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Space Science

Binary Star EF Eridanus Baffles Astronomers 57

Posted by michael from the sucked-dry dept.
baldinux writes "Reuters is reporting the finding of a new stellar object in the Eridanus constellation that may require the astronomical community to create a new category of stellar entities -- that is, dead ones. In the binary system, one of the stars 'gave too much' (Reuters) of its own resources to its partner white dwarf star, resulting in a breakdown of nuclear fusion, thus producing this 'dead' entity. Researchers at Gemini North (click here for images) and Keck II observatories at Mauna Kea, Hawaii, have been analyzing this unique system."
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Binary Star EF Eridanus Baffles Astronomers More

Binary Star EF Eridanus Baffles Astronomers

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  • In human terms... (Score:5, Funny)

    by Anonymous Coward on Wednesday October 06, 2004 @01:39AM (#10448256)
    In human terms this is known as marriage.

  • They should name binary pair... (Score:5, Funny)

    by bobdotorg ( 598873 ) on Wednesday October 06, 2004 @02:07AM (#10448329)
    They meet, they accrete, and then dance for years as they happily twirl about. But as time goes by her ass grows more massive as she sucks out his soul and he becomes a shadow of his former self.

    So I propose the name: Succubus and the Bitter Old Man.
  • And the dwarf finds itself in quite the pickle without a new host to feed on (look out earth).

  • Probly Classified as an L or a T dwarf (Score:4, Informative)

    by aws4y ( 648874 ) on Wednesday October 06, 2004 @05:12AM (#10448839) Homepage Journal
    Though it may have lost its hydrogen and helium burning capeability I would hypothesise that the thing is now an L or T dwarf that is to say it might be Duterium or Lithium burning, or its spectral profile might be very dusty or contain methane. In otherwords we might have just seen an L or T dwarf being made but I highly doubt this is a new class of star.

    • Re:Probly Classified as an L or a T dwarf (Score:1, Informative)

      by Anonymous Coward
      From the article;
      the burned-out star has lost so much mass that it can no longer sustain nuclear fusion at its core
      I think they are talking about a "star" that doesn't really shine (any more than Jupiter does). I don't understand what the big deal is. We know what it is. It is a star that has lost mass. So when we find more like it, we can say "Whoa. This must have been a star. And it has lost mass somewhere. Time to more on to the next thing."

    • Re:Probly Classified as an L or a T dwarf (Score:5, Informative)

      by DLWormwood ( 154934 ) <[moc.em] [ta] [doowmrow]> on Wednesday October 06, 2004 @11:08AM (#10451384) Homepage
      In otherwords we might have just seen an L or T dwarf being made but I highly doubt this is a new class of star.

      From the article...

      "Now the donor star has reached a dead end -- it is far too massive to be considered a super-planet, its composition does not match known brown dwarfs, and it is far too low in mass to be a star... There's no true category for an object in such limbo"

      The unstar appears to fall between the cracks of current astronomical classification...

      • Someone put an order in to Edmund Scientific! We need a new category and we're all out! What WILL we do?
      • "From the article...

        "Now the donor star has reached a dead end -- it is far too massive to be considered a super-planet, its composition does not match known brown dwarfs, and it is far too low in mass to be a star... There's no true category for an object in such limbo"

        The unstar appears to fall between the cracks of current astronomical classification..."

        Hmmm... how about having part of the name being the type of star that it used to be before it's binary partner gobbled up too much of it's matter, and

    • Re:Probly Classified as an L or a T dwarf (Score:4, Informative)

      by Christopher Thomas ( 11717 ) on Wednesday October 06, 2004 @01:54PM (#10453034)
      Though it may have lost its hydrogen and helium burning capeability I would hypothesise that the thing is now an L or T dwarf that is to say it might be Duterium or Lithium burning,

      This seems unlikely, as both D and Li burn a lot more readily than p, if I understand correctly. Thus, the star should have used these up very early in its life. If it started life as something larger than a red dwarf, you could argue that there would be deuterium and lithium in its outer layers that wouldn't have mixed with the core material, but a) the outer layers were mostly what was stripped off by the companion star, and b) the star would have passed through a red dwarf stage as it lost mass, resulting in more thorough mixing during that time period.

      So, I'm not sure it's a good bet to say that there would still be D or Li left. What do the spectrographs say, for this object?

      or its spectral profile might be very dusty or contain methane. In otherwords we might have just seen an L or T dwarf being made but I highly doubt this is a new class of star.

      I'm not sure "star" is the correct term any more, as there's no fusion happening (in all likelihood). A few classifications I can think of:
      • Stellar remnant.
        Pretty broad category, so probably not specific enough. Also tends to refer to things like planetary nebula and not stars (we haven't seen anything star-like that's been around long enough to cool down past "white dwarf" levels).

      • Black dwarf.
        It's a stellar core that can no longer sustain fusion. But this term usually refers to the (as yet unobserved) cooled ashes of a burned-out stellar core (cold white dwarf).

      • Brown dwarf.
        It's a sub-stellar mass that's still massive enough that it probably could sustain deuterium fusion, if it had any deuterium to fuse. That probably makes it a brown dwarf on a technicality, even though it's of a bizzare spectral type compared to other brown dwarfs (as you point out).

      • MACHO.
        This is another category that's probably too broad to be useful. If it's stripped to below the point where deuterium fusion can occur, but is not a planet (i.e. condensed from a nebula directly as opposed to from another star's protoplanetary disk), it probably counts as a MAssive Compact Halo Object, on a technicality.


