Dying beautifully in a crowd

By Phil Plait | January 15, 2009 9:56 am

The Hubble Space Telescope folks just released a spectacular and surprising picture:

Hubble picture of the planetary nebula NGC 2818. Click to way embiggen.
Credit: NASA, ESA, and the Hubble Heritage Team (STScI/AURA).

First off, whoa. It’s gorgeous. What you’re looking at is a planetary nebula (it doesn’t have much to do with planets; these objects were named thus because they looked like planets through small telescopes). It was a star something like the Sun that reached the end of its life and blew off a strong wind of gas. Eventually, as more material left the star, deeper layers of the star got exposed. Eventually, the core was all that was left: a hot, small, dense object called a white dwarf. It flooded the nebula with UV light, ionizing the gas and lighting it up. The complex interaction of the gas and the radiation produced the shape and the different colors.

But NGC 2818, as it’s called, is an oddball. When I first saw this picture I didn’t even think it was a planetary nebula, I thought it was a much larger gas cloud that forms stars. The shape is not much like other planetaries! Usually they are round, or hourglass shaped. This one is squashed and weird. The colors are pretty much normal: the outer parts are loaded with nitrogen and are reddish, while the inner region is hotter, less dense (because late in the game the wind from the star got hotter and less dense), and glows blue due to oxygen. The fingers or towers pointing toward the center are due to the light and wind slamming into denser blobs of material. They’re a bit like sandbars that form in a current.

In fact, NGC 2818 does appear to be a bit different. I think the star that formed it (which should be right smack in the middle, but I don’t see much there; it might be hidden by one of the fingers) was more massive than the Sun. The wind speed is higher, indicative of a more massive star. The nebula itself is much larger than other planetaries; they are usually a light year or so across, and this one is well over three. The amount of different elements in the cloud also seem to say that this was a bigger and hotter star than usual, too.

What makes this guy most unusual, though, is that it appears to be inside an open cluster, a loose aggregation of stars about 10,000 light years from Earth. Most planetaries are loners, since they come from old, dying stars. The Sun has a ten billion year lifespan, enough time that were it born in a cluster it would have long ago drifted away. But NGC 2818 is located in a cluster, and the safe assumption is that this was where it was born. That means it must be from a relatively young star (or else it would have left the cluster)… and massive stars age faster and die younger than low mass stars.

So I think the star that formed this beautiful and intricate web of gas was a big one, maybe even close to the limit between where stars die this way, and explode as spectacular supernovae. I had never heard of this particular object before, and I’m glad astronomers got this image so that it can be studied more carefully. You can learn a lot looking at things that are up against the edge of two different behaviors, and investigating stars like this give us a lot of insight into what happens at that limit between going gentle into that good night, and raging against the the dying of the light.


Comments (47)

Links to this Post

  1. Dying beautifully in a crowd | MamentoMori | January 15, 2009
  1. ozprof

    Hi BA,

    Surprised you had not heard of this object. Maybe because it is in the southern sky! 😉

    It is one of my favourites and is on my list of 2’furs, ie 2 objects in the same view. Not a spectacular object in the eyepiece, but interesting.



  2. Another Dylan Thomas quote?? :)

  3. It blew off a strong wind of gas… That about sums up my life, sadly…

    One question, would these be the colours that we would see if we were close enough to observe this object with the unaided eye? It is absolutely beautiful

  4. Reid Alsworth

    Hey Phil, have you heard the new story about a possible discovery of evidence of life on mars? I was wondering if there was any truth to it. It had something to do with methane and water vapor.

  5. Now just imagine how much better this would look if it had been taken with ACS instead of WFPC2. I mean, if ACS were still working. Or, working again! Man, I can’t wait until May!

  6. idlemind

    Michael L: the image is false-color. In fact, the parts of the image that correspond to nitrogen (red) and hydrogen (green) are actually both deep red — only 2nm of wavelength separate these two atomic lines, a difference probably imperceptible to the eye. Furthermore, the human eye is so insensitive to dim red light that you’d probably not see it at all, but rather just the oxygen since its blue-green glow is right where the eye is most sensitive.

    Many of the most spectacular Hubble pictures of nebulae are false color, with green for hydrogen, blue for oxygen, and red for either nitrogen or sulfur, each viewed through filters that let through only the tiny sliver of spectrum where a particular species of ionized atom emits.

