20 years ago today

By Phil Plait | February 23, 2007 10:02 am

Has it really been 20 years since Sanduleak -69 202 blew up? Wow.

Of course, that’s Supernova 1987A to you. And if that doesn’t ring a bell, this image might:

That image, from Hubble, was released as part of the 20th anniversary of the closest supernova in 400 years. It’s amazing– we know so much about this event now, and I know a lot of people — including me — who would have killed for this knowledge back in, say, 1990. But we still don’t understand a lot about it too.

If you want a history of this object, I won’t belabor it here, since I have details in an article I wrote about 87A. In fact, that is the first part of a series of short articles I wrote about the supernova (at the end of each is a link to the next). But the early days were very confusing. It was thought only red supergiant stars could explode, but this one — named Sanduleak -69 202 — was clearly blue when it detonated. It emitted ultraviolet light as expected, but the amount was weird– it got brighter and fainter in an odd way, as if it had a cloud of gas around it. The best images we could do, pre-Hubble, did show some sort of elliptical envelope of gas, but the UV light didn’t match the shape seen.

It wasn’t until we got the Hubble images in 1990 that we saw that inner ring, and things made a little more sense. We could see that it wasn’t a complete shell (like a football), it was a flat ring! But then we realized we still had a problem: how did that ring get there? And what were those fainter arcs above and below it?

I was in the thick of it back then. I had just started my PhD research, signing on with a large project to look at exploding stars with Hubble. I signed up just before launch, so I got to live through the trauma of learning about the flawed mirror, and getting the fuzzy data. I spent months learning how to clean up the data, and wishing for just a few more photons, and lying awake at night (after getting our first meager data on 87A) staring at the ceiling trying to figure out just what the heck that ring was.

Lots of false starts. Lots of dead ends. Lots of great ideas smashed by reality. Lots of math. Lots more math. Lots of meetings, lots of talking, lots of sitting in front of a computer learning about deconvolution, pointing constraints, spectral analysis, Fortran, IDL, Unix.

In the end, I was able to cobble enough together to write a scientific paper and get my PhD in 1994. A lot of what I (and my collaborators of course) were able to figure out turned out to be right, and some turned out not to be. No matter how you slice it, Supernova 1987A is a weird object. For a long time we knew of nothing else like it, but eventually (really, quite recently) people found similar objects. Not that we understand how you can get those three rings like that– that’s still a mystery, even after 20 years.

Wow, 20 years. Well, the Universe ticks on. During that time, the inner ring faded as the initial blast of light from the explosion wore down, but then it rebrightened years later as gazillions of tons of hot gas from the exploded star begin to reach the ring. The supernova itself was at first an unresolved dot, but as you can see from the image above it’s expanded greatly over two decades. It’s an elongated cylinder of material now, getting bigger every day.

And it won’t stop, not for thousands of years. After 7305 days, it’s stretched out to be a goodly fraction of a light year, but it’s still screaming along at thousands of kilometers per second. It’ll slam into the inner ring, eventually dispersing it (that’ll take decades, probably). A few hundred years later it’ll reach the outer rings, and blast them apart too. Maybe eventually it’ll look like the Crab Nebula; there’re some indications the explosions were a bit similar. Even then it’ll go on, getting bigger and fainter, looking like the Vela remnant, and then Simeis 147, and then it’ll fade, mix, and merge into the ambient gas surrounding the other stars in the outskirts of the Tarantula nebula, where the star that made the supernova was born. No doubt by then more of the stars in its neighborhood will blow up; the place is lousy with massive stars just waiting to go off. They’ll have their turn, and future astronomers can marvel over them, as well.

I hope they have as much angst, sleepless nights, head-scratching, wonder, joy, awe, and fun as I did looking at Supernova 1987A. Isn’t that the point?

Note added after I edited this, but before I posted it: Amazingly, while looking up some info about the star that exploded, I stumbled on the announcement that the mystery of the origin of the three rings may be solved! It’s been speculated for a while that the star that blew up was originally a binary star, two stars orbiting each other. If one was more massive than the other, then it could have literally swallowed the smaller one up when it expanded into a red supergiant (it turned blue later). The smaller star spiraled into the bigger one, eventually reaching and merging with the more massive star’s core. As it spiralled in, it "spun up" the more massive star, making it rotate faster and flattening the equatorial regions into a disk. That’s how the inner disk may have formed. Eventually, much of the outer gas of the merged stars was ejected in various stages, and the complicated ejection mechanism may have formed the outer rings. New models by Podsiadlowski, Morris, and Ivanova appear to confirm this idea mathematically, which is fantastic news! It’s not 100% certain, of course, but it’s a great step toward understanding. And that, most certainly, is the point.

Update (late on February 23): the wonderful and talented Jennifer Ouellette, whose name I cannot type correctly on the first try no matter how much I want to, has much more meaty info on this.


Comments (19)

  1. Cindy

    I remember being a undergrad at Penn in 1987 and hearing that neutrinos were detected from SN1987A!

    That’s cool about the absorbing the companion star.

  2. Gary Ansorge

    That’s a fantastic image!

    Gee, maybe the rings are energy collection devices to make ZPMs for SG Atlantis?


