Hubble sees the expanding debris from an ancient catastrophe

June 19, 2023   Issue #579

Subscribers are shocking, and help me expand into the Universe 

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

One thing that still makes me awestruck is that we’ve been looking at deep space astronomical objects for so long with telescopes so precise that we can detect motion in these cosmic phenomena, seeing them physically move over time.

In real terms these motions can be huge, but the objects are so far away that this gets diminished by our distant perspective to an apparent verrrryyyyy slooooooowwwwww crawl. But, if you point something like Hubble a carefully chosen target you get images so sharp that this motion can be seen.

It helps, too, if the velocity at which it’s happening is something like 850,000 kilometers per hour!

In this case I’m talking about the Cygnus Loop, the expanding debris from a star that exploded roughly 20,000 years ago. It’s about 1,700 light-years from us, and so old that it now covers an incredible 3° of our sky — 6 times wider than the full Moon!

The gas from the star that went supernova all those millennia ago rushed away from the explosion site at thousands of kilometers per second, accelerated to such huge velocities by the mind-crushing energies of the event. As it did it pushed against the gas that already existed around the star, slowing until it was essentially coasting.

But it’s still expanding, and moving so fast that when it hits some cloud of material it slams into it and creates a shock wave, like a sonic boom. This compresses the gas as it passes, causing the gas to light up. When we look at it we see thin ribbons where the shocked gas is glowing. Like so:

That Hubble image was taken in 2000, nearly a quarter century ago. Note how thin the filaments are, marking the location of shock waves moving through the gas.

But in a new study, astronomers looked at images taken in 2020 and can see how far the shock waves have moved through the gas since an earlier set of observations in 2001 [link to paper]:

So cool! The new observations, in red, clearly show the shock wave has moved since the first image. I love how you can see that that wave has exactly the same shape but has been moving through the gas between the observations. Amazing.

They find that besides having the same shape, the shock is moving at the same speed it did two decades ago as well, which can give insight into the dynamics of how the supernova is interacting with the gas surrounding it. I’ll note that the entire remnant (that is, the huge circle making up the entire Cygnus Loop) is a staggering 90 light-years in diameter. We’re only looking at a small piece of a much, much larger tapestry of violence here.

Hubble has been in operation for 33 years now, and a lot of what it’s observed has changed (like baby stars shooting out beams of matter, or a dying star’s wave of ejected gas fading). The Crab Nebula has been seen to expand noticeably from observatories on the ground, too:

That’s from friend of the BAN Adam Block, by the way.

The Universe changes rapidly, even if the motion seems imperceptible by eye. But we have devices much more powerful and keen than just our eyes, and when we turn them to the sky we can watch the cosmos evolve.

It’s fantastic, and something I will always leave me in awe.

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My colleague Laci Brock is an astronomer and planetary scientist — she has a PhD, studying atmospheres of planets and brown dwarfs — and she’s also an artist. In the summer of 2022 she decided to take some time off from academia to work on her art. I’ve been following her on Twitter (though I’m using that platform less and less; she’s also on Blue Sky) since before that time, in fact, and the progress she’s made is pretty amazing. Her artwork is lovely. She’s done a lot of pieces on Jupiter, but has been branching out, and is working on one now based on the JWST images of the Eagle Nebula.

She is having a limited-time run on some of her work at her store, and you should take a look because it’s very pretty! And if you like something you see, buy it. Hurry! I mean:

Supporting artists is a universal good, but made even better when the artists use their art to communicate science like Laci does.

You can find her on Instagram and other various social media, too.

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!