Hubble snaps a dead star on the rise

By Phil Plait | March 31, 2008 9:58 am

The spiral galaxy NGC 2397 is more than just a pretty face… though it is a very pretty face:

Spiral galaxies have lots of gas and dust in their spiral arms which actively form new stars. Some of these stars are very massive and bright, and can be seen as individuals in Hubble images like this one. Massive stars don’t live long, exploding as supernovae after only a few million years. Images like this one can prove invaluable when such a star explodes; we can go back and look for the star itself in older images and learn more about it.

As it happens, the astronomers taking this image of NGC 2397 caught a supernova just as it was starting to brighten! That’s a cool coincidence, and very helpful; observations of supernovae before they get really bright are hard to come by.

So where is it in the image? It’s not either of the two really bright stars you see; those are both nearby stars in our own Milky Way. Actually, the star would be impossible to find without already knowing where it was (click to embiggen, as usual):

It doesn’t look like much… but that’s because it was caught early. Supernovae explode with so much energy that they can actually equal the brightness of an entire galaxy! So no doubt a few days later this nondescript star located in a galaxy 60 million light years away became a heckuva lot more noticeable, at least to any aliens local to NGC 2397. From Earth, it never got terribly bright, only about magnitude 15.6, or 1/10,000th as bright as the faintest naked-eye star. Still, that’s bright enough to be well-studied.

One other thing: once a star explodes, it’s very hard to know much about what it was like before the titanic event. The astronomers who made this study of supernova host galaxies have made an amazing discovery: stars as lightweight as 7 times the mass of the Sun can explode! That’s lower than previously thought, and makes me wonder; perhaps the star in that case had erupted previously, losing most of its outer layers, exposing just its core. When that exploded, it would be an underluminous supernova coming from what looks like an undermassive star. In reality it started out very massive (20 or more times the Sun’s mass) but lost a lot of weight on its way to exploding. I couldn’t find a paper online with any specifics, so if anyone knows about one (the lead author is Stephen Smartt) please leave a comment! In the meantime, I’ve emailed him and I’ll post a response once I get one.

Comments (20)

Links to this Post

  1. Itty Bitty SuperNovae « AstroGeek | April 1, 2008
  1. Dan

    I have no idea how you manage to see what it is that you see. All I see when I look at that spiral is a collection of bright stars and gases and whatnots.

    How do you feel about dusting, Phil? I mean, with your eyes and attention to detail and ability to see the minutest of particles, you could probably do an amazing job, and my house really could use a cleaning.

  2. That’s why astronomers would make excellent maids. I’m intrigued by Phil’s theory that the star could have previously been much bigger and in fact it wasn’t a smaller star that exploded in the first place. I’ll have a look and see what I can find.

  3. BlondeReb3

    I wish someone had caught a photo of the star at its brightest. I would like to see what it looked like in the galaxy.

    And some supernovae can be as bright as the galaxy itself? I don’t even know how to react to that. That would be amazing!

  4. Alan

    “The astronomers who made this study of supernova host galaxies have made an amazing discovery: stars as lightweight as 7 times the mass of the Sun can explode! That’s lower than previously thought…”

    But, but, but….that means they’ve found evidence that an hypothesis in their scientific field might need updating….but….scientists don’t do that, right? they just cover up evidence that conflicts with their “belief” ….

    Oh wait, that’s in the Bizarro universe that exists in the minds of Kent Hovind and Ben Stein. In this universe, it’s cool to see people still finding things we need to learn more about. :)

  5. Chip

    BlondeReb3 writes: “I wish someone had caught a photo of the star at its brightest. I would like to see what it looked like in the galaxy.”

    If Phil’s conjecture is correct, you’re probably thinking of this star when it initially exploded as a much more massive star. This might have happened long before humans were looking at the sky, however I would guess (or hope) that someone is also researching old photographic plates of this galaxy. Some very old observatory photos (1890s through 1930s for example) are remarkably detailed. It would be interesting to see if the star can be spotted.

  6. This is one of the best pictures we have of a supernova in progress. It’s not as bright as the *whole* galaxy, but it’s still awfully bright:

    http://apod.nasa.gov/apod/ap000312.html

  7. Chip

    I didn’t find a paper though I did find that Stephen Smartt does research in the detection of precursor stars and/or “Supernovae Progenitors”. He contributed to the article “A giant outburst two years before the core-collapse of a massive star” published in Nature in 2007.

  8. Scott

    I was just wondering if anyone (Phil in particular) knew the name of the galaxy that can be seen to the right of the image. It looks like we’re getting a pretty much top down look at it’s spirals, and it looks amazing. Any bigger picture of it on its own.

    The link to the larger image at the Hubble website isn’t working (for me at least) so I can’t check there.

    Cheers
    Scott.

  9. “I was just wondering if anyone (Phil in particular) knew the name of the galaxy that can be seen to the right of the image. It looks like we’re getting a pretty much top down look at it’s spirals, and it looks amazing. Any bigger picture of it on its own.”

    Isn’t it 2397A? I could be wrong but it’s all I could find near it.

  10. Scratch that, it’s way too close to be that.

  11. Ok, I’m pretty sure it’s NGC 2466.

  12. NGC 3314

    No, 2397A is 7 arcminutes to the south and way outside the HST field (which is shown just about with south at the top). This face-on spiral is surely uncatalogued to date (it shows up only as a poorly resolved smudge on the digitized ESO/SRC survey photographs). And it’s in the wrong part of the sky (declination -69) to appear in the Sloan survey.

  13. Mapnut

    What am I missing? I don’t understand what the “dead star” in the title refers to.

  14. A star becomes a supernova when it ceases nuclear fusion in its core. This can be referred to as a “dead” star.

  15. slang

    From the linked ESA article:

    One atypical feature of this Hubble image is the view of supernova SN 2006bc taken when its brightness was on the decrease.

    (emphasis mine). BA, you wrote that it caught the supernova increasing in brightness, which would indeed be pretty awesome. Which is it? Increasing or decaying brightness?

  16. This was a type II (core collapse) supernova. Is this particular supernova one of the ‘lightweight’ ( < 9Msol ) ones they found, or is that just one of the overall conclusions of the study?

  17. I think there’s a little of confusion.
    Even if the Smartt’s work is to study the precursor of supernovae, this Hubble image pictures the supernova in its late stage. Indeed, the supernova was discovered in March 2006, while the Hubble image was shotted in October 2006.
    So, the image shows the SN when it was actually decreasing in brightness.
    Davide

  18. I know that there can be a tremendous amount of blowoff in a red giant’s solar wind, amounting to an appreciable fraction of its mass over time, but it’s hard to believe a star can go from 20 solar masses to 7 just by blowoff. What are other people saying about the model in this paper, or is it too recent?

  19. Patrik

    The PGC2005 catalogue has PGC 281862 at about the right place and with similar (at a glance) properties.

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