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Researchers Discover a Star's Minimum Possible Mass

Posted by ryuzaki0 on from the must-be-this-large-to-ride dept.

paulmac84 writes "Stars that don't have enough mass never shine, dying billions of years before their bigger counterparts. But astronomers have never been able to measure the exact mass limit, because the lightest stars that do shine can be simply too faint to detect. Now, new images show for the first time how big a star must be to avoid impending doom. The long-awaited new images finally lay this question to rest, say the authors. The dimmest stars were measured as being 8.3% of the Sun's mass. All protostars that are smaller than this are headed for life as a brown dwarf."

27 of 112 comments (clear)

  1. Finally a Definitive Answer! by Aidski · · Score: 3, Insightful

    ...Unless newer technology finds dimmer stars, and they have to lower the minimum again.

    1. Re:Finally a Definitive Answer! by gardyloo · · Score: 3, Informative

      Cute. Though people could just go ahead and read the article. To wit:
      Although the telescope would have been able to detect fainter stars, none could be found- so it appears that they simply don't exist. "We checked the instruments over and over again" said Professor Richer "but we don't see any stars fainter than this".

    2. Re:Finally a Definitive Answer! by Lave · · Score: 3, Interesting
      Sorry to be pedantitc but FTFA:

      Although the telescope would have been able to detect fainter stars, none could be found- so it appears that they simply don't exist. "We checked the instruments over and over again" said Professor Richer "but we don't see any stars fainter than this".

      So they could have detected much dimmer stars but didn't - so assuming a big enough sample, they discovered the minimum mass to initiate fusion. Pretty impressive.

      So finally a Definitive Answer! Until someone bothers to look at a larger sample set,, finds dimmer stars, and they have to lower the minimum again.

      --
      http://skeptobot.blogspot.com/ - A site for the Renaissance man and woman
    3. Re:Finally a Definitive Answer! by cswiger2005 · · Score: 5, Informative

      If there were dimmer stars present there, the Hubble's main camera would have been sensitive enough to have seen them...they're pretty sure of this because they were able to notice some very dim white dwarfs (a white dwarf is the remenant stellar core of a bigger star which went nova; they are very hot [initally] but also very tiny), which are dimmer than the smallest M-class stars still in the main sequence.

      Basicly, this observation is in reasonably close accordance with the theories about stellar fusion; basicly, an potential star needs to have about ten or fifteen times Jupiter's mass before deuterium fusion is possible, and about 70 times Jupiter's mass before normal hydrogen fusion happens (according to the models).

      Jupiter weighs 1.899 * 10^29kg; Sol weighs 1.989 * 10^32 kg (or about 1050 times what Jupiter weighs).
      8.4% of Sol's mass is 1.65 * 10^30, or 87 times what Jupiter weighs.

      --
      "The human race's favorite method for being in control of the facts is to ignore them." -Celia Green
    4. Re:Finally a Definitive Answer! by helioquake · · Score: 2, Insightful

      Photometric uncertainty with the HST/ACS could probably be as high as one percent. There is no way in this kind of astronomy that can determine the percentage good to 0.1%.

      I know what you are getting at: you are basically talking about significant figures, which isn't a bad guess. But here I am referring to more traditional statistical errors that should be propagated through analysis.

      I just read the actual paper and it doesn't have any good estimate on the error.

      Just FYI.

  2. Um... yay? by Capt'n+Hector · · Score: 3, Interesting

    This is a simple math/physics problem. I'm not quite sure what the grand point of it is though (kinda like the pluto(!)=planet debate). Maybe you can graph the distribution of star masses, and then see how much "dark matter" there is on the tail end of brown dwarfs.

    --
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    1. Re:Um... yay? by ZorbaTHut · · Score: 4, Insightful

      Many years ago people believed that heavy things fell faster than light things. They didn't bother testing this theory because they knew it to be true. Then, one day, someone tested that theory and found it was false.

      Perhaps it is a simple problem to answer mathematically. And now we've tested it. We have actual data. Does the data match up with the mathematical answer? Maybe, maybe not, I don't pretend to know. But I imagine people out there do - so either we've got another point of verification that our models are good, or it's time to figure out what's wrong with them.