  7. This really looks like the stuff you see in the Eagle nebula (Pillars of Creation).
    I’m unsure of the scale here, so maybe this is a dumb question, but is there any chance that some of those “denser blobs of material” are planets that circled the star? Maybe distant Jovian-sized planets?

  8. I appreciate the explanation but I can’t get past the pretty. And I KNOW it’s false colour, can’t you just once let me live with the illusion? :)

  9. Torbjörn Larsson, OM

    a possible discovery of evidence of life on mars?

    Not AFAIU, but suddenly newspapers are pumping out a story before the science web caught up, on a Science online report on measuring methane and water vapor simultaneously with geographical and seasonal variation. It could be either geological or biological.

    Incidentally, the one mentioned locality, Nili Fossae, is both remarkable for being high on olivine (which AFAIU can emit methane by serpentinisation when in contact with water) and for being among the last dropped of potential Mars Science Laboratory landing sites. (It is a half open fossilized water table site, and they kept the closed ones and the half open Mawrth [aack!] Vallis.)

  10. It’s a perfectly cromulent image. Thnx.

  11. Torbjörn Larsson, OM

    Re my previous comment: BA’s sister blog The Loom has more on it, by liveblogging from a NASA conference with the lead author. The biological alternative is strengthened, for example:

    1. They can exclude other gases. So where is the rest of the usual volcanic emissions?
    2. Serpentinization is rare (on Earth) and have a secular time evolution: it plugs up the active sites over time.

    Exciting! And, as they point out, either way a methane (and water!) source is a food supply for small organisms, used in the very oldest Earth metabolisms to boot.

    Btw, NASA mentions that the MSL landing site selection process has “reset the clock” (probably since MSL is delayed), so these methane emitting sites are possible contenders again. Eg. at least the former candidate and now methane emitter Nili Fossae should be among the new potential sites.

  12. anonymic

    I’m terribly surprised that HubbleSite doesn’t mention what spectrum the photos are taken in, nor do they say how the picture is modified to show the minutiae of such things as the 2nm wavelength difference Idlemind mentioned. I thought these details were standard information to accompany such pictures. Thank you Idlemind for your explanation, though unfortunately your effort should not be necessary.

  13. Quatguy

    This methane/Mars finding is potentially huge. Phil, I would love to hear what you have to say about it. Perhaps you are researching it and will post later this afternoon?

  14. anonymic

    Strike that, it’s on the Fast Facts tab on the site. Though a simple caption such as “Filtered visible light spectrum” would be nice.

  15. Thanks for the explanation Idlemind!

  16. TBRP

    @ Mike Sperry

    There are no dumb questions: just dumb people, and those are the ones that don’t ask questions in any case.
    WRT your question, those blobs are probably anywhere from 3-1000 times the diameter of Pluto’s orbit, just based on Phil saying the nebula is 3 lightyears across, and my [very] rough guess on thier proportion to the entire bredth of the planetary nebula.

  17. kuhnigget

    Gorgeousness and gorgeosity made real!

    Planetaries are always my favorites. Maybe it’s the whole stellar death thing. I should’ve been a goth girl.

  18. “those blobs are probably anywhere from 3-1000 times the diameter of Pluto’s orbit…”

    WOW! ok, my sense of scale was WAYYYY off on this image. Each of those blobs could very well be its own planetary system then.

    I thought it looked a lot like the Eagle Nebula, with the proto-star system blobs streaming away.

  19. Seb

    Hi. I live in New York. And ever since I heard of the 2012 stuff I’ve been paying more attention in the sky. Everynight I see what looks like a star from different parts of the city…Is it possible to see the same star everyday? Thanks Phil or other friends.

  20. Ty

    What mechanism causes a newly formed star to wander away from its cluster?

  21. kuhnigget

    Seb, you are probably seeing the planet Venus, which is very bright in the western sky at night right now.

    Yes, you can see the same stars every day. They rise a little bit earlier every night, and likewise set a little earlier. Thus over the course of the year you will see the entire sky.

    Try going through some of Dr. Plait’s earlier posts, regarding 2012, which as soon as you do a little bit of background research you will discover is mostly nonsense. The Mayan calendar did not predict the end of the world, it was just based on very long cycles, the next one ending in 2012. After that, the old Mayans would have started a new cycle, just as we will in 2013.

    May I also suggest the website of Sky & Telescope magazine, which has terrific interactive star charts and great introductory information to new skygazers.

