The Wonderful

By Phil Plait | August 15, 2007 11:32 am

The image above is substantially cool. But it’ll take a moment to explain why. Stick with this; you’ll like it.

In the constellation of Cetus, the whale, is what appears to be a run of the mill red star. At a distance of about 400 light years, the fact that you can see it with your unaided eye at all means it’s an intrinsically luminous star: at that distance the Sun would be completely invisible.

The star is a red giant, a star that was once much like the Sun but is now terminally ill. Stars make energy in their core through the fusion of light elements into heavier ones; the Sun is currently fusing hydrogen into helium. Eventually it will run out of hydrogen, and will begin to fuse helium into carbon and oxygen. In 7 billion years or so the helium in the core will run out as well. The carbon and oxygen ash from the process will form a ball about the size of the Earth. It will contract and get incredibly hot. Helium outside the core, previously unavailable for fusion (like having a spare can of gasoline in the trunk of your car) will start to fuse in a thin shell surrounding the core. This will dump vast amounts of heat into the outer part of the Sun, which will respond like any gas will when heated: it will expand and cool.

The Sun will become a red giant. But thin shell helium fusion is unstable, and so a red giant can expand and contract, sometimes almost in a spasm, ejecting material off its surface, and briefly becoming very luminous before settling down again. This will happen three or four times for the Sun, and it will totally eject its outer layers, exposing the hot core to space*. When this is all done, the Sun will be a white dwarf, and will slowly cool for the next few hundred billion years.

The image at the top shows a star that is undergoing this process right now. Called Mira — "wonderful" — it’s slightly more massive than the Sun, and far older. It has only a short time left — maybe only hundreds of thousands of years, maybe less — before its paroxysms slough off that last bit of outer layer, and it becomes a white dwarf. These spasms change its luminosity, and we see this as a brightening and dimming of the star; it’s sometimes too faint to see with the unaided eye, and other times can brighten considerably.

Mira has long been studied by astronomers to give us insight on what will happen when the Sun dies. Observations have revealed the star isn’t round: that makes sense, since it is ejecting huge amounts of material in expanding clouds. It has a small companion, a more normal star that appears to be collecting some of the ejected material and forming it into a disk around itself.

Mira is definitely wonderful, in the sense of evoking wonder. And now we have found out it’s even more amazing than we thought. Most stars near the Sun orbit the center of the Galaxy at roughly the same speed, but some are faster than others. Mira, it so happens, is plowing through this local region of space at about 130 kilometers per second (about 80 miles per second). There is gas and dust out there, a thin haze floating among the stars. As Mira screams through this fog, the gas it is ejecting as it convulses is blown backwards, leaving a long tail behind it — imagine running down the street with a smoke bomb in your hand and you’ll get the idea.

Now take another look at the image at the top of this page. Mira is on the right hand side, and is moving left to right. The long tail of ejected material is incredible — it’s 13 light years long! It has taken Mira 30,000 years to move this distance, which means that the material in the left hand side of the tail was ejected 30 millennia ago. If you look at the location of the star itself, you’ll see a parabolic arc in front of it; that’s the bow shock, where Mira’s ejected material is slamming into the material between stars (called the interstellar medium or ISM).

The images are in the ultraviolet, which means the gas is emitting UV radiation. This indicates that the material is being heated by the collision with the ISM, and is slowly losing that energy by glowing in the UV. The images were taken by the Galaxy Explorer (GalEx) mission. In a routine survey, an astronomer noticed that Mira looked fuzzy, so they took deeper images. The tail near the star was revealed, so they scheduled even more observations to trace it out… I can just imagine how surprised they were when they realized what they had found! The image is actually a mosaic of the images GalEx took.

The material blown off will eventually merge with the ISM and form new stars. The elements created in the fusion forge deep inside of Mira will eventually find themselves in new stars, some of which will be like the Sun, or like Mira once was. They too will age, step through the fusion process in their cores, and eventually become red giants… and the cycle starts again. It’s quite possible that some of the heavier elements we see in the Sun itself were seeded into the Galaxy by some anonymous star like Mira more than 5 billion years ago.

So when you look at this image of Mira with its comet-like tail, think on this: you are seeing a star’s way of making new stars. Like life itself, in death is renewal and the foundation for future generations.

*Needless to say, the Earth doesn’t fare well in all this.

CATEGORIZED UNDER: Astronomy, NASA, Pretty pictures

Comments (71)

  1. Arthur Maruyama

    Wow. Just wow.

    Thanks, BA, for bringing this to your readers’ attention AND the description. And, yes, I did like it.

  2. “The Sun will become a red giant. But thin shell helium fusion is unstable, and so a red giant can expand and contract, sometimes almost in a spasm, ejecting material off its surface, and briefly becoming very luminous before settling down again. This will happen three or four times for the Sun, and it will totally eject its outer layers, exposing the hot core to space*. When this is all done, the Sun will be a white dwarf, and will slowly cool for the next few hundred billion years.”