    Great work there, Phil.

    Gary 7

  3. Wow, that picture blew my mind. Those explosive expanding rings transcend Saturn’s rings for a second. Of course when the excitement wears off Science must take over.

    Congratulations on your PhD, and, you are very lucky not to have picked a dry subject. You must concentrate again on Supernova 1987A. Your post is fine for information generation. Please publish again with a most serious book format.

    This astronomical object is not a “three-ring-circus”.

  4. Tom epps

    Phil, I remember when this one cooked-off…the media was all over it and I was lucky enought to be in Australia on business at the time–with my 90mm! We were out every night checking it out, and tracking the coverage. My best friend’s fiance asked if we were crazy–“it’s just a star!”

    Perhaps the most amazing thing is that they are still married, twenty years on…

    Thanks for the trip down memory lane!


  5. wright

    Wow, rings on a stellar scale. Magnificent. The universe is such a beautifully bizarre place.

  6. jess tauber

    Tarantula Nebula lousy with stars waiting to explode, the Milky Way lousy with dust- am I seeing a pattern developing? Linguists- feh!

    Jess Tauber

  7. I remember that like it was 20 years ago. :)

    Seriously, I do remember hearing about it, and a friend of mine in Australia sent me some photos he took the day after the SN was reported.

    I just used his images in an article I wrote about SN1987A for my local astronomy club’s newsletter.

  8. ioresult

    Cindy said: “I remember being a undergrad at Penn in 1987 and hearing that neutrinos were detected from SN1987A!”

    And I was in high school at the time and I even remember reading in a science magazine that the neutrinos came a few hours before the supernova! (now I understand why, but not back then)

    Also, I hope that the last picture Hubble takes before being decomissioned is going to be an extreme zoom-in of 87A.

  9. tacitus

    What we really need now is a supernova or two in our own galaxy, not too close, mind.

    If one exploded on the other side of the galactic center, would we know about it? Would the blast of neutrinos make it through the bulge?

  10. dkary

    The neutrinos would make it through damn near anything, the bulge included.
    We would probably also get the X-rays from it, and prossibly something in the radio.

  11. icemith

    What I can’t understand is if the neutrinos precede the light from the supernova event by a few hours, after travelling for 168000 years, and that they pass through almost everything, but a very few are “caught” by the instruments, (I believe huge tanks of water (heavy?) deep underground), how is it determined exactly what is their origin?

    Do they have little tags, or is the timing retrospectively determined? I realise that those neutrinos are products of the very first ignition sequence so to speak, but could they just be passing neutrinos at the exact time the supernova occured. It is reported that only 24 have been identified out of an estimated 10^58 power, being 99% of the mass of the original star(s)!

    I worry about sample size, but not the time difference suggesting they travelled faster than light, just that they had a head start. It seems that if a nearby S/N occured, we would have just less than three hours to get our affairs in order, if the “neutrino watch” program was active. Not that we could hide anywhere though, before the Earth was seriously compromised!

    Any other ideas?


  12. Gary Ansorge

    Light (read electromagnetic radiation) gets reflected, absorbed and re-emitted by the gas cloud surrounding the star, neutrinos pass straight on through. Which is why the neutrinos get here first.

    Gary 7

  13. Gpplascencia

    Has it really been 20 years since Sanduleak -69 202 blew up? Wow.

    ehhh… wouldn’t it be something like “Has it really been 20 years since we saw Sanduleak -69 202 blew up?” It didn’t blew up 20 years ago, but long before that. We just saw it 20 years ago. How many light years away is Sanduleak?

  14. Gary Ansorge

    About 169000 LYs, give or take a few

    GAry 7

  15. Irishman

    Gee, Phil, I can’t believe you missed that very prominent Angel in the new picture above. Right smack dab in the middle of the purple. Or is that a face? ūüėČ

  16. Florian

    20 years already? Geez, I’m getting old. /-:

    I had a look at the paper you linked to in your post. Not that I understand that much of it, being an engineer. *g* But why are centimetres used as a unit of length? On an astronomical scale, this looks rather odd. (Ok, better than, say, feet or furlongs q-: )

  17. StevoR

    Correction :

    Any sign yet of a neutron star or black hole left behind by the collapsed core of Sanduleak (set of numbers!) ? ūüėČ

    Isn’t _that_ one of the great mysteries about SN 1987A – that no stellar remnant as expected for a type II supernova has been found?

    My typing is usually bad –the later it gets the worse it gets –& I honestly don’t seem to see the typos until after I’ve clicked submmitwhentheyall jump rightout at me! :-(.

    BA, Mr Phil Plait, sir, : if I’ve one gripe about this otherwsie awesome site -its this – Can’t you add an editing capability to these comments sowe can go back & correct ’em? Please. Please, pleasepleasewith iionised H alpha & O III on top? (Hmmn.. now that wouldn’t work -beinglighter teh Halpha would have togo above .. a-n-y-w-a-y …

  18. Harvey

    The star didn’t blow up 20 years ago. The explosion took place a long time before that; it was 20 years ago that it was visible from earth.

    I think the next star to blow up will be Tom Cruise. Just a guess.


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