      I'm voting for "brown dwarf" or "black dwarf", but those are still on technicalities.
      • Thus, the star should have used these up very early in its life.

        Deuterium and tritium are byproducts of the pp chain - the star constantly regenerates them.

        Once the pp chain stops, deuterium burning will continue for a while (stars are *big*, after all) but would, eventually, stop.

        Spectrography might be able to detect the relative ratios of deuterium, etc. in the object, but not likely - its core is still quite dense, and there's little light being generated from there.

        Pretty broad category, so prob
        • Deuterium and tritium are byproducts of the pp chain - the star constantly regenerates them.

          Fair enough. However, these should have been burned very quickly, as when pp fusion stopped, the star would have been *well* within the envelope for rapid DD fusion, and probably a lot of lithium fusion paths as well. This would have occurred while the star was still in pp fusion mode, too; the p + p reaction is the rate limiting step (requires a Weak transformation, which is extremely unlikely compared to Strong i
          • So little, if any, D and Li should have been available at the time pp fusion ceased.

            You're right that the D and Li phases wouldn't last much longer afterward pp stopped, though it depends on the mass loss rate. But there would've been a fair amount of D and Li available.

            Actually, the D burning would continue probably for quite some time due to hydrodynamics, now that I think about it. While fusion was occurring, the turbulence inside the star would dominate the hydrodynamics, so D would remain mixed thro
            • You're right that the D and Li phases wouldn't last much longer afterward pp stopped, though it depends on the mass loss rate. But there would've been a fair amount of D and Li available.

              I'm not convinced of this, for reasons mentioned in my previous post - as pp -> D e+ ve is the rate limiting step, the amount of D present at any given time would be miniscule (it's burned far more quickly than it's produced, so remaining D represents the tail end of the survival time distribution). Any that is left wh
              • I doubt there'd be much D outside the active part of the core, as a) it's only produced in the active part of the core, and b) as the active region shrank as the star lost mass, it would be surrounded by a region in which D could still burn - so the D left in the areas that were once core would be burned up almost immediately.

                I was actually thinking about the unburned D in the outer stellar envelope. I'm not sure how much there would be, though - I can't find measurements of the Sun's deuterium abundance
                • I was actually thinking about the unburned D in the outer stellar envelope. I'm not sure how much there would be, though - I can't find measurements of the Sun's deuterium abundance in the outer region of the star. The reason I was saying so is that with hydrogen burning, the star actually stops burning hydrogen far before it runs out of hydrogen in the star - it's just that the outer shell hydrogen has no chance to reach the core so long as the star burns at all.

                  This is only true for stars about the size

  • See: altruism is evil. (Score:3, Funny)

    by Chemisor ( 97276 ) on Wednesday October 06, 2004 @08:18AM (#10449585)
    > In the binary system, one of the stars 'gave too
    > much' (Reuters) of its own resources to its
    > partner white dwarf star, resulting in a breakdown
    > of nuclear fusion, thus producing this 'dead' entity.

    A good example to illustrate the evil of altruism.
  • ... the locals found that they had enough light with one star already and did not need to run their backup fusion powerplant. *switch*

  • Dead star (Score:3, Interesting)

    by mknewman ( 557587 ) * on Wednesday October 06, 2004 @08:46AM (#10449781)
    I think this sort of star has been postulated for quite a while, especially with black holes and neutron stars sucking material out of companion stars, but this is the first observation of the result of that process, a star that is no longer fusing. It's a dead husk. I think that makes it a supergiant planet or an ex-star, but I doubt it's fusing anything anymore. It's been sucked dry.
  • IANAC (I am not a cosmologist)
    AINAA (I am not an astrophysicist)
    IAAAJ (I am an average joe)

    Could the dwarf star absorb enough mass that fusion could start again? That would be awesome!

    • Re:Could this "re-ignite" the dwarf star? (Score:5, Informative)

      by barawn ( 25691 ) on Wednesday October 06, 2004 @01:27PM (#10452831) Homepage

      Could the dwarf star absorb enough mass that fusion could start again? That would be awesome!

      This is what novae are (not supernovae, which are different). When a white dwarf star accretes matter, it builds up on its outer shell. Since the white dwarf is incredibly dense, its gravity is incredibly strong, so the layer of matter (hydrogen) is incredibly hot. Eventually the density of hydrogen grows enough that fusion can occur again, and it does - and the star burns off (very quickly - ~few days) what took it several years to build up.

      This causes a white dwarf to go from barely visible to extremely bright. In the night sky, it looks like a new star comes out of nowhere, then disappears - hence the word "nova", meaning 'new'.
  • It is an oddball arrangement they have never seen before, but the only baffling thing is what to call it. It's way too big to be a supergiant planet, but it has been drained down and "switched off" the shining process so it doesn't qualify as a star anymore.

    An interesting addition to the stellar zoo, but probably of little scientific signifigance.

    -
  • "Like the classic line about the aggrieved partner in a romantic relationship, the smaller donor star gave, and gave, and gave some more until it had nothing left to give," said astronomer Steve Howell

    Gave? Methinks it was TOOK! (All the telltale signs are there -- oh, sorry, I'm trying wean myself from CSI.)

  • Naming a new category is not possible anymore...I foresaw this and patented the process of developing AND implementing new categories. This new career RULES!!! since I've been too STUPID in the past to develop a REAL business plan! Mod this: -16 for OFFTOPIC -10 for FUNNY -pi for INFORMATIVE
  • OK, the donor "star" no longer has enough mass to maintain fusion, but it's