One ring to fool them all

By Phil Plait | June 5, 2008 8:01 am

It’s a mystery. I don’t like mysteries! They give me a bellyache, and I’ve got a beauty right now…
—Captain James T. Kirk

Planetary nebula are beautiful clouds of gas that form when stars like the Sun die. The star blows off a series of super-solar winds, ejecting gigatons of gas into space. As this happens, the star itself exposes its hot, dense core, which emits scads of ultraviolet light. This high-energy light ionizes the gas, creating what is essentially a cosmic neon sign a few trillion kilometers across.

These nebulae take on weird shapes depending on lots of factors. Some have binary stars in them, for example. As the stars orbit each other, they tend to emit gas preferentially in a flattened sphere, like a basketball someone has sat on. The nebula takes on an ellipsoidal shape, and sometimes even an hourglass shape. If it’s the latter, you can see a bright ring surrounding the central stars, which is the waist of the hourglass.

Behold the planetary nebula SuWt2, located 6500 light years away. That’s it in the image above, taken in 1995 from a 1.5 meter telescope in Chile. You can see the ring which is the hourglass waist, and just make out a little bit of the lobes of the hourglass; at least near the central ring (deep exposures show more).

But there’s a problem. The gas is lit up, so one presumes the bright star in the center is what’s doing the illuminating. But if you study that star, you run into a major problem.

For one thing, the star isn’t a star. It’s two stars. That’s OK, and even good: that would explain the shape of the nebula. But the major monkey in the wrench is that neither star is bright enough or hot enough to do the job. They’re A stars, meaning they’re hotter and brighter than the Sun, but not enough by a long stretch to power the nebula. They simply don’t have what it takes to make the gas so bright.

Usually, the star in center of a nebula like that is a white dwarf, a compact, dense, hot object leftover when a Sunlike star sheds its mortal coil. So seeing two normal stars there is weird. It’s like hearing a dog barking behind a door, and opening it to see a squid*.

So where’s the white dwarf? I’ll cut to the chase: we don’t know.

Possibilities:

1) It faded away. White dwarfs don’t generate energy any more, so over time they fade. However, that usually takes a long time, like millions or billions of years. The nebula can’t possibly be that old; such objects are a few thousand years old. So that seems unlikely to me.

2) It might be hidden. Before the star died, it would have shed lots of dust, which can enshroud it. That seems unlikely as well; it would take a lot of dust to do that.

3) Or maybe, along those lines, the binary is hiding it. Maybe the binary is not associated with the nebula; the pair of stars just happens to be sitting in the way. If that’s the case, their light might be overwhelming the white dwarf.

Except… a telescope that sees UV light saw no sign at all of any white dwarf, or any star that might be zapping the gas. The binary wouldn’t be able to hide that.

This is really weird.

As it happens, the hourglass shape is something I’m familiar with: Supernova 1987A had one around it. The star that blew up had previously created the giant structure, then lit it up when it exploded. Interestingly, the explosion seems to have left nothing behind; even after more than 20 years there’s no sign of the usual neutron star or black hole.

It’s difficult to see how that ties in here, though. Had the star that formed the SuWt 2 nebula exploded, it would have been spectacularly bright at its distance of only 6500 light years. And if it happened too long ago (long enough that no one happened to notice it, like thousands of years ago), the nebula would have been torn apart by the debris by now.

Since I have some experience with planetary nebulae, I talked to the two astronomers who released this news, Howard Bond and Katrina Exter. They’re baffled by this object, and we had a jolly good time tossing around ideas. I have to wonder… the binary stars do appear to be in the center of the ring, or close enough. And they’re weird too: they rotate too slowly, as it happens, and they appear to have almost exactly the same mass, and they both appear to be at the same stage in the life, and that happens to be where hydrogen fusion in their core has stopped, and they’re contracting and heating up.

So it makes me think that if you have a weird object, and the stars in the center happen to be weird, then maybe that’s correlated. But none of us could figure out how. So in the end — or at least, wherever we are now with this bizzare thing — we just don’t know what’s generating the energy needed to light it up. Unlike the movies, not all scientific puzzles get wrapped up neatly at the end, with the scientists laughing and clinking their glasses together as the credits roll.

But still, unlike our dear Captain Kirk, we do love a mystery. So we’ll keep at this one, and I just bet one day I’ll be posting about SuWt 2 again, and I’ll have an answer for you.



*And may I add how distasteful that would be.

Comments (73)

  1. Rowsdower

    It may be a mystery, but it sure makes for a pretty picture, too. Thanks!

  2. aiabx

    I don’t like mysteries. I like *solving* mysteries. And this is a good one. I wonder if it’s being illumnated by another nearby star unrelated to it?

  3. RL

    Cool quote, BA. Maybe this mystery will shake up some previous understandings. Or signal a new type of object to be discovered! Thats always cool, too.

  4. You say the binaries “rotate too slowly.” I take it you mean the entire system of two stars rotates and not the speeds at which the revolve around each other. Another “invsible” body just far enought to slow them down? Or, just blame it on dark matter.

  5. Kesstra

    Just out of curiousity is gravitional lensing a possibility?

  6. Celtic_Evolution

    Wow… what interesting (not to mention astronomically cool) puzzle…

    Assuming that the two stars in this case are not hiding the actual supernova star(s) and are in fact at the center of the nebula, I have a few questions for clarification, please… forgive me if they seem like simplistic / uneducated questions.

    First, you mention that this being a binary would explain the hourglass shape of the nebula… wouldn’t this only be true of both stars in the binary went supernova? Or am I drawing an incorrect conclusion regarding the shape?

    Second, do binary stars generally both go supernova at the same time? And would that make a difference here in any case?

    Third, could the interaction between the two stars be causing the observed effects? Especially of one star is significantly larger than the other?

    And lastly, are these stars located in any known gaseous region that might have an impact?

  7. Andrew

    Celtic_Evolution:

    I assume that it’s the gravitational interactions of a binary system in the first place that explain this shape. It’s not so much that both stars went nova, and that created two lobes, as it is that the binary pair distorts what would normally be a more spherical expansion into this hourglass shape.