      Either way, this is what's called Science.

      --
      Breaking Into the Industry - A development log about starting a game studio.
    2. Re:Um... yay? by Artifakt · · Score: 3, Interesting

      It's not quite simple. It's admittedly very simple in the abstract, for a model star where you're only looking at what combinations of temperature and core density allow standard stellar fusion at a break even rate (All normal stars run at break even, in the short enough run, in the sense that the total energy produced is equal to the light pressure keeping interior layers from collapsing, plus the light emmitted to space). Physicists such as Hoyle and Gamow pretty much wrote the math for this at least forty years ago, and much of this was known well before the US designed the "Super" in 1949-50, where it turned out to be applicable (although some of it was so classified then that even the best professional Astrophysicists couldn't assume they had seen nearly all the relevant literature).

              Here's just some of what makes it more complex for the real world though, and I'm probably missing plenty of other complexifying factors:
              Spinning Star? What range of rotation rates occurs in low-mass stars, How much pressure does it relieve at the core at a minimum? (Is there any real occurance of a low mass star with absolutely no rotation?)
              Which Population (I or II). Low mass stars can be very old, as they burn their fuel so slowly. This affects how much of the heavier elements are found in their cores. Just where newer generation stars formed makes a big difference in how much of what heavier elements are in them, but there's not much of a difference theoretically possible for the first generation. Are their faint stars can we observe, but not get enough of a spectrum on to be confident of their composition?
                Are there any convection currents in low mass stars? Do such, as yet unproved, currents include the full range of modalities found in a star the size of our Sun, or fewer? (or maybe even something truly novel, completely different than in bigger stars?). We're not even real sure how typical current patterns within our Sun are for stars of its general type, last I looked.
                Can having a large, close companion star significantly reduce the minimum mass threshold, or would any such received radiation effects be trivial?

      --
      Who is John Cabal?
    3. Re:Um... yay? by munpfazy · · Score: 4, Informative
      Yes it is just a math/physics problem, but it is by no means simple. Sure, if you make a number of simplifying assumptions about convection in a star, you could get an undergrad astrophysics class to tell you the minimum mass of a star. But in reality, the processes that drive convection in a star are incredibly complex, and not entirely understood.


      True enough, but both back-of-the-envelope calculations and the best models give you an answer that's spot on, to within something less than a factor of two. It's not as though there's some great debate within the community about whether the minimum mass for pop-II stars is significantly different from .08 M_sun.

      I'm a great fan of observational confirmations, and of giving Hubble time to people doing this sort of work, but it's hard to imagine why anyone who isn't a specialist in stellar modeling looking to test their code to within a few percent would care about this particular result.

      It hardly seems like press release material. What's more, dressing up the article to make it seem like some great mystery has been solved is disingenuous.

      But, I suppose, "this just in: astronomers have confirmed something that they've been rather confident is true for decades" doesn't sell papers.
    4. Re:Um... yay? by helioquake · · Score: 2, Informative

      I'd add chemical composition (metallicity, namely), too, to your list.

  3. 8.3%? by Anonymous Coward · · Score: 2, Funny

    Apparently, size does matter

  4. For those who are wondering... by Anonymous Coward · · Score: 5, Informative

    ... that's 87 Jupiters.

    1. Re:For those who are wondering... by Anonymous Coward · · Score: 3, Interesting

      I believe that 2010 should still be feasable. It's been a few years, but as I recall it the monoliths descended into Jupiter and used some exotic forces to compact it down to a scale where it was finally dense enough to ignite fusion. This article only speaks to how massive something must be for gravity to compact it that far; theoretically all you really need for a self-sustaining reaction is the proper density and pressure, however those might be achieved.

    2. Re:For those who are wondering... by Null+Nihils · · Score: 3, Funny

      How much is that in Libraries of Congress?

    3. Re:For those who are wondering... by tgd · · Score: 3, Insightful

      Silly, a LoC is a unit of informational quantity, not mass.