    Have fun, and stick to the real world…it’s much more interesting than any silly superstitions.

  22. KC

    NGC 2818 – I dub thee: the Clamshell Nebula

  23. KC

    >And ever since I heard of the 2012 stuff I’ve been paying more attention in the sky.

    Why? Are you expecting the sky to fall Chicken Little?

    Venus – you’re looking at Venus.

  24. Gary Ansorge

    Play nice. It was an honest question.

    I wonder if the original star will show up in the Xray range??? Should have been way hot enough for that spectrum.

    GAry 7

  25. SEB, there is a lot of nonsense out there about the 2012 thing… I’ve written about it on my blog (click on my name to get there) and I’ve posted some links to some straightforward sites about it.

    About that planetary nebula: the Hubblesite pages usually have a link to “fast facts’ and “more info” about given exposures and objects.

  26. KC

    G7: Part B was an honest question – Part A referred to bunk.

  27. KC: it doesn’t hurt to be a tad more polite.

  28. Sam Fisher

    Why do you act as if it’s surprising that this star was probably around 2 solar masses? This cluster is about a billion years old, to run of out hydrogen by that time, the star would have had to be at least 2 solar masses and that’s assuming it was formed early on. What is odd about this?

  29. Sam Fisher

    In addition to my comment above, if this was actually interesting, we could always check the turn off point for this cluster to tell for sure how old this star is but I don’t see why we would.

  30. Eris

    KC – “Part A” may have referred to bunk, but please notice that Seb didn’t say anything promoting the 2012 nonsense. He just said that after hearing about it he’s been paying more attention to the sky. And now he’s asking questions here trying to learn some more. Good!

    Welcome Seb!

    Seb – It’s sounds like you don’t get to see the sky very much. I live on the outskirts of Houston, and I used to live in it. Now Houston’s light pollution is pretty horrible, so New York must be even worse what with it having more than twice the people in less than half the area. So what you need to do is get out of the city some night. Head upstate into the country, or maybe up Long Island. The suburbs won’t be great, but once you get away from the big cities things are a lot better.

    You might also want to check out these guys: http://www.aaa.org/
    The Amateur Astronomers Association of New York. Since they are in Manhattan I’m sure they can tell you a lot more about what can be seen from the city than I can.

    And of course, NYC has a wonderful planetarium. http://www.haydenplanetarium.org/
    The Hayden Planetarium is run by Neil deGrasse Tyson, an astronomer who is a really good speaker and educator. Seeing a planetarium show is a great way to learn the basics about the night sky.

    So keep looking up, keep asking questions, and enjoy yourself!

  31. quasidog

    My new wallpaper for the week. :)

  32. DrFlimmer

    @ Ty:

    A cluster contains A LOT of stars. So gravitational encounters are quite commen. The stars will exchange a little bit of kinetic energy (one gets more, the other one has less left), so probably a star gets kicked out of the cluster (especially if it’s a low-mass star).

  33. kuhnigget

    KC: it doesn’t hurt to be a tad more polite.

    Yeah, there’s only room for one obnoxious commenter in these parts! Heh heh…er…?

  34. kuhnigget

    BTW, is anyone else getting really sick of the graphics in that microsoft Sync ad?

    I swear, I’m going to stick a piece of black tape on my screen….

  35. Cheyenne

    I’m so hoping for a post soon from the BA regarding the Methane find on Mars….

    My limited take on it is that there is probably no way to say for certain that it came from biological processes at this point – but it’s really good further evidence that there might be something there. And if there is it would be, well, wondrous.

    So, well, my old harp on is that we should launch some more probes there stat, get some robotic sample return missions in the works, and “let’s get this chicken cooked” (a Southerner said that to me – adorable them deep South folk). Screw sending people to the moon. Go find out if there is life on Mars NASA!

    ps- And that nebula is a really purty pic by the way. Hubble team is neat.

  36. Ty

    Thanks Flimmer.

  37. @Archie: Probably not any more dangerous than previous and future solar maxes. There is always the the possibility of a large flare or Coronal Mass Ejection during a max, but there really isn’t much we can do about it other than put satellites in safe mode(?) and send the ISS astronauts to a shielded chamber.

    Plus, if you look closely, that post was from Jan 8, 2008. i.e. a year ago. So far, the sun has been fairly quiet. You can check out solar activity at Spaceweather.com. They even have a link to a Daily Sun picture, showing day-to-day changes in the sun’s appearance.