  8. Colin J

    Are you sure it’s not the squid? :)

    Fun stuff. I love a parade! and a good mystery!

  9. Celtic_Evolution

    Oh… forgot one other question… are we absolutely sure that what we are observing is in fact a nebula caused by an exploding star? Seems to me that if you know the conditions that should exist for a specific phenomenon, and those conditions do not exist… perhaps you might be misinterpreting the phenomenon… just a thought…

  10. IBY

    PZ is not going to be happy with the squid comment :)

  11. Celtic_Evolution

    @ Andrew

    Hmmm… perhaps… but BA gives two examples of shapes that can be created when stars in a binary go supernova… the first is the “flattened basketball” example, which I like as an explanation for your example: the second star dragging material around its orbit and expanding the sphere in an eliptical shape… but wouldn’t the hourglass shape make more sense if both stars went supernova? Again… I may be improperly assigning behavior here.

  12. amphiox

    If these two stars have stopped hydrogen fusion in their cores, would that still make them A-type main sequence stars? Are they in the process of changing into red giants? How long does that process take? (I was under the impression that this process was quite quick and that one wouldn’t expect to be able to observe stars in this state because of that)

  13. I think it’s the little green men’s version of SETI. They’re trying to talk to us!

    :-)

  14. Kingthorin

    “However, that usually takes a long time, like millions or billions of years. The nebula can’t possibly be that old; such objects are a few thousand years old. ”

    Have we observed and recorded the entire life of a number of nebulae? I don’t believe so. Therefore, how can you make such a statement with any certainty? Doesn’t seem very scientific Phil. Considering we haven’t had telescopes to observe such nebulae for “a few thousand years” (or more) we can hardly assume that we know that they wouldn’t last 100s of thousands of years or longer. Yes we can model the physics and do some math based on what we think we know, but, that’s more of a qualitative conclusion than a quantitative one (since we obviously don’t have a grasp of all the relevant information).

  15. Navneeth

    Regarding possibility #3, shouldn’t it be a rather simple task to find the distance to the stars and check if they belong to the nebula or not?

    P.S.: Why do you use the phrase “the major monkey in the wrench is…,” when the actual phrase is “to throw a monkey wrench into…” (or variations thereof)? I think I remember someone else pointing this out before. :)

  16. Scott Halls

    Like Kesstra said. Maybe the two stars are actually one star, lensed by something else. Now that would be cool.

  17. decius
  18. MarkW

    OK, star-sculpting is some pretty impressive technology, but is it at all possible that it’s an artefact of some ET?

  19. Could it be the heated rantings of the squid heating it up?

  20. Ravenor

    Amphiox: If the two A-type stars have indeed ceased fusing hydrogen in their cores, they would no longer be on the main sequence. They would have evolved off of it and begun an ascent into the red giant phase. :)

  21. Naked Bunny with a Whip

    “we don’t know.”

    We just can’t have nice things, can we? Don’t expect me to buy you a new white dwarf if you can’t be bothered to put it away when you’re done playing with it!

  22. OtherRob

    Navneeth, perhaps Phil was just playing with words a little bit.

  23. Speaking as a person who has not studied the field as deeply as Phil has, and can therefore come to wrong conclusions much quicker – are there cases where nebulae can become brighter over time? Maybe there’s a source directly behind all of it that’s feeding obscuring matter or alternately, is a source of light. Or maybe the answer lies in the overall process of the system rather than the objects themselves.

    @ IBY – On the other hand, PZ might be happy about the squid comment and indeed encourage more squid analogies in astronomy.

  24. infidel
  25. Hannu Siivonen

    “It’s a mystery. I don’t like mysteries! They give me a bellyache, and I’ve got a beauty right now…”

    Is that from the very first episode, “Man Trap”? I just watched it few hours ago, and Kirk said something like that in it.

  26. Torbjörn Larsson, OM

    You implied another possibilty yourself – the squid eated it. Can an astronomer hear stars go “burp”?

    Okay, that is unlikely by slow rotation and equal mass I guess, but that would be my first guess if the listed three possibilities doesn’t add up – somehow the missing star got too close to its sisters.

    @ Kingthorin:

    how can you make such a statement with any certainty?

    As you pontificate on astronomy science instead of simply asking the above, I will assume you are trolling. So instead of touching the trolled bait, instead I ask if you want to bet against that most of the readers actually know how nebulae and white star evolution are dated so it makes your comment totally meaningless?

  27. Why does an exploding star make a ring rather than a sphere?

  28. Navneeth:

    Regarding possibility #3, shouldn’t it be a rather simple task to find the distance to the stars and check if they belong to the nebula or not?

    “Margin of error”?

    At a distance of ~6500 light years, they could easily (in my non-expert opinion) be 30 light years apart and still measure “next to each other”.

  29. Sir Eccles

    I think it is quite clear God did it to test us and there are probably elephants all the way down!

  30. Naked Bunny with a Whip

    ZZMike: It doesn’t. But, like a soap bubble, we can see the edges better because there is “more” material to see, from our point of view.

  31. Jim Shaver

    BA:

    I’m curious about something. In an image like this one, where stars are visible with many different apparent (imaged) diameters, do the diameters in the images correspond in any way to the real diameters of the stars? I realize that when comparing two objects at great distances, a larger apparent diameter doesn’t necessarily mean that one object is bigger than another — it could be that the bigger image is of an object closer to us. But what I really want to know is this: In these images of far away stars, do the diameters in the images represent real sizes of the stars, or are they more like artifacts from an imperfect light-gathering apparatus and process? Do larger diameters in the images really just correspond to brighter objects? Or perhaps are the larger images those of nearer stars that are not in focus?

  32. aiabx

    ZZMike: It doesn’t. But, like a soap bubble, we can see the edges better because there is “more” material to see, from our point of view.

    I had been led to believe that M57 at least is tube shaped, and is so bright and clearly defined because we are looking down the tube. This one could be on odd-shaped one as well.

