Truly weird JWST images of a truly weird object: Supernova 1987A

September 4, 2023   Issue #612

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

Oh, I’ve been waiting a long, long time to see this: JWST finally observed Supernova 1987A!

Check THIS out.

Yeah, bizarre, right? And I’ve known how strange this object is for a very long time now…

SN 1987A (and those in the know call it) was once a blue supergiant star, far more massive than the Sun, in the Milky Way’s companion galaxy called the Large Magellanic Cloud (or LMC). It’s about 170,000 light-years away, give or take. Thing is, it blew up. Done exploded. Bang! Supernova.

The light from this event reached Earth in February 1987 (hence the name), and it’s no exaggeration to say it revolutionized astronomy. The brightest supernova in 400 years*, pretty much every telescope on and above (and even under, since it was detected by neutrino observatories which are underground) the planet turned their eyes to see what they could see, and they saw a lot. Back on my Very Old Site I have a bunch of articles I wrote about it; you can start with this one and each links to the next in the series at the bottom.

I studied Hubble images of this object for my PhD, so it’s very gratifying and amazing to see images of it from JWST! But what the heck are we seeing?

[Let me start by saying no paper was released with this image, so my descriptions below are based on the image itself, what I know about JWST, and my studies of the weirdo nebula around it over the years. Fairly warned be thee, says I, and this with an earth-mass of salt.]

The bluish blob in the middle shaped like a keyhole (or, better, a Goldfish cracker) is the expanding debris from the explosion, the outer layers of the star torn apart and flung outwards by the event. Moving at a decent fraction of the speed of light, it’s grown visibly over time (Hubble images taken over the years show this very dramatically). It’s colored teal here, which means the light you’re seeing is at a wavelength of 1.64 microns, using a filter that preferentially selects light from glowing iron. When stars explode they make a lot of iron, so that tracks.

Here’s where things get tricky. Before it exploded, starting maybe 20,000 years ago, the star started blowing out a complex wind of material. For reasons we still don’t know, the star must have either been rotating rapidly or was surrounded by a thick disk of gaseous material over its equator. The winds couldn’t push against it, so they inflated upwards and downwards, creating a huge hourglass-shaped double-lobed structure. I do mean huge: It’s roughly 5 light-years across. Immense. It’s tipped to our line of sight by about 45°. We see it best around its edges, like a soap bubble, so it looks like a pair of intersecting ellipses with a brighter, thicker ring in the middle. This diagram might help you picture it.

The elliptical ring of dots around the expanding debris is part of that thicker inner ring, the origin of which is still unknown despite being studied for more than 35 years (and a brilliant paper on it). The ring is made of gas including hydrogen and oxygen, and is over a light-year in diameter. It’s clumpy, and when the shock wave from the supernova hit it the clumps lit up like a string of pearls.

It looks like the debris itself is about to hit the ring at the top and bottom, but that’s an illusion of perspective. We see it at an angle, so while it looks like the debris almost overlaps the ring, look at the sides: That’s the stuff in the plane of the ring, and it’s well inside the ring (think of it like a football that’s vertical inside a horizontal hula hoop). It’ll be decades, I suspect, before that debris slams into the ring. That’ll be a thing to see.

All the fuzzy orangey stuff around the ring is hydrogen gas (given the color, it was taken using the 4.05 micron filter, which selects for infrared light from hydrogen). We saw hints of that in the Hubble images, which at the time I speculated (in the early 90s!) was gas above the plane of the inner ring, possibly in the hourglass structure. I’m still not 100% sure what it is, but I think it might be gas blown off by the star before it blew up, now being hit by the explosion shock wave. Totally guessing here. The whole structure might be filled with gas like that but we don’t see it because the shock wave hasn’t driven out that far yet. Again, I’m speculating. Hopefully a paper will come out with a more data-driven diagnosis.

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The press release notes two very faint crescents of material color-coded blue inside the ring, which are pointed out in the annotated image above on the right. These may be the leading edges of material blasted away by the explosion. It’s hard to say what their 3D structure is. The material could be a giant ellipsoid, like a rugby ball. If so — and there’s reason to think that, since the inner debris is extended above and below the plane of the ring — the crescents may be edge-brightened like a soap bubble (I’ve explained this sort of thing before).

I’m having a hard time interpreting this, but it could mean the outer edge of the debris actually is getting very close to the inner ring. This material will be pretty thin compared to the denser goldfish stuff, but when (if) it hits the energy it’ll deposit into the ring will be huge. The ring’’ll light up like Clark Griswold’s house at Christmas.

This stellar explosion taught us vast amounts about how massive stars end their lives. For me personally one of the biggest impacts it had on me — besides getting my degree and all that happened because of that — was seeing how objects can change over really very short periods of time. I could see differences immediately between images we took just a year or two apart! Now it’s been over 35 years, and the changes in this weird structure are incredible… as has been our evolving ability to observe it. We get better at this all the time, and I’m glad I’m around to watch it unfold.

* Mea culpa: I originally wrote that this was the closest supernova in 400 years, but I forgot about G1.9+0.3! It exploded on the other side of our Milky Way, and its light reach us a little over a century ago, but was obscured by so much dust that it wasn’t discovered until recently. No one on Earth saw it at the time because it was far too faint. Thanks to BANner Scott Harrington for reminding me of this!

Et alia

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