The Ghost in the Shell

By Phil Plait | July 5, 2012 7:00 am

Stars are one of the fundamental building blocks of the Universe. Huge, hot, and powerful, they emit energy that can be detected across vast reaches of space. For as long as they live (so to speak) they glow with a fierce luminosity.

And even when they die they can announce their presence in weird and wonderful ways.

Meet U Camelopardalis, just such a dying star about 1400 light years from Earth:

[Click to doomsdaymachinenate.]

U Cam is a red giant, a star that was once like the Sun but has gone much further along its evolutionary path. Our Sun is fusing hydrogen steadily into helium in its core, providing warmth and light for us. U Cam ran out of hydrogen in its core long ago, and began fusing helium into carbon. Then it even ran out of helium as a fuel! The core is now essentially an extremely hot ball of carbon, squeezed by pressure to within an inch of its life. There’s still helium outside the core, and gets so much heat from the core’s radiation that it’s fusing in a thin shell. Think of it like a very hot skin around an orange.

This helium fusion is ridiculously dependent on temperature. Increase the heat just a wee bit and the fusion rate increases madly, generating huge amounts of energy, which get dumped into the outer layers of the star on very short timescales. And by "short" I mean like years. Not millions of years. Just years.

When this happens the star swells immensely and ejects its topmost layer, like a solar wind on cosmic steroids. This event doesn’t last long, maybe a century or so, then it subsides. But that shell of ejected gas expands out from the star, eventually dissipating over millennia.

And that’s where U Cam is right now. Not long ago its core underwent one of these paroxysms, and the star blasted out the shell of material you can see in this Hubble Space Telescope image. Measuring the expansion rate, it looks like this shell was ejected about 700 years ago, and the event only took 50 years to unfold! Because these events don’t last long compared to the life of the star, it’s rare to see them. U Cam is one of the best of only a handful of such stars known.

In the image you can see how thin the shell is, indicating the event happened rather quickly (if it took a long time the shell would be thicker). I’ll note that the total mass of the shell is only about a tenth the mass of the Earth! It’s spread out over so much volume of space that it’s barely more dense than the vacuum surrounding it.

The star itself is actually just a dot on this scale, but is so bright it overwhelmed the detector a bit and looks far bigger than it really is. Those light and dark radial spikes are not real; they’re artifacts of the way the camera sees light from a star. They’re enhanced in this picture somewhat more than normal because the astronomers used another image of a star to subtract from this image to reduce U Cam’s brightness – that lets the fainter shell be seen more easily. When I worked on Hubble I wrote a lot of software to do this kind of thing, and I saw spikes just like that in all my data. Irritating for science, but kinda pretty in the picture.

But this is more than just a pretty picture. What we’re seeing here is a glimpse of our own future. Our own Sun is on the same path as U Cam. In a little over 6 billion years the Sun will run out of hydrogen in its core, and about 1.5 billion years later will run out of helium to fuse as well. At this point, 7.75 or so billion years from right now, the Sun will be very much in the same position as U Cam. It will undergo as many as three or four of these shell-emitting events, each blasting out a thin bubble of gas and dust that will expand away, eventually to merge with the ethereal material floating in between the stars. By the time the last one erupts, it will strip away the last outer layers of the Sun, exposing the hot white dwarf of its core, which, over tens of billions of years, will eventually fade to black.

But take heart! By then the Earth will have been long dead anyway, scorched to a cinder when the Sun was a red giant!


Actually, considering we’re talking about timespans of hundreds of millions and billions of years, I’m rather hopeful that by then humanity will have found other, more youthful stars to live near. Or who knows, maybe by then we won’t even need to live on warm planets. Predicting how stars will change over eons is relatively easy; understanding where people will be even in mere decades is a fool’s game. But I can hope, by the time our own star dies, we’ll have found some way to move on. The Universe is large and deep, both in space and in time. There’s plenty of room to grow.

[NOTE: I have an entire chapter with details and a timeline of how our Sun will grow old and die in my book Death from the Skies! Just so’s you know.]

Image credit: ESA/Hubble, NASA and H. Olofsson (Onsala Space Observatory)

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CATEGORIZED UNDER: Astronomy, Pretty pictures, Top Post

Comments (27)

  1. LH Ld Elon

    From the crash was truth,
    from ther after was not!
    A legend then was sought,
    where truth lay to rot,
    upon the land in swaythes,
    its lies pathed way for many slaves,
    until the day the righteous born,
    mans future looks as bleak and scorn,
    and when they rise with glory bound,
    the harmony essence of peaceful sound,
    pondering on all theyve seen and found,
    they wait in peace to except their ground…

  2. Nigel Depledge

    But take heart! By then the Earth will have been long dead anyway, scorched to a cinder when the Sun was a red giant!

    Always look on the bright side of life.

    That’s what we love about you, Phil.

  3. Kyle

    When I first saw the image I figured it was an artist conception, that that is a real image blows my poor little mind! In the words of Phil “Holy Haleakala” that’s incredible.

  4. Chris A.

    When I first saw this, the spikes made me think “that can’t be a photo–it must be an artist’s rendering.” The fine line between art and science.

  5. D. Stark

    I’d be most curious to know the radius of that shell. How “big” are we talking?

  6. Ben

    The image looks a lot like an eye, uncannily so if you invert it.

  7. Er, BA, looks like those first two links are identical, not sure if that was intentional?

    Great image and write up, cheers! :-)

    What’s U Camelopardalis’es visual range & period btw? Going from the name it sounds like it should be a reasonably bright variable (Mira -type I presume?) star albeit probably too far north in the sky for me. Anyone here been observing it?