  33. Kingthorin

    @Torbjörn Larsson, OM
    You can assume anything you want.

    Then you can go ahead and tell everyone you think wants to know (including myself) how astronomers “actually know how nebulae and white star evolution are dated so it makes your comment totally meaningless?”

    After which, I’d still make the argument that if we haven’t observed it and recorded such observations then it’s still our “best guess”. Perhaps such “best guess” or hypothesis (as you may wish to call it) should be good enough but my original question still stands.

  34. Robert

    Just to clarify, since there’s a LOT of confusion:

    Revolve means to orbit something, ie, the Moon revolves around the Earth.

    Rotate means to go around in a circle like a top, ie, the Earth rotates around it’s axis.

    Don’t feel bad if you didn’t know though, the type of handgun known as a “revolver” really should be called a rotator.

    BTW, Phil, what magnitude is the nebula?

    Robert

  35. Dallas

    I read about this story somewhere else and heard the hypothesis that the white dwarf was simply just slung out through gravitational interactions with the two other stars, which, according to them, made sense because the two stars were moving slower than they supposedly should have been.

    As someone who likes to fool around with gravity simulators, it seems like a pretty likely situation. Maybe after sloughing off all those outer layers the friction led the stars to start slowly spiraling toward one another until they became too close and before you know it, bye bye white dwarf.

  36. BILL7718

    Since their rotation around each other is too slow, would that mean they are coming closer together (falling into each other?). Maybe the act of coming together is somehow causing the effect we see.

    Or, maybe the two stars used to be one star.

  37. Sili

    Purdy!

    I guess this doesn’t go with the fact that they rotate too slowly but would it otherwise be possible for one star to ‘eat’ another?

    I know that to conserve angular momentum that would needs must speed up the rotation somewhere, but …

  38. Crux Australis

    What a shame it would be if it were an example of stellar engineering by ETs and we tried so very hard to come up with a natural explanation. Which makes me think…how artificial must an artefact look before we recognise it as an artefact? I guess a star pumping out the prime numbers would be a bit of a gimme, but how simplistic can you get before being mistaken for a natural phenomenon?

  39. Crux Australis

    Maybe an alien species is out there going “Hey stupid Earthlings! See all those rapidly rotating stars you call pulsars? Think that’s natural? That took us millions of alien-hours to create! Hello! Hello?! Anyone there?”

  40. Crux Australis

    Now, a pulsar changing its rotational period to pump out the primes, that would be impressive.

  41. To answer a few questions:

    1) Planetary nebula fade away or expand away in a few thousand years. There are a number of observations to back that claim up. Since this looks just like a PN we assume it’s not terribly old.

    2) The two stars are revolving around each other (orbiting), and also spinning on their own axes. They are spinning slower than would be expected.

    3) They are not main sequence stars, kinda. The observations indicate they are not fusing hydrogen in their cores; they have built up too much helium there. As each star contracts the core heat up, hydrogen starts to fuse in a shell surrounding the core, and the star turns into a red giant. That hasn’t happened yet, but will soon.

    4) It’s very clear from the spectra that these are two separate stars orbiting, not a gravitational lens. Nice guess though!

  42. It’s like hearing a dog barking behind a door, and opening it to see a squid*.

    That would be incredibly cool. Think of the money to be made selling video of a barking land squid.

    Squids are cooler than dogs any day.

    Dogs are, of course, much cooler than cats.

  43. John Hart

    Interaction with dark matter?

  44. Blaidd Drwg

    @ Navneeth: The phrase “Monkey in the wrench” is from the first “Die Hard” movie, when John McClain is talking to the Bad Guy, and tells him he is “The fly in the ointment, the monkey in the wrench”.

    As to the topic, I know it’s a weird question, but is it possible that the material in the ring is flourescing of its own accord? Possibly as a response to the solar energy?

  45. @michael

    For something without prehensile tentacles, that is mighty cool.

    This just arrived for me today: http://tinyurl.com/2fchbz

    It’s nice to see cephalopods getting their due in the plushy market.

    @kingthorin

    IIRC, it’s pretty easy to measure the rate of expansion and calculate when it went off. It’s also easy to observe that, based on expansion rates, they don’t last very long.

    The Crab Nebula (which is not a PN, but still), went off in 1054 (observed and recorded) and is currently about 10 ly in diameter, expanding at about 1800 km/s ( http://tinyurl.com/555ht7 ) Similar techniques for measuring that can be used on PNs to calculate back.

  46. Tom Marking

    “They’re A stars, meaning they’re hotter and brighter than the Sun, but not enough by a long stretch to power the nebula. They simply don’t have what it takes to make the gas so bright.

    Usually, the star in center of a nebula like that is a white dwarf, a compact, dense, hot object leftover when a Sunlike star sheds its mortal coil.”

    Now, I’m confused. The last time I checked the Hertzsprung-Russell diagram the white dwarfs are located in a band which is far below the main sequence by several orders of magnitude. How could a single white dwarf have enough energy to power up the nebula but two near main sequence stars of spectral type A not have enough energy when their combined luminosity is hundreds of times greater than that of a white dwarf?

    http://en.wikipedia.org/wiki/Hertzsprung-Russell_diagram

    Am I missing something?

  47. StevoR

    amphiox on 05 Jun 2008 at 9:19 am


    If these two stars have stopped hydrogen fusion in their cores, would that still make them A-type main sequence stars? Are they in the process of changing into red giants? How long does that process take? (I was under the impression that this process was quite quick and that one wouldnâ??t expect to be able to observe stars in this state because of that)

    & the BA : (& Ravenor replied similarly too.)


    “They are not main sequence stars, kinda. The observations indicate they are not fusing hydrogen in their cores; they have built up too much helium there. As each star contracts the core heat up, hydrogen starts to fuse in a shell surrounding the core, and the star turns into a red giant. That hasnâ??t happened yet, but will soon.”

