I didn’t even get to see the ~30% partial eclipse. Boo. Tell me what you saw in the comments below, and if you have photos someplace please link to them, too, so I (and everyone else) can at least experience it vicariously. I’ve opened comments to everyone, free and paid subscribers.

Next up: The Big Show on April 8, 2024, when a lot of the US will see a total eclipse. I already have a series of public talks planned for that time, and I’ll put my schedule here once it’s finalized.

Shameless Self-Promotion

Where I’ll be doing things you can watch and listen to or read about

That reminds me: On October 19, at 7:00 p.m., I’ll be giving my “Under Alien Skies” talk at the Liberty Science Center in Jersey City, NJ, on their huge 29-meter planetarium dome (tickets are available here). I did a short interview about it with Jeremy Grossman, too. If you’re in the area Thursday come see!!

Et alia

You can email me at [email protected] (though replies can take a while), and all my social media outlets are gathered together at about.me. Also, if you don’t already, please subscribe to this newsletter! And feel free to tell a friend or nine, too. Thanks!