Tears of a dying star

By Phil Plait | July 13, 2011 6:55 am

When I was a grad student, right before the launch of Hubble Space Telescope, I was fascinated by planetary nebulae, the weird, beautiful halos of gas surrounding dying stars. I still am! But back then, a big mystery was the transition stage between the period when a star expands into a red giant and blows this gas off, and the time the core of the star contracts, heats up, and lights up that gas by flooding it with intense ultraviolet light.

This stage, called the protoplanetary nebula stage, only lasts a few thousand years — pretty short on the galactic timescale. That makes PPNe rare and difficult to observe… but times have changed. Hubble has been up a while, and has spotted several of these uncommon beasts, like Minkowski 92:

Isn’t that lovely? The double-lobed shape is a pretty good indicator that the star in the center isn’t alone; it either has a companion star or was possibly circled by planets. When the star expanded into a red giant its rotation slowed, but if there were a nearby star or some planets it would’ve swallowed them up. While they slowly boiled away, they actually sped up the star’s spin like a whisk mixing up batter in a bowl. This created a disk around the star’s equator, and the gas blown off by the star flowed more freely up and down along the star’s poles, creating those lobes.

The gas is being lit up by reflecting the star’s light. Mostly, at least: if you look in the lobe on the left, there are faint filaments that are probably gas ionized by shock waves traveling through the material. Those are glowing on their own, but they’ll soon be outshone. In a few hundred or maybe a thousand years, the last gasps of the star will puff out the final bits of gas, exposing the bright hot core. This dense ball, called a white dwarf, will blast out UV photons and light the gas up like a neon sign.

Until that time, we can add Minkowski 92 to our very short list of these rare, delicate, and beautiful objects.

Credit: ESA/Hubble & NASA

Related posts:

- A star on the edge of a weird, lovely death
- The beginning of the end for a star
- Warm dusty rings glow around a weird binary star
- The knotty Cats’ Eye halo

CATEGORIZED UNDER: Astronomy, Pretty pictures

Comments (21)

  1. Kalle

    Am I the only one that thought about Bussard ramjets when they saw that image?

  2. The power of the Hubble telescope is amazing, it gives the whole universe to explore.

    Leamington Spa, England

  3. Cool. But, what gives it that “teardrop” shape? Why isn’t it a cone instead?

  4. Wayne Conrad

    Phil, The pictures you post are pretty, but your great explanations turn them from “pretty” to “beautiful.” Thanks for yet another beautiful picture.

  5. QuietDesperation
  6. Wow, amazing stuff. Kind of hard to comprehend at 9AM in the morning, but it definitely stretched my brain to read this and try to understand it. Thanks!

  7. Anchor

    The image shows what very much looks like a dusty disk obscuring the base of the background lobe. That is often seen in many examples of this type. Impeding disks should be considered as a prime candidate mechanism responsible for shaping these twin-lobed PN types alongside the more traditional idea attributing their morphology to the presence of binary companions and planets, which I’ve always found to be unconvincing and difficult to model consistently.

    Of course, the presence of either a stellar companion or planetary system is definitely not inconsistent with the presence of a dusty disk. In fact, many models suggest such dust disks are preferentially and even efficiently produced by aging binaries (a stellar companion to an aged red giant – which are often copious dust-producers – serving to gravitationally direct the outflow into a disk in the same plane as the binary) but it is far easier to see how such lobes are confined and collimated by such disks rather than by some vague constraining mechanism offered by compact objects like stellar or planetary companions in orbit around the star undergoing the upheaval. An impeding disk constrains an isotropic outflow quite naturally and disks are implicated in the vast majority of diverse bipolar jet phenomena. Why not implicate disks for these PN types as well?

    Oy, and there’s that horrible term again: “proto-planetary nebula”. It makes one wince. We should call them “Stellar Terminal Nebulae” [STN's], or “Terminal Nebula” (TN) for short; hence we may refer to a “proto-terminal nebula” stage without undue strain. Save ourselves hundreds of human-years of time and effort explaining to kids and the public that these objects don’t have anything per se to do with planets but for an unfortunate historical mistake that led to really Bad Astronomical Nomenclature.

  8. chris j.

    if the disk was caused by planets, would we then call it a planetary protoplanetary nebula?

    and if, by some freak chance, the nebula formed before the planets coalesced from the primordial disk, would we then call it a proto-planetary protoplanetary nebula?