    So they are sub-giant stars ie. luminosity class IV instead. With the sheer number of stars we do indeed know of many examples of stars inthis stage – probably incl. the 8th brightest star in our sky Procyon (Alpha Canis Minoris), Peacock (Alpha Pavonis), Er Rai (Gamma Cephei), Beta Hydri and the dimmer but larger K type component of Algol (Beta Persei)

    (Sources : James B. Kaler, ‘The 100 Greatest stars’, Copernicus books,2002 & Kaler’s website : http://www.astro.uiuc.edu/~kaler/sow/sowlist.html & Croswell’s online article on Procyon :

  48. Todd W.

    Hmmm…deep space bioluminescing organisms?

  49. @Evolving Squid: “It’s nice to see cephalopods getting their due in the plushy market.”

    Not to mention certain Japanese Motion Picture Genres (No, I’m not talking about cheesy monster movies, either – it’s much worse)

  50. Steven Charles Raine (StevoR)

    D’oh!! Stuffed up a bit there! Clicked wrong button by mistake & sent before intended – then saw I’d got the blockquotes wrong too … My apologies. (Wish I could edit posts here … Sigh.) :-(
    ———————————————————

    So these are sub-giant stars ie. luminosity class IV instead. With the sheer number of stars we do indeed know of many examples of stars in this stage of their lives – incl. the 8th brightest star in our sky Procyon (Alpha Canis Minoris – probably!), Peacock (Alpha Pavonis), Er Rai (Gamma Cephei), Beta Hydri and the dimmer but larger K type component of Algol (Beta Persei).

    (Sources : James B. Kaler, â??The 100 Greatest starsâ??, Copernicus books,2002 & Kalerâ??s website : http://www.astro.uiuc.edu/~kaler/sow/sowlist.html & Croswellâ??s online article on Procyon : http://kencroswell.com/AgeOfProcyon.html )

    Now here’s my thought B type stars tend to be extremely rapidly rotating stars that spin so fast many of them incl. Altair, Achernar and Regulus are flattened with their poles squashed down and their equators bulging out.

    Suppose one such star starts to evolve – & as it does it ejects a whole lot of material forming a nebula as it goes through a long period as a Be shell star (e = emission, shell star =a whole lot of material thrown off forming a shell around the star examples incl. Pleione in the Plieades, Al Hekka or by its Babylonian name Shurnarkabtishashutu I kid you not!) (Zeta Tauri – one of the Horns of the Bull) and Gamma Cassiopeiae.

    So we’ve got a shell of material spreading out from a super-hot, super-fast-spinning Be type star. Now this star runs low on hydrogen and starts to evolve. It cools, swells up – and can’t take the strain of its rotation rate! BANG!

    It splits in twain leaving two roughly equal halves that form a new binary of A type sub-giants – each the same age, the whole system surrounded by a shell of ejected matter resembling a planetary nebula…

    Is this a workable bit of scientific speculation? Maybe? Anyone?

    Of course, there is a problem here in that somehow the A IV or Sirian sub-giant type stars which should be roatating rapidly appear to be rotating slowly instead. I’m not sure what could have caused them to be actually rotating slowly but I do know that there are some cases where we look on apparently slowly rotating stars pole-on so don’t see their actual rotation and are misled by that – Vega is one such case. (See Kaler’s website again for more info on that ..) Perhaps that’s the case here too?

    How sure are we that these stars actually are rotating slowly and we’re not being fooled by the angle we’re seeing them from?

    Well that’s my suggestion although I also consider the speculation reported by Dallas on 05 Jun 2008 at 2:48 pm to be quite likely :
    “I read about this story somewhere else and heard the hypothesis that the white dwarf was simply just slung out through gravitational interactions with the two other stars, which, according to them, made sense because the two stars were moving slower than they supposedly should have been.”

    Now if that was the case I’d imagine a search could be conducted to find any nearby white dwarf that could be traced back to the nebula at the right time – this should be possible shouldn’t it? Has that be tried already or not?

    Whatever the answer – a great mystery and post BA You’ve got me really intrigued and thinking. Thanks! 8)
    Anyway an

    that the ejected wjite dwraf in a binary one

  51. Evolving Squid said

    Dogs are, of course, much cooler than cats.

    Uh oh. Forget Republican v Democrat, religion v atheism, country v western… them’s is fightin’ words.

    Dogs smell. Cats are cleaner. Cats rule dogs drool.*

    *I actually like dogs too but Copernicus is watchin’.

  52. Well you’ve cleared up on misconception I had BA I thought that at least some nebula glowed because they were like plasma or something – they glowed because they were still warm enough to glow. But if something external actually ionises the gases then… What about dark energy?

  53. StevoR

    # Sili on 05 Jun 2008 at 4:19 pm

    Purdy! I guess this doesn’t go with the fact that they rotate too slowly but would it otherwise be possible for one star to ‘eat’ another? I know that to conserve angular momentum that would needs must speed up the rotation somewhere, but …

    Yes, some stars can fuse together and merge into one – this is the ultimate fate of contact binaries like W Ursae Majoris (prototype example), 44 Bootis B (nearest example 38 ly off) & ER Vulpeculae (a.k.a. Hd 200391 – 2 very sun-like stars – & see Ken Croswell’s article : “Dance of the Double Sun”, in ‘Astronomy’ magazine, July 1993, Kalmbach publishing Co.) which end up as single fast-spinning fused stars like FK Comae Berenices – one such star that has been identified & is the prototype of its class.

    However, if the white dwarf had merged with the binary, I’d think signs of that should be evident in the system – one of the stars should have spun up & be highly star-spotted – or more likely perhaps have gone supernova (type Ia) when the white dwarf absorbed too much material and exploded in the process!

    Of course, if the stars really are rotating super-rapidly & we’re just not seeing that from our viewpoint then that could be right stilll .. maybe? (Plus, there’s also the possible tidal locking factor to consider as a slowing mechanism but I don’t think they’re close enough or old enough for this to have happened are they?)

    Asked Tom Marking on 05 Jun 2008 at 9:36 pm
    “They’re A stars, meaning they’re hotter and brighter than the Sun, but not enough by a long stretch to power the nebula. They simply don’t have what it takes to make the gas so bright.