      What we really need to know is how many clown-laden Bugs is that?

    4. Re:For those who are wondering... by Dachannien · · Score: 3, Insightful

      Silly, a LoC is a unit of informational quantity, not mass.

      Holy crap, you mean the Library of Congress is massless?!

    5. Re:For those who are wondering... by syntaxglitch · · Score: 2, Informative

      Mostly size, or rather, mass. If you dumped enough hydrogen into Jupiter, it would shine. You just need enough gravitational pressure at the core to sustain hydrogen fusion, which is what the article is discussing.

      That said, relative composition IS different; Jupiter has a dense rocky core of heavier elements (the same sort of stuff the inner planets are made of), surrounded by metallic, liquid, and gaseous hydrogen and some helium. The sun is almost completely made of hydrogen and helium, with a reside of heavier elements, and various layers distinguished mostly by density, temperature, and various physical properties (for instance, the 'photosphere' is the layer at which hydrogen ions render the sun's atmosphere opaque to visible light, and hence is the visible 'surface' of the sun.).

  5. I thought we knew that decades ago. by Biff+Stu · · Score: 4, Funny

    Didn't Karen Carpenter set the standard for the minimum mass of a star?

    1. Re:I thought we knew that decades ago. by kimvette · · Score: 2, Funny

      No, she went below the minimum mass for a star.

      --
      The Christian Right is Neither (Christian nor right). See: Matthew 23, Matthew 25, Ezekiel 16:48-50
  6. So what? by FlyByPC · · Score: 2, Funny

    In Hollywood, the minimum mass of stars has been on the decline for decades now...

    --
    Paleotechnologist and connoisseur of pretty shiny things.
  7. Brown Dwarf? by JanneM · · Score: 4, Funny

    Brown Dwarf? That's "colored star of alternaive height" to you, mister!

    --
    Trust the Computer. The Computer is your friend.
    1. Re:Brown Dwarf? by nacturation · · Score: 2, Funny

      Mister? It's person, you insensitive clod!

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  8. Orson Welles by tverbeek · · Score: 2, Funny

    So apparently Orson Welles - even at his heaviest - was still too "lightweight" to be a real star.

    Ironic.

    --
    http://alternatives.rzero.com/
  9. Re:To the Astrophysicists out there by khallow · · Score: 2, Informative

    Not really. You can't nail down the mass threshhold that well without a huge statistical sample. And even if you could, the luminosity of the star probably would vary a lot around it (ie, it might change a lot if you added or lost a bit of mass). Then there's the matter of rotation. A high rotation rate probably would increase the mass threshhold for fusion. And the luminosity probably changes over time, certainly the mass balance does as the stellar wind blows mass away. Finally, you need some way to calibrate instruments in your lab using this standard. I doubt anyone has a star that they can use as a standard in their lab. Not even the fancy scientists that get to play with the black holes at the center of galaxies!

  10. Re:Hmmmm... by Corwn+of+Amber · · Score: 2, Funny

    The highest possible ego mass for a star must be Francis Ford Coppola then ... or did it collapse under its own weight?

    --
    Making laws based on opinions that stem up from false informations leads to witch hunts.
  11. Brown Dwarfs by some+guy+I+know · · Score: 2, Funny
    what makes a brown dwarf "brown"?
    Two possible reasons:
    1. It's scared shitless of larger stars.
    2. Suntan lotion.
    Also, the politically-correct term for them is "dwarves of color", er, "short stars of color", uh, "stars of color of diminutive ...", ah, ah, "vertically challenged stars of color".
    Yeah, that's it, "vertically challenged stars of color".
    --
    Those who sacrifice security to condemn liberty deserve to repeat history or something. - Benjamin Santayana
  12. For a little perspective... by damburger · · Score: 2, Interesting

    8% of the Suns mass is still about 100 times the mass of Jupiter. So all that crap about turning Jupiter into a star in "2010" was a load of bollocks. Like, well, pretty much everything in that shite film.

    --
    If we can put a man on the moon, why can't we shoot people for Apollo-related non-sequiturs?