I’ve always been fascinated by supernova remnants, the expanding gaseous debris from a star that exploded. We know of quite a few within a few thousand light-years of Earth. Many are compact, like the famous Crab Nebula, and some are more diffuse, like the Vela and Veil nebulae.

The gas expands away from the supernova at high speed at first — several thousand kilometers per second — but as it plows into gas and dust between the stars it slows down. That material piles up like snow in front of a plow (this is actually called the snowplow phase) and the gas eventually stops expanding and mixes with the interstellar material that was already surrounding the star before it died.

Remnants can take on many shapes. Many are roughly spherical even after thousands of years when they’re dozens of light-years across. They take on an odd structure, though. The gas between stars sometimes forms sheets, which get highly compressed as the expanding debris rams into them, and they break apart into long, thin tendrils. That’s not too surprising, but then you see something like the nebula SNR G13.3-1.3 and you’re like, what the WHAT?

SNR G13.3-1.3 was discovered in 1995 in an X-ray image of the sky; supernova remnants are commonly sources of high-energy X-rays. The gas can have strong magnetic fields embedded in it, and these can capture and constrain charged subatomic particles like electrons. As the electrons spin around the magnetic field lines they emit radiation, including X-rays.

The distance of SNR G13.3-1.3 from Earth isn’t well known, but likely around 10,000 light-years. In the image, red is light from hydrogen gas, and blue is from oxygen [link to journal paper]. The diffuse hydrogen may just be material between the stars and not affiliated with the remnant. You can see the outer edge of the supernova nebula in the curved red arc of hydrogen on the left. 

The oxygen, though… tendrils like those are sometimes seen in nebulae like this, but why do they appear to diverge away from a point on the left, becoming more diffuse as they do? They look like outstretched fingers, or lightning bolts tens of trillions of kilometers long.

A close-up of the tendrils in the linked paper show they tend to be more sharply defined on their bottom edges and more diffuse near the top. As the authors note, this suggests we’re seeing sheets of material edge-on. The thin sheet is well defined because it’s at the edge of the expanding debris cloud, but when you look away from that sharp point you see more of the bent sheet through the debris itself, so it looks more diffuse. I’ve described this sort of effect in The Old Blog. It’s an edge effect, like looking at a soap bubble. The outline of the bubble is sharp, but looking toward the inside you see more dispersed material.

But I’ve never seen anything like these! The authors note that other examples of similar tendrils have been seen, but I don’t really understand why they seem all converge at one point. It could be some sort of weird perspective effect, but it may also just be multiple nearly parallel sheets of gas being lit up. I’m having a hard time picturing that, though.

The authors also note the diffuse blue light from oxygen on the lower right doesn’t have a clear explanation. Why is this gas dispersed that way? No one knows. That’s fun! It’s always interesting to find something puzzling, and try to work out why it may be that way.

This image was taken along with 11 others in a survey of supernova remnants undertaken by Robert Fesen and a team of “amateur” astronomers, including Marcel Drechsler, Xavier Strottner, and Yann Sainty, about whom I’ve written before [I’ll note Bray Falls is on the author list as well; I’ve been following him on Instagram for quite some time]. They take exceptionally deep images of the sky with small telescopes (or just telephoto lenses) just to see what’s there.

This hasn’t really been done before in the light oxygen emits, so it’s actually not much of a surprise that there are surprises there, ironically. Professional telescopes tend not to be used to look at extraordinarily faint objects because it takes up too much time. Also, many of these objects are too big to see with a big ‘scope (G13.3 is over a degree across, twice the apparent size of the Moon on the sky!). With the amazing quality of equipment and processing now available to skilled amateurs, these very faint buggers can be seen.

Amazing. It’s worth looking at the journal paper; I know the technical details are, well, technical, but the images are just fantastic. It’s well worth scrolling down to see them all.

I’ll add that supernovae create heavy elements, forged in the nuclear fires of the explosion. Literally we owe our existence to them, since they create elements like oxygen, calcium, iron, and others that are necessary for life. They also affect huge volumes of galactic space, and the cores of the exploding stars make neutron stars and black holes, too. That’s another reason I love these things: there’s something for everybody.

Tip o’ the dew shield to AAS NOVA, a site that highlights interesting research. They always have fun write-ups and links to cool stuff. I read it every day.

I was interviewed about my book Under Alien Skies by my colleague Mat Kaplan from The Planetary Society for his book club podcast. It’s on YouTube if you want to watch it (or I’ve embedded it below). It’s a wide ranging interview, and we cover a lot of fun topics. Enjoy!

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