  9. Here’s something I’ve often wondered when looking at all the beautiful pictures of nebulae…

    Let’s say you’re a deep space traveler and you have a spaceship that can take you anywhere in the galaxy. If you were to travel to Minkowski 92, or say, Eta carinae, how far away would you need to park your craft to get a really spectacular view encompassing much of the nebulae? Is it even possible to see them up close without specialized tools, or is the density of the gas so low that any effort to see them closer than hundreds if not thousands of light years away are futile?

  10. Greg Fish:

    Is it even possible to see them up close without specialized tools, or is the density of the gas so low that any effort to see them closer than hundreds if not thousands of light years away are futile?


  11. Anchor

    re: chris j. #8:

    [See what I mean?]

    No, chris, these “planetary nebulae” have nothing to do with planets or their formation or anything to do with “primordial” anything. These are OLD and dying stars or binary star systems billions of years after they formed.

    @#9 Greg Fish: The low surface brightness of most of the favorite objects featured in long-time-exposure telescopic images would prevent you from seeing very much with your naked eyes: ironically, as you got closer to such extended nebulas there would be a DECREASE of available photons coming from any given spot because the object would cover an increasingly large area of your field of view. You might catch glimpses of structure – faint tendrils, etc, as you sweep your gaze over it (say, from a distance of a few hundred light-years from the Carina Nebula, which would then fill nearly half your sky – that one is an enormous star-forming region, and although those gas clouds put out lots of emission, that light is very diffusely spread out: you might even have trouble seeing any color variations, although the famed and relatively very much tinier Humonculous Nebula enshrouding the supermassive star Eta might give you a fairly satisfying view from several dozen light-years because of its relatively much higher surface brightness. Of course the high-energy radiation would fry a person at such range).

    Alas, humans have evolved eyes with a maximum aperture of only 6 or 7 millimeters under a Sun that supplies very bright ambient light levels on the dayside of our planet, so we’re unsuited to fully appreciating the interstellar environment…but maybe long-term denizens of interstellar space have artificially engineered eyes that are meters across to collect and focus lots of faint light more suited to an appreciation of the interstellar environment in lots of wavelengths (=color). If we ever reach interstellar capability in the far future, we might similarly engineer ourselves. As a kid I wished I had Owl’s eyes: their view of the night sky must be gorgeous.

  12. Thanks Anchor! That pretty much covers what I wanted to know and all my follow up questions!

  13. Sam H

    @Anchor: Okay, I get how we shouldn’t always call every circumstellar dust disk a “protoplanetary” disk, but how is the term a mistake? If it’s a very young star then shouldn’t it at least be a semi-appropriate designation?

    Aussi: While I get that humans eyes would have evolved mainly for daylight and that the distances of interstellar space are so vast as to radically affect surface brightness, if these emission nebulae are powered by intense stellar radiation then I’m assuming that, even on a rouge planet in the heart of M42 one should still be able to see a moderate “halo” around the higher energy stars within the nebula, which may or may not be coloured. Then the planetary nebulae – when they are lit up by the white dwarf’s radiation, shouldn’t one be able to see a little bit of a glow if they were hiding behind a shadow shield, facing away from the dwarf. As for the Carina nebula – is the collective radiation really that strong from 100 ly’s distance? A little sad…I had plans for an epic SF novel which would end with the main characters stranded far from civilization on a small Earthlike world about that distance from the nebula, or at least far enough away to cause it to have a significant appearance in its sky with at least some colour.

  14. chris j.

    Anchor, you must have no sense of humor.

  15. Anchor

    Sam, the term “protoplanetary” isn’t a mistake and I have no problems at all with it. When applied to a young star, it works just fine – as in ‘protoplanetary disk’, or ‘proplyd’ for short).

    It can also work in cases where aged stars spawn a ‘new’ circumstellar dust disk, perhaps partially recycled with material from planets that have been absorbed by their host stars as they swelled into red giant-hood and regurgitated in the stellar wind as the core shrunk. If the disk lasts long enough, it is perfectly conceivable that such a renewed dust disk might form a set of essentially second-generation planets – in which case the term “protoplanetary disk” is again reasonable, accurate, and descriptively justifiable. (Planets have been known to orbit collapsed objects such as white dwarfs and even neutron stars).

    But we’re talking about “planetary nebula”, which are compact nebulae associated with the outflow of dying stars that have moved off the Main Sequence. In other words, stars that are TERMINAL stage of their lives. Near-death. I loathe the term “planetary nebula” because they do NOT have any explicit association with planets EXCEPT the vague resemblance of some of the spherical types to gas giant planets like Uranus and Neptune as seen through small telescopes, which is how the term originated to begin with during the 18th century.