    I have always wondered about this: How long does the expansion to Red Giant actually take? Minutes? Years?

    And roughly how long between the three or four spasmodic ejections, and then roughly how long does the shrinking to white dwarf take? Weeks? Or years? I’ve never been able to grok the scale of time involved…

    Thank you,

    Jonathan

  3. Dan

    Hey! I just got an idea for my next Fourth of July fireworks display. That’ll make the neighbors go “Ooo…”

  4. WJM

    This stuff wasn’t known about Mira before?

    Wow.

    Wonder and wonderful, indeed. I love you star-talkin’ guys.

  5. DrFlimmer

    Mira, indeed!

    @Jonathan:
    Well, it does not change from one second to another. When a star is running out of fuel (hydrogen) it does not start fusion of helium at fixed point in time. It’s a slow process where one part is becoming more important and the other one (fusion of hydrogen) is becoming less important. And so more and more oxygen and carbon is fusioned over a long period of time and settles down to the inner core of the star.
    You see, and I guess you knew it allready, this all takes a long time and slowly the star becomes a red giant and grows like Phil explained above.
    Sometimes the luminosity of a red giant increases rapidly, in days. The fading then needs maybe weeks. That is also pretty fast in astronomy.
    “Becoming a red giant” is, as mentioned, a very long process taking millions of years. Also the white dwarf needs a long time to “be built” because this is also not a fixed point.
    This is not a supernova… that would be really fast. In a supernove a star explodes in seconds.

    Maybe we can conclude: Most things in astronomy happen very very slowly taking millions of years. Some things are faster, and few things are very fast!

    Maybe this helped you a bit (sorry for bad english maybe, I am trying as hard as I can to become better ;) )

  6. lizzyshoe

    That’s fantastic! I think Mira just became my new favorite star. Did anyone read that Discover magazine article on how Mira darkens because of the titanium oxide it produces? This is so cool. Can’t wait for the next set of images.

  7. Glenn

    Awe-inspiring, Phil. Thank you!

    It has a small companion, a more normal star that appears to be collecting some of the ejected material and forming it into a disk around itself.

    Is the companion and/or its disk visible in the images? In the “close-up,” I see a couple of bright spots right behind (to the left of) what I think is Mira itself. Is the rounder, smaller spot the companion star, by any chance?

  8. John

    Awesome as always, thanks Phil.

    Like Lizzy, I think I have a new favorite star. :D

  9. Rook

    Seeing this warms the mind….

    thanks Phil!

  10. Navneeth

    Wonderful image and nice summary. Just before I came to your article, I saw the photo at space.com and went :O :O :O.

    I hope this makes to your list of top 10 astro images for this year. :)

  11. Chip Gentry

    The “tail” seems to have a little bit of curvature. I wonder if that is real or perspective in some way?

    Chip Gentry

  12. PK

    At 400 light years from here, Mira is fairly close by in the milky way (which is roughly 100 000 light years across). Assuming that it is roughly the same distance from the center of the milky way, the curvature of Mira’s orbit as perceived by us will be considerable. I don’t know how this tail is oriented in the sky, but I wouldn’t be surprised if the curvature is due to this.

  13. Amstrad

    Why doesn’t the blown off material travel along with the proper motion of the star? Is is drag caused by ISM?

  14. Gnat

    Question: What does the companion star do with the collected material? It’s forming a disk, but what does that mean for the companion star?

    Okay that was two!

    :)
    Gnat

  15. Eric

    I have two questions about this whole process that have been on my mind for a while –

    If stars fuse hydrogen to helium to oxygen and carbon and eventually hit a road block at iron,

    1) Where does fresh hydrogen for new stars come from if it is constantly being turned into heavier elements? will the supply of hydrogen ever end?

    2) If there is a road block at iron, how do we get heavier elements?

  16. Glenn

    Most stars near the Sun orbit the center of the Galaxy at roughly the same speed, but some are faster than others. Mira, it so happens, is plowing through this local region of space at about 130 kilometers per second (about 80 miles per second).

    More n00b questions:
       • How can two nearby stars orbit the
    center of
         the galaxy at significantly different speeds?
       • Are the faster ones moving outward as well
         and/or the slower ones spiraling inward?
       • If so, will the former eventually escape the galaxy and
          the latter eventually get sucked into the central black hole?

    Again, thank you, Phil!

  17. Patrick

    This is really cool news…

    I have a question though. You say that most stars are moving about the same speed around the galaxy. According to wikipedia, the sun moves about 217 km/s, so a good bit faster than Mira.

    Am I looking at the wrong numbers, or is WP wrong here (the source seems reliable)?

    Or is Mira’s collision with the ISM slowing her down?