    Not long ago its core underwent one of these paroxysms, and the star blasted out the shell of material you can see in this Hubble Space Telescope image.

    Those “paroxysms” would be the helium flashes is that right?

    PS. Linked Kaler’s photographic finderchart of Camelopardalis to my name here if that helps or is of interest to folks, just to the side of Capella and Auriga. U Cam not marked there tho’.

  8. Lee from NC

    I was thinking along the lines of Ben (#6)-sometimes the abyss stares back. Cool!

  9. Dutch Railroader

    We’re looking right into the maw of the Doomsday Machine. “They say there’s no devil, Jim, but there is…”

  10. A.K. Bean

    I love that I can hop on the internet and see the future (or the past in some cases.) Space is beautiful.

    Ghost in the shell is a great (2) movies, also!

    This blog entry of yours makes me think of a particular line from the first GiTS movie.

    I’m not really one for bible quotes usually, but I find it interesting that we take a phrase from one century and it gets reused over and over in different echos in literature.

    For now we see through a glass, darkly; but then face to face: now I know in part; but then shall I know even as also I am known.
    -Corinthians 13:12

    But now we see through a glass darkly and, the truth, before it is revealed to all, face to face, we see fragments (alas, how illegible) in the error of the world, so we must spell out it’s faithful signals even when they seem obscure to us and as if amalgamated with a will wholly bent on evil.
    -The name of the Rose by Umberto Eco

    ”For now we see through a glass, darkly.”
    -Ghost in the Shell

    It’s strange how it’s always the vague poetic phrases that stick with us. (I wonder if there will be a time when the original quote will be forgotten, maybe there was even a source before the bible we have no inking of

    Isn’t that how we look through telescopes? We have to piece together views of tiny images and squeeze out an understanding of them with software and layering, sometimes with pictures taken from different light wavelengths. Sometimes we have to discard our entire understanding of a cosmic (literal) event, other times we find our predictions vindicated.

    Every time is wonderful. I love the adventure of it all, even if I’m sitting at my desk going through my RSS stream, even if we’re not out there galloping on space horses into the setting supernova.

    Information is fantastic.

  11. StubbyGB

    I’m with #5 D.Stark, anyone know how big that shell is ?

  12. HvP

    I think that whatever intelligent life which may inhabit the Earth six-billion years from now would be nothing like what we call humans, and may not even be descended from humans. It was only one-billion years ago that single-celled organisms evolved into multicellular organisms.

    The time between now and when the Sun goes kaboom is nearly double the time covering the entire history of life up to this point. It’s more likely that the evolutionary clock will have been reset multiple times for many different reasons before our Sun swallows us up.

  13. Ty

    OK Phil, you’ve convinced me to buy your book!

  14. Gary Ansorge

    I expect, long before that time, our silicon descendants will have moved on to another galaxy…

    Gary 7

  15. Chris

    “Where does the newborn species go from here? The web of stars is vast and infinite…”

    GitS: awesome movie. I prefer the two-season series, though. It took the best parts of the manga and movies and blended them together.

  16. Jess Tauber

    Assuming our species continues (into others, or not), a couple of billion years of technological development ought to considered, non?

    Aside from us moving, we could move the earth. Renew its core while we’re at it so plate tectonics doesn’t shut down. Do the same for the sun- be good chimney sweeps, as it were. We’ve got the time. Bring in fresh H from beyond, dump no goodnick He. All sorts of possibilities.

  17. And look, its spherical! That may be pretty rare in terms of what will eventually lead to a PN. No companion star then no bright visible shell (U Cam is pretty close though)

  18. Wayne Johnson

    And this already happened a couple of times “here,” right? Our sun is a 3rd or maybe 4th generation star. I suppose that ejected material coalesced into dust rings and thence into planets.

    Maybe the same thing happened at generation 2, and life evolved there. When that sun went nova, a few rocks survived to carry life from the new Heaven onto the new Earth.

    That would explain why life appeared on Earth very quickly, as soon as the first rocks cooled enough to solidify.

  19. Joseph G

    @16 Jess Tauber: As long as we’re throwing out sci-fi scenarios, I wonder if planetary nebulae like this would make useful refueling stops for interstellar ships? Like a motherlode of hydrogen for ramscoop-type ships becalmed in relatively empty regions of the interstellar medium?
    If I understand correctly, only relatively small stars (smaller than our own sun) are fully convective. That means that material blown off of a star with a core depleted of hydrogen will still be mostly hydrogen(?)

  20. RobT

    Actually, when I first saw the picture I thought it was of a Cloud Chamber, aka Wilson Chamber. The colour is what made me think it was something else.

  21. Doug Bostrom

    Very curious to know what are the spokes or rays extending from the star?

  22. beerclark

    @ Doug Bostrom: B.A. mentions those spokes. That is from the camera itself. Or an effect from the camera viewing a star. They are not really there.
    From B.A. in the article.
    ” Those light and dark radial spikes are not real; they’re artifacts of the way the camera sees light from a star …………. When I worked on Hubble I wrote a lot of software to do this kind of thing, and I saw spikes just like that in all my data. Irritating for science, but kinda pretty in the picture.”

    My question is, how fast and how far is the gas?

  23. Dan

    From what I’ve read, Earth is going to be uninhabitable for humans and other mammals within 500 million years or so thanks to the constant rise in the sun’s temperature that’s occurring even now. Within a billion years all water will have boiled away. So we don’t have 6 billion years to play with. The age of animals is already well past its halfway point.

  24. Vulcan Tourist

    Jupiter and Saturn at the least have some hydrogen, eh? We should set up an intravenous feeding tube to feed dear old Sol some more of what it needs.


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