    If the matter simply stood there, it would almost be okay, but the fact is we have since appreciated that ‘planetary nebulae’ evolve and undergo stages of development, so the obvious temptation is to place the qualifier “proto-” in front of “planetary nebula” to indicate a ‘planetary nebula’ in its early formative stage of development. (Like calling a dying man a ‘proto-dead guy’). The resulting “protoplanetary nebula” is the horrible result, since it so obviously invites confusion with the OTHER, far more reasonable use of the term, as in “protoplanetary disks”.

    But ‘planetary nebulae’ have nothing to do with planets, per se. Some ‘planetary nebulae’ may well be utterly planetless. Those whose host primaries that DO happen to possess planets (and probably more than half do, if estimates of the prevalence of planets from Kepler is any guide) may well tend to indirectly influence the morphology of the outflow, but such planets are never the direct CAUSE or source of material for the nebula we see.

    So, EVEN IF the circumstellar dust disk – however the host star comes by it – DOES survive the dying star’s death throes, and lasts long enough to condense into a planetary system, we face the hideous prospect of astronomers describing a protoplanetary disk within a protoplanetary nebula. Then people will inevitably conclude – MISTAKENLY – that these are objects which are specifically planet-makers. And the silliness starts all over again and we all (teachers, astronomers, etc) have to go through yet another aggravating round of corrective explanations to people and youngsters eager to learn what this stuff is all about, but can’t keep from getting hopelessly confused.

    Wouldn’t it be simpler and more clear to speak of a possible protoplanetary disk inside a proto-terminal nebula, with no suggestion that these Stellar Terminal Nebulae are THE PREFERRED places where planets form. If they were, most planets would reside in orbits around white dwarf stars and Kepler would surely not see so many planets and planetary systems around Main Sequence stars!

  16. Anchor

    Who can blame people for getting confused? I DO blame astronomers for not fixing something this chronically irritating and who instead thought it ever so much more important to wonder if Pluto is ‘properly’ to be considered a planet or not, which merely ended up as a semantic debate over the definition of what should have remained a generic word – namely “planet” – that has now ‘officially’ acquired lots of useless ammended baggage that pretends to specify what nature doesn’t even recognize as a ‘category’! A few months ago rogue planets was big news. Oh, WAIT! They CAN’T be called “planets” under the official definition ratified by the IAU. ‘REAL’ planets must have generally cleared their orbits of other planets and debris. Well, in the emptiness of interstellar space, they ply no orbit around any star and have no material to clear. The definition is not even wrong, or rogue planets aren’t planets.

  17. Anchor

    chris j., I suppose you must be right.

    My pleasure, Greg.

  18. I have been intrigued by planetary nebulae for some years. For my take on these dumbbell-shaped objects, see my site: http://campanellaacoustics.com/ange/index.htm. We need to put our modeling hats on because as far as I can tell, the “industry” isn’t.

  19. chris j.

    Anchor, i’ve wondered what would be a better term for these nebulae, and “terminal nebula” is a pretty good one that avoids the confusion of the original term and is not too technical.

    i recall many years ago, hosting public nights at a local observatory near wichita, and the question would always come up: “why is it called planetary nebula?” the ensuing brief history lesson is a guaranteed turn-off; people came to learn about and see the sky, not some mistake made by someone who wanted to call a planet “george.”

  20. CB

    A “rogue planet” not being a “planet” makes sense to me. A masterless samurai isn’t a samurai anymore, a disbarred lawyer isn’t a lawyer, and so forth. It is simply not the case that if the full description of something contains a word, then that word taken in isolation must also apply.

    Oh and I’d call a 5 orders of magnitude difference between objects on either side of the divide to be something ‘recognized’ by nature. It is nature which makes the distinction obvious.

    But you are right that they should correct this whole “planetary nebula” nonsense regardless of how it would make older texts even more confusing.

  21. Matt B.

    The picture kind of looks like Bender fulfilling his destiny.

    It’s nice to see someone use the correct past tense of “shine”, unlike in the denouement speech in Green Lantern (otherwise a good movie).

    Once again I’ll have to suggest that we use the term “world” when we need vagueness. Anything smaller than a (brown dwarf) star, and at least as big as B-612 is a world, no matter its orbit. So “rogue world” works.

    “Terminal nebula” is good. Or maybe “expanding nebula” in contrast to those contracting nebulae that actually have something to do with planets.


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