  18. Patrick

    @Eric

    To answer your second question, heavier elements can be formed during supernovas. Look up Supernova nucleosynthesis on wikipedia.

  19. Ken G

    The description makes it sound like there’s carbon and oxygen (“heavier elements”) in that wake, but I was under the impression that lower-mass stars (like Mira and our Sun) pretty much keep their carbon and oxygen to themselves. If so, then you actually need supernovae to get the “heavier elements” out into the new stars– all you get from Mira and our Sun is the hydrogen and helium that you more or less started with. Also, the process is so slow that many many generations of massive stars have gone supernova in the time it took Mira to get to this point. So I agree the picture is gorgeous, and the explanation is poetic, but I think the impact on new star formation is oversold– let’s give the massive stars, and supernovae, their due on that score, unless my understanding is wrong!

  20. Mike C

    Thanks for a great post, Phil. This is the reason I come to this site.

  21. ioresult

    Patrick, I was about to post about the speed also. I guess the 130km/s speed is the speed with respect to the interstellar medium, wich I suppose is also roughly orbiting the center of the galaxy. So that would mean Mira could be going at a different speed than most other start, in a different direction, or any combination of the previous.

  22. Leon

    Pretty impressive!

    I’m curious–how long will it be before the Sun converts to helium burning, and what will happen to the inner planets? Is there little to no effect? Does the amount of solar radiation change much?

  23. Tim G

    Happy trails, Mira!

    The interstellar medium varies greatly in density so I take it that in some regions of the galaxy the bow shock would be far more substantial than in other regions.

  24. DrFlimmer

    @Eric

    Your second question is allready answered, so here is a try for your first:
    Well, all hydrogen was made in the Big Bang. There is no possibility to make new. But not all the hydrogen is in the stars allready. It is nearly everywhere in clouds or some sort of that. Those clouds can be hit by a shockwave (like the one of Mira) which maybe consits heavier elements and then the cloud maybe starts collapsing and building up a new star and even planets.
    Our sun is rather new. And her “cloud” must have been hit by such a shockwave of heavier elements. Without that we would not be here, because all the elements our planet is made off had been made in another star (and/or in a supernova explosion).

    @Leon

    The inner planets will be in lot of trouble when the sun starts growing. She will become as big as the 1AU which is the present distance between the sun and the earth. So Mercury and Venus will be eaten.
    The earth maybe has a little chance not becoming part of the sun but it will burn up and no place for life anymore. If we do not blow ourself up, or kill ourself by destroying nature (ozon layer, etc) we must find a new place to live.

  25. Edward Cohen

    A very impressive saga. Beautiful pictures.
    This beginner is very awed.
    Keep up the good work.

  26. Brian

    Beautiful, but I think Ken G may have a point also. I think I heard that a red giant blows off mostly its outermost layers, which might be mostly hydrogen (?)

  27. Leon

    DrFlimmer, are you talking about when the Sun becomes a helium burner, or when it becomes a red giant? The situation you’re outlining sounds like what I’ve always understood the red giant status would look like. But will the helium-burning stage entail that kind of growth as well?

  28. Eric

    Thank you Patrick and DrFlimmer

    Very informative about the heavy elements – it’s really amazing to me to think that most everything I know – my house, my computer, the mountains out my window, the ground under my feet – was once spewed out of a supernova.

    I also see upon researching, that as of the big bang, the universe was pretty much 3/4 hydrogen and 1/4 helium, and that only a fraction of a percentage of that hydrogen is used up. I just wonder if someday in the far distant future if the hydrogen “fuel” that forms stars will have been consumed, making it harder for stars to form.

  29. A few followups-

    The outer layers of most stars is still unfused hydrogen. In high mass stars, they blow up and the hydrogen gets scattered. In stars like ours (and Mira) they hydrogen gets blown off in either a strong wind or in those hiccups I wrote about.

    The Sun and nearby stars all tend to be moving at roughly the same speed around the Galaxy, 200 kps or so. Mira is moving relative to that at 130 kps. I think I heard in the press conference today that its orbit has a high tilt compared to other stars, which is a large part of that velocity.

    It’ll be 6+ billion years for the Sun to get to helium burning. So breath a sigh of relief there. It is getting hotter all the time though as helium builds up in the core, but we still have a hundred million years or more before we have to worry about that!

    I read that the disk of material being accreted by the companion (a slightly less massive and cooler star than the Sun) would form planets, but I’m not sure that’s right. I wouldn’t think Mira is blowing off enough material to do that, but I’d have to do some research to find out (and I have too many other things to do!).

  30. Peter B

    Eric said: “It’s really amazing to me to think that most everything I know – my house, my computer, the mountains out my window, the ground under my feet – was once spewed out of a supernova.”

    Not just the things you listed. YOU are made of star stuff.