    Usually, the star in center of a nebula like that is a white dwarf, a compact, dense, hot object leftover when a Sunlike star sheds its mortal coil.”

    Now, I’m confused. The last time I checked the Hertzsprung-Russell diagram the white dwarfs are located in a band which is far below the main sequence by several orders of magnitude. How could a single white dwarf have enough energy to power up the nebula but two near main sequence stars of spectral type A not have enough energy when their combined luminosity is hundreds of times greater than that of a white dwarf?

    … Am I missing something?

    Sorry Tom, but, yes, I’m afraid you are : Temperature & wavelength emitted is what I think you’re missing.

    White dwarfs are the exposed cores of stars and thus are – at least in the beginning – staggeringly, unfathomably hot objects. For example, our Sun has a surface temperature of 5,800 degrees Kelvin but a core of nearly 16 million degrees Kelvin. When a star sheds its outer layers to first expose itscore thecore is the hottest object it can possibly be and emits its energy mainly in the form of UV rays which ionise those outer layers as a planetary neb. Its visual light maybe fairly dim given its small size but in UV and X-rays its pretty bright.

    For example – & I’m looking at a dramatic photographic illustration of this now taken from the Chandra X-ray observatory (Page 172, Kaler, ‘100 Greatest Stars, 2002) – the Pup, (the white dwarf Sirius B), is lost in the glare of the Dogstar (Sirius A) visually but, at X-ray wavelengths the situation is reversed with the Pup being much, much brighter than its A-type white main sequence companion!

    (Ironically, both Sirius’s Dogstar & Pup could really be called “white dwarfs” because ‘dwarf’ means main-sequence star and A-type stars are white! (A la Blue dwarf, yellow dwarf, orange dwarf, red dwarf, etc ..) Yet, of course, a white dwarf is actually something very different and, indeed, is not really a star but essentially a star’s corpse! For that reason, I use the term ‘Sirian’ to describe A-type dwarfs – & Procyonese for the yellow-white F-type dwarfs too!)

    # Kingthorin on 05 Jun 2008 at 9:28 am
    “However, that usually takes a long time, like millions or billions of years. The nebula can’t possibly be that old; such objects are a few thousand years old. ”

    Have we observed and recorded the entire life of a number of nebulae?

    You’re sounding a lot like a troll but, what the heck, I’ll answer that anyway :

    What we’ve observed is hundreds – indeed thousands – of planetary nebulae – and their precursors protoplanetary nebuale and dust shrouded Mira type stars – at various stages of their lives.

    Its like this, you look at a crowd at a big family meeting, there’ll be babies, toddlers, little kids and teenagers, adults and elderly people there. Now you don’t have time to watch one grow to the next stage but you do have a representative sample of people over a wide range of ages there and by examination you can tell how a human lifecyle goes. Similarly we see stars in all stages of life, youthful suns like T-Tauri, older stars like our Sun, stars getting older like Procyon*, elderly stars like Arcturus, dying stars like Mira* and dead stars like white dwarfs such as Sirius B (aka “the Pup”!), Van Maanen’s Star and the central stars of planetary nebulae.

    So yes, we do know and understand the stellar life cyle incl. the planetary nebula stage that stars like our sun go through pretty well.

    ——————————
    * Mira and Procyon interesting enough, have exactly the same mass : 1.5 x solar mass. Thus we know today’s Procyon is tommorrows Mira & vice-versa! ;-)

  54. StevoR

    BILL7718 on 05 Jun 2008 at 3:07 pm :

    “Since their rotation around each other is too slow, would that mean they are coming closer together (falling into each other?). Maybe the act of coming together is somehow causing the effect we see.

    Or, maybe the two stars used to be one star.”

    That last line sums up my theory in a line.

    Good thing is that we can possibly work out from the nebula and the binary just what sort of star it would’ve been beforehand.

    For example, A type Sirian dwarf stars range from 2 to 4 solar masses so if each of the binary stars is, say, 3 solar masses we can tell the original star was a 6 mass Be shell star. (exact spectral class B2e, B3e something like that?) Plus add in whatever material was ejected into the surrounding nebular shell – say, another solar mass, (?) to make the original star a 7 solar mass blue dwarf at birth. Maybe …?

    (B stars range from 4 [B9]to 20 [B0] solar masses, above that are only O type stars – the most extreme class in mass, heat, blueness, shortness of lifespan, etc ..for normal, main-sequence stars.)

    Additionally, from the fact it was rotating fast enough to split apart we can calculate roughly what speed it was rotating at & so on … Cool! 8)

    Then again, that’s assuming this scenario turns out to be the case … which may not be. I really hope it is coz that’d be just superluminous
    but, yes, I could well be wrong. :-(

    Could there be some sort of evidence for or against this idea in the nature of the nebula and central binary? I’d expect so but I don’t know for sure …? BA ? Anyone?

  55. StevoR

    Suggested shane on 05 Jun 2008 at 11:27 pm :


    “Well you’ve cleared up on misconception I had BA I thought that at least some nebula glowed because they were like plasma or something – they glowed because they were still warm enough to glow. But if something external actually ionises the gases then… What about dark energy?”

    Nice thought but, alas, dark energy is dark because it doesn’t interact with normal (baryonic) matter except gravitationally so that’s unlikely …

    Incidentally, the Mira-Procyon similarity noted goes further than mass -both share white dwarf companions too & eventually both will become white dwarf binaries … Mind you Procyon A (“the little dogstar”) must be just a fraction less massive than Mira was because Mira A (Omicron Ceti) has lost some mass already to get down to its current 1.5 solar masses; for example in the “comet-like” tail of material its shed ..(visually-InfraRed? Spotted the other year via Spitzer if I’m recalling right?)

    PS. Sorry, not meaning to hog this debate but trying to inform and entertain a little here too .. This is my last post here for tonight! [6pm in Oz] promise!
    ——–
    Argh! typos & lack of bits that should be in blockquotes & italics (ie.Tom Markings post being quoted) actually being in those, ad nauseam .. Oh how I wish I could edit these posts! :-(

  56. Kingthorin

    @StevoR

    Thank you for the explanation. It brings us somewhat closer. However using your family reunion example what about dwarfism? Having been to a family reunion and spent a number of years in the world I would assume I have an understanding of how these human things (compare nebulae) evolve and I’d likely be pretty good at “guessing” people’s ages. Then I meet a dwarf who is only 3′ tall, I assume this must be a child however I later learn they’re 55. We’re even talking similar scales here, we’ve observed thousands of nebulae (or so you and others have said here) I’ve observed thousands of humans. Out of the billions available there was something I hadn’t seen.
    Saying “The nebula can’t possibly be that old; such objects are a few thousand years old.” is like saying “that 3′ tall person can’t possibly be 55, when people are 3′ tall they’re only children”.

    @ Evolving Squid
    Thanks for the examples.

    —–

    I apologize for upsetting people. In reality I think Phil is a great guy and find this blog a great read. This post and the assumptions therein just didn’t seem very scientific. To say something can’t be just because we haven’t observed it yet seems very much counter to so many other things we talk about around here.

  57. Nigel Depledge

    Kingthorin said:
    I apologize for upsetting people. In reality I think Phil is a great guy and find this blog a great read. This post and the assumptions therein just didn’t seem very scientific. To say something can’t be just because we haven’t observed it yet seems very much counter to so many other things we talk about around here.

    Although Phil did not explicate how we know that planetary nebulae are merely thousands of years old (as opposed to millions), there is a lot of data and some very strong reasoning behind this “assumption”. After a little thought, I am sure you will see that your initial objections were a bit naive.

    We have observed many planetary nebulae. Planetary nebulae expand. We can measure their rate of expansion, and their present size. Ergo, we can determine their ages (in fact, we can determine a maximum age for a PN, because the expansion slows as the ejecta from the star slam into the existing intertellar medium. The expansion was faster in the past, but we don’t know by how much. Therefore, ages determined for PNs are always maximum ages). Since we have observed many PNs, and none of them is older than perhaps 10-20 thousand years, we can draw a strong conclusion.

    If PNs lasted millions of years, we should have seen more PNs older than 100,000 years than PNs younger than 100,000 years (if it lasts 1 million years, then only 10% of the ones we observe should be less than 100,000 years old, assuming a random distribution and a representative sample). Since we do not observe any really old PNs, we can quite reliably conclude that, after a few thousand years (or perhaps a few tens of thousands of years), they fade away, to a point where they are no longer ionised and therefore no longer emit the light by which we detect them.

    Additionally, we can make calculations based on our knowledge of stellar evolution, to determine how much UV the star emits and over what distance it can ionise the material it sloughed off earlier. If this correlates with our observed ages for PNs, this correlation strengthens both our confidence in our knowledge of stellar evolution and our confidence in the ages of the PNs.

    You see?

  58. Kingthorin

    “You see?”

    Yes I see we can make calculations and assumptions that a dwarf can’t exist before having seen a dwarf.

    My point is simply: Yes we can state it with high confidence but we shouldn’t state it as fact (as it was in the blog post).

    “The nebula can’t possibly be that old; such objects are a few thousand years old.” Seems an awful lot like statement of fact.

    “Based on what we’ve observed to-date the nebula likely isn’t that old; so far we’ve only observed such objects as thousands of years old.” Or something along those lines would have been much better.

  59. The Barber of Civility

    It looks a lot like Green Lantern’s ring, so maybe the nebula is powered by the sun around Oa. Or it could be one of those new, superbright LEDs you can buy online. They’re so small that you can put them in a ring (with the battery). That would be really hard to detect at this distance.

  60. Torbjörn Larsson, OM

    @ Kingthorin

    …assume anything you want … I’d still make the argument …

    It is no longer an assumption, it is now a validated prediction.

    See? Science. It works, bitches.

  61. Torbjörn Larsson, OM

    I read about this story somewhere else and heard the hypothesis that the white dwarf was simply just slung out through gravitational interactions with the two other stars

    Ah, should have realized it from my own attempt of analysis.

    Don’t feel bad if you didn’t know though, the type of handgun known as a “revolver” really should be called a rotator.

    Ah, but you are thinking of the passive magazine. (Passive as regards loading action, or hitting the target, more main concerns of the operator.) Besides, “revolver” might be a faster, more reliable heuristics to keep tabs on the remaining bullets. It is also distinct from a symmetrical rotator gun such as a Gatling gun, which is constantly fed.

    But actually I suspect “revolver” just sounds better than “rotator”.

  62. Torbjörn Larsson, OM

    @ Kingthorin:

    I have now read remaining arguments, and I will revoke my offered bet since enough peoples have confirmed to you that they in fact know how nebulae are dated.

    My point is simply: Yes we can state it with high confidence but we shouldn’t state it as fact (as it was in the blog post).

    “The nebula can’t possibly be that old; such objects are a few thousand years old.” Seems an awful lot like statement of fact.

    Okay, this is still pontificating, but looks more like an honest misunderstanding.

    Empirical science is all about observational facts and validated theories – such “validated beliefs” are all knowledge. Of course it is revisable knowledge, observations can be wrong and theories incomplete. However, as repetitions and tests builds up this gets highly unlikely.

    In fact a theory that is validated by passing a number of tests on its predictions is more solid than an isolated observational fact. And as a theory owns its facts, it is one huge meta fact.

    In addition, observed processes are facts too. You know for a fact that you age, and astronomers knows for a fact that nebulae expand. You know for a fact that you can’t be older than a few 10s of decades, and astronomers knows for a fact that nebulae can’t be older than a few thousand years.

    So expanding nebula are both fact and theory, and any conclusions that can be entirely deducted from verified characteristics are also facts.

    “Based on what we’ve observed to-date the nebula likely isn’t that old; so far we’ve only observed such objects as thousands of years old.” Or something along those lines would have been much better.

    That would be a cautious way to formulate facts (perhaps overly cautious, but I’m no astronomer), but it would still be facts. Scientists express themselves this way all the time, all the while being aware that in many cases this is facts.