  38. Asimov Fan

    So I’m thinking the precursor star for this planetary nebula was maybe about seven to eight solar masses to begin with .. a bright blue-hot B-type star … that sound right?

    Thanks BA. 8)

    Seb asked :

    “Is it possible to see the same star everyday?”

    Well there’s always the Sun – that’s a star that just happens to be really close! 😉

    More seriously, yes, stars rise and set over seasons , mostwillbe inthesky for many nights in a row – like months – but there are a whole group of stars that willalways be inthesky depending on your latitude. These are
    called circumpolar stars because they circle the South (or in the
    northern hemisphere North) Celestial Pole. (abbriev. SCP / NCP.)

    How many stars are in this circumpolar (pole circling) category depends
    on your latitude – if, like me, you’re at 35 degrees south then the SCP will be 35 degrees from the horizon and stars nearby (in my case, Alpha Centauri, Canopus, Achernar, the Large and Small Magellanic Clouds & more ..) will be visible every night, circling thepole. Youcan actually use them to tell the (approx.) time!

    In the northern hemisphere these stars will probably include Polaris (almost 100 %) the stars of Ursa Major aka the “Big Dipper”, (Dubhe, Alioth, Megrez, Phecda, Benetnasch, Alkaid) probably Capella, Vega, Deneb and more.

    The only exception? If you live on the equator where *all* stars rise and set – incl. the daily star known as our Sun! 😉

    (btw. From the poles *all* stars are circumpolar. From the South pole you can see Rigel but never Betelguese and from the north vice-versa.)

    I reccomend you find a starchart & / or planisphere, & visit a planetarium for more .. :-)

  39. Asimov Fan


    “More seriously, yes, stars rise and set over seasons, most will be in the sky for many nights in a row – like months – but there are a whole group of stars that will always be in the sky depending on your latitude. These are
    called ‘circumpolar stars’ because they circle the South (or in the
    northern hemisphere North) Celestial Pole. (abbriev. SCP / NCP.)”

    & QUESTION : Where did the two solar mass figure mentioned here come from?

    I understood this star was much more massive – in fact near the limit where stars go supernovae which is about 8-10 solar masses. Two solar mass stars -like Sirius, Altair, Fomalhaut, etc ..are much more common than those larger mass ones and are the ones behind your “average” PN which this isn’t!

  40. Bein'Silly

    Interesting title BA.

    It made me think some gymnast or diver had jumped off a tall building over some prominent crowded place, taking a while to land and doing some beautiful, 10-point backflips and sumersaults before hitting the ground! Or something like that! 😉

    Would that count as “dying beautifully in a crowd?”

    Or, alternatively, some really sexy stand-up comic doing a great routine to a crowd that just doesn’t get it or sumethin’ like that? 😉

  41. Joker

    @ Bein’Silly :

    “It made me think some gymnast or diver had jumped off a tall building over some prominent crowded place, taking a while to land and doing some beautiful, 10-point backflips and sumersaults before hitting the ground! Or something like that! Would that count as “dying beautifully in a crowd?”

    Not to the janitor or whoever it is that has to clean up the mess! 😉


    @ Joker

    It’s usually the Fire Department who has to hose down the sidewalk, afterwards! :-)

  43. Grant Bazan

    From what you described, it looks as though it may be a ONeMg white dwarf instead of a CO
    white dwarf. Theoretical models I used to work on could predict the existence of such WD’s only
    in certain circumstances (like wind models, convective overshoot etc …) very near the core
    collapse limit. I’ve never seen a PNe with a likely candidate. I’m anxious to see what comes
    from studying this object. Since I don’t do much astrophysics anymore, it won’t be me doing the research.

  44. Sam Fisher

    @ Asimov Fan

    “Where did the two solar mass figure mentioned here come from?”

    It’s the minimum mass needed for a star to become a white dwarf (and thus have a planetary nebula) with-in the life time of this cluster, I would revise that to 2.5 – did some more exact calculations this time.

    The star could have been up to about 8 solar masses as you noted, but there is nothing particularly special about this planetary nebula as you claim except for the fact that it’s in an open cluster and that only places a limit on its lower mass. So it’s really quite difficult/next to impossible as far as I know to tell exactly how old (and massive since that’s basically saying the same thing for this purpose) this star was.


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