    How does that make you feel?

  31. Brian

    I just visited the NASA site linked in BAs article above by the words, “The images were taken by the Galaxy Explorer (GalEx) mission.” Then click on “press release” (or some such phrase) to get a nice article by NASA, which complements BAs. It addresses the point raised by Ken G by explicitly saying that the tail contains carbon and oxygen. Nice.

  32. Ken G

    @Leon–
    When the Sun is core helium burning, it will be somewhat like it is now– brighter, but not a giant. What makes it giant is when the core contracts and shells start burning, as the BA described. The Sun actually will do this twice– the first red giant phase, and then the phase Mira is in, which is actually the second red giant phase– also known as the “asymptotic giant” phase, for the usual silly reasons.

  33. gingerbreadcat

    A great article, as usual. By the way, did you ever see Aronofsky’s film “The Fountain”? There are some strong parallels there with Mira. I’d love to read your review of that film anyway.

  34. gingerbreadcat

    Excellent article, as usual. The reality of Mira mirrors some elements in Aronofsky’s “The Fountain”. Though the science isn’t correct, it’s an absolutely beautiful film. I would love to read Bad Astronomy’s take on it.

  35. Tom b

    that was an incredible article and story. thank you!!!!!!!

  36. As the stuff to the left of the image has been ejected 30,000 years ago, what is making it glow “now” in the ultraviolet? (just asking)

    And I suspect there will be traces of it at other wavelengths too so this must be just the beginning of the story

  37. Nigel Depledge

    Another very nice article, Phil.

    Kudos indeed to the astronomer who noticed Mira was fuzzy and went “Hey, that’s odd . . .”.

  38. KaiYeves

    Super cool- and pretty, too! I thought of the Spanish meaning of “Mira”-“Look! Look!”

  39. Kudos indeed to the astronomer who noticed Mira was fuzzy and went “Hey, that’s odd . . .”.

    It’s what we do, darlin’. It’s what we do.

  40. jim

    i no longer believe in big bang. i believe.these processes are eternally & infinitely occurring

  41. Rupert

    awesome!

    one qestion..

    why isnt the star brighter in the picture? is there some sort of filter used in the telescope? judging by the brightness of any old star seen from the most feeble telescopes i would imagine this type of star would be so bright as to blow out all the detail surrounding it.

  42. khazar

    I very much enjoyed reading this article.

  43. Tom

    That’s the coolest thing in a long time! Just amazing, bizarre, and if you think about it a while it just makes your brain go “ping!”. :-)

    One of those things you stare at and realize how small we are.

  44. Kaushal

    Very well written article. Thank you for all your efforts.

  45. Barry Smith

    Mira has been known since the time of the Greeks – they gave it the name Mira. Even then, it was known as unusual – it was a 300 day variable star, visible by eye, in a sky that, at the time, was thought eternal and unchanging. Translating Mira as Wonderful is propably a little off – considering its unexpected variable brightness, it might be better to translate its name as Full of Wonder.

  46. Irishman

    Rupert, go to the link provided by Phil. Scroll to the bottom of the page, there is a comparison picture of ultraviolet light vs. visible light. You can see that the image in question is only ultraviolet. It is much brighter in visible, and the tail isn’t visible.

  47. This is really an incredible image. We get to see the last death-throws of a star as it crawls along, leaving behind a beautiful wake that will itself form new stars one day.

    Great article Phil

  48. Leon

    Thanks, KenG. I wondered.

  49. Mike Thorpe

    The coolest part about this image is that it was on the front page of my local Newspaper, The Vancouver Sun. (Van, Canada). The first time I’ve seen a science story as a headline that isn’t about fear, doom, or gloom.

    Yay science.

  50. yugi

    what a wondeful fairytale. full of mother goose style conjecture. and they call themselves sceptics ?

    nice picture though.

  51. Why (and Who )place(d) the warning that it wasn’t so good for Earth?

  52. beanzie

    mira mira on the wall, who’s the cutest star of all.
    Instead of killing civilians, governments should spend money on telescopes that are bigger than ever. Really really massive ones no less.

  53. David Mills

    Intriguing. Amazingly enough, a substantial number of the comments are less than stupid.

  54. ramzahn

    Mira is really a beauty. Just to imagine how big this star has become…
    But this picture opens a wonderful new vista in my mind. It has scope. Thanks!

  55. StevoR

    Great article – belated thanks BA! :-)

    Very glad I stumbled on this while researching for an article. Mira is, indeed, a superluminously wonderful star which is well-deserving of its name and still capable of astounding us with new surprises. :-)

    Numinious* (exact spelling uncertain – sorry) to think our Sun will one day become a similar Mira variable just before its final nuclear fusing gasps …

    —-

    * See Carl Sagan’s Contact a good SF novel which I’d recommend reading if folks haven’t already.

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