    That depends on how quantifiable and large those likelihoods are. As I described above, after a while those likelihoods passes from “verified beyond reasonable doubt” (i.e. fact), which can be exactly quantified, to “impossible to be falsified” (i.e. “I can bet my house on this” fact), which can be roughly qualified.

    It is for instance impossible that electrons doesn’t exist, despite that we don’t observe them directly. [Takes a look on the screen. Still taking input. Well then.]

  63. Torbjörn Larsson, OM

    Errata: change “cautious” to precise, and “observe them directly” to observe them directly in our daily life. (The difference between science and popular sense of direct observation is another subject for a long comment, so I’ll skip that one.)

  64. @Tom
    How could a single white dwarf have enough energy to power up the nebula but two near main sequence stars of spectral type A not have enough energy when their combined luminosity is hundreds of times greater than that of a white dwarf?

    WDs radiate a lot of UV. Class A stars radiate primarily visible. UV makes the gas glow, visible light does not. The same basic reason that a fluorescent tube lights up with a little bit of electricity (which creates UV with the gas in the tube), but exposing it to sunlight doesn’t do anything for it.

    @shane
    Dogs smell. Cats are cleaner.

    To my nose, cats have a foul aroma on par with skunks. Nevertheless, they are no cleaner, they’re just covered with cat spit instead of regular yard dirt.

    In any case, cephalopods are way cooler than either :)

  65. rcglinsk

    Perhaps this nebula is a normal nebula and the 1987A supernova is a normal supernova. They’re both very close by and a lot easier to study than any nebula that has a neutron star in it for example. Our ideas about far away nebulas are based on much less direct observations. Could it be that star death can leave behind something other than a white dwarf? That a supernova can leave no star behind? Perhaps those outcomes are ordinary and we’ve been misinterpreting the data from the far away events.

  66. Tom Marking

    “Sorry Tom, but, yes, Iâ??m afraid you are : Temperature & wavelength emitted is what I think youâ??re missing.

    White dwarfs are the exposed cores of stars and thus are – at least in the beginning – staggeringly, unfathomably hot objects.”

    “WDs radiate a lot of UV. Class A stars radiate primarily visible.”

    As usual when I’m struggling with a problem like this, I went off and wrote a program to calculate this. Assuming both main sequence stars and white dwarfs adhere to the blackbody radiation formula:

    http://en.wikipedia.org/wiki/Planck%27s_law

    I(LAMBDA,T) = (2*H*C^2 / LAMBDA^5) / (exp(H*C/(LAMBDA*K*T)) – 1)

    It’s not too hard to integrate this formula over a range of wavelengths. Using data from Wikipedia for Sirius A and Sirius B (a white dwarf):

    http://en.wikipedia.org/wiki/Sirius

    And using the following ranges:
    Visible light: 380 – 750 nanometer wavelengths
    Ultraviolet light: less than 380 nanometer wavelengths
    Infrared radiation: greater than 750 nanometer wavelengths

    I integrated the formula from 1 nanometer out to 20,000 nanometers using a step of 1 nanometer.

    I came up with the following results:

    Star: Sirius A
    Spectral Type: A1V (main sequence star)
    Luminosity of the star = 25.4 suns
    Surface temperature of the star = 9940.0 deg K
    Total power per unit area = 5.535E8 watts per square meter
    Radius of the star = 1.703 solar radii
    Visible light = 9.989 suns (39.3%)
    Ultraviolet = 11.150 suns (43.9%)
    Infrared = 4.262 suns (16.8%)

    Star: Sirius B (white dwarf)
    Spectral Type: DA2
    Luminosity of the star = 0.026 suns
    Surface temperature of the star = 25200.0 deg K
    Total power per unit area = 2.287E10 watts per square meter
    Radius of the star = 0.008 solar radii
    Visible light = 0.002 suns (7.8%)
    Ultraviolet = 0.024 suns (90.5%)
    Infrared = 0.0004 suns (1.7%)

    Thus, it is indeed true that the white dwarf is radiating 90 percent of its power in the ultraviolet and X-ray region whereas the main sequence star is only radiating 44 percent of its power in the ultraviolet/X-ray region. However the UV power from Sirius A is 465 times the UV power of Sirius B. With such a small total luminosity of the white dwarf even a modest percentage of the parent’s star energy going into UV is enough to dwarf (no pun intended) the UV output of the white dwarf. Thus, if the white dwarf’s UV radiation is enough to power up the nebular gasses then the UV radiation from two A class stars is more than enough to do it. My objection still stands.

  67. StevoR

    Tom Marking

    Neat work there & good calculations. I’m impressed. 8)

    However, I still don’t agree with your “objection still standing.” I know that its been long established and aknowledged that only the most massive and hottest stars of types O & early B and the youngest, hottest white dwarfs emit enough UV to ionise planetary nebulae -or for that matter other nebulae. (eg. Rigel ionises the Witch Head nebula – IC 2118.)

    Don’t forget that Sirius B is an old white dwarf which has cooled down with age and was originally much brighter – in UV, X-ray and other high end wavelengths. That’s one reason why the Pup now no longer illuminates the planetary nebula that was once around the Dogstar! ;-)

    It might also be worth noting that I’m not sure you’ve included all the radiation emitted by Sirius B over all wavelengths incl. X-ray gamma-ray etc … But as I said before I’m impressed! :-D

    Kingthorin Fair enough – I see what you’re getting at & accept you’re no troll although you at first did sound a bit too much like some we get here. Sorry.

    It’s the anomalies that make science so intriguing &, no, we don’t understand everything perfectly yet but we do work hard to figure them out – and throwing out well established things like the age of planetaries is a last resort adopted only when no other conclusion at all is possible.

    This sure is an odd one but I’m confident we’ll figure out what’s happening here eventually. I reckon my idea or the one mentioned by Dallas are still the most likely answers but I’ll admit I’m not sure.

    Thanks for the links Sergei!

    —————————————

    “The blue supergiant star Rigel A emits more light in a minute than the Sun does in a month and is the most radiant star within a 1,000 light year radius from the Sun.”
    – Ken Croswell, “The Blue Witch” in ‘Sky &Telescope’ magazine May-June 2007.

  68. Kingthorin

    @StevoR

    Thanks I appreciate that!

  69. Tom Marking

    Here is some data for main sequence stars:

    Spectral type and luminosity class = O5V
    Type of star = blue dwarf (main sequence)
    Luminosity of the star = 1.46E4 suns
    Surface temperature of the star = 32,500 deg K
    Absolute magnitude of the star = -5.6
    Mass of the star = 1.55E1 solar masses
    Total lifetime of the star = 1.06E7 years
    Total power per unit area = 6.33E10 watts per square meter
    Wavelength of peak radiation = 89 nanometers
    Radius of the star = 3.84E0 solar radii
    Visible light = 6.22E2 suns (4.27%)
    Ultraviolet = 1.38E4 suns (94.89%)
    Infrared = 1.22E2 suns (0.84%)

    Spectral type and luminosity class = B5V
    Type of star = blue dwarf (main sequence)
    Luminosity of the star = 1.94E2 suns
    Surface temperature of the star = 18,000 deg K
    Absolute magnitude of the star = -0.9
    Mass of the star = 4.51E0 solar masses
    Total lifetime of the star = 2.32E8 years
    Total power per unit area = 5.95E9 watts per square meter
    Wavelength of peak radiation = 161 nanometers
    Radius of the star = 1.45E0 solar radii
    Visible light = 3.12E1 suns (16.06%)
    Ultraviolet = 1.55E2 suns (79.86%)
    Infrared = 7.92E0 suns (4.08%)

    Spectral type and luminosity class = A5V
    Type of star = blue-white dwarf (main sequence)
    Luminosity of the star = 1.22E1 suns
    Surface temperature of the star = 9,250 deg K
    Absolute magnitude of the star = 2.1
    Mass of the star = 2.05E0 solar masses
    Total lifetime of the star = 1.67E9 years
    Total power per unit area = 4.15E8 watts per square meter
    Wavelength of peak radiation = 313 nanometers
    Radius of the star = 1.38E0 solar radii
    Visible light = 5.12E0 suns (41.84%)
    Ultraviolet = 4.73E0 suns (38.61%)
    Infrared = 2.39E0 suns (19.56%)

    Spectral type and luminosity class = F5V
    Type of star = white main sequence star
    Luminosity of the star = 2.81E0 suns
    Surface temperature of the star = 6,750 deg K
    Absolute magnitude of the star = 3.7
    Mass of the star = 1.34E0 solar masses
    Total lifetime of the star = 4.79E9 years
    Total power per unit area = 1.18E8 watts per square meter
    Wavelength of peak radiation = 429 nanometers
    Radius of the star = 1.24E0 solar radii
    Visible light = 1.31E0 suns (46.61%)
    Ultraviolet = 4.92E-1 suns (17.55%)
    Infrared = 1.01E0 suns (35.85%)

    Spectral type and luminosity class = G2V
    Type of star = yellow dwarf (main sequence)
    Luminosity of the star = 1.00E0 suns
    Surface temperature of the star = 5,800 deg K
    Absolute magnitude of the star = 4.8
    Mass of the star = 1.00E0 solar masses
    Total lifetime of the star = 1.00E10 years
    Total power per unit area = 6.42E7 watts per square meter
    Wavelength of peak radiation = 500 nanometers
    Radius of the star = 1.00E0 solar radii
    Visible light = 4.39E-1 suns (43.92%)
    Ultraviolet = 1.02E-1 suns (10.16%)
    Infrared = 4.59E-1 suns (45.91%)

    Spectral type and luminosity class = G5V
    Type of star = yellow dwarf (main sequence)
    Luminosity of the star = 6.43E-1 suns
    Surface temperature of the star = 5,500 deg K
    Absolute magnitude of the star = 5.3
    Mass of the star = 8.81E-1 solar masses
    Total lifetime of the star = 1.37E10 years
    Total power per unit area = 5.19E7 watts per square meter
    Wavelength of peak radiation = 527 nanometers
    Radius of the star = 8.92E-1 solar radii
    Visible light = 2.71E-1 suns (42.18%)
    Ultraviolet = 5.23E-2 suns (8.14%)
    Infrared = 3.19E-1 suns (49.68%)

    Spectral type and luminosity class = K5V
    Type of star = orange dwarf (main sequence)
    Luminosity of the star = 5.23E-2 suns
    Surface temperature of the star = 4,250 deg K
    Absolute magnitude of the star = 8.0
    Mass of the star = 4.30E-1 solar masses
    Total lifetime of the star = 8.23E10 years
    Total power per unit area = 1.85E7 watts per square meter
    Wavelength of peak radiation = 682 nanometers
    Radius of the star = 4.26E-1 solar radii
    Visible light = 1.54E-2 suns (29.45%)
    Ultraviolet = 1.09E-3 suns (2.09%)
    Infrared = 3.58E-2 suns (68.46%)

    Spectral type and luminosity class = M5V
    Type of star = red dwarf (main sequence)
    Luminosity of the star = 6.63E-4 suns
    Surface temperature of the star = 3,250 deg K
    Absolute magnitude of the star = 12.8
    Mass of the star = 1.24E-1 solar masses
    Total lifetime of the star = 1.86E12 years
    Total power per unit area = 6.33E6 watts per square meter
    Wavelength of peak radiation = 892 nanometers
    Radius of the star = 8.20E-2 solar radii
    Visible light = 9.63E-5 suns (14.54%)
    Ultraviolet = 1.84E-6 suns (0.28%)
    Infrared = 5.65E-4 suns (85.18%)

  70. StevoR

    to Kingthorin : No worries! :-)

    To Tom Marking Thanks!
    __________________________________

    Hmm .. This must be a record as far as late posts go .. but still I just thought I’d just say! ;-)

    BA In the unlikely event you read this – Please can you update us on what the deal is & please tell us what you think of my conjectured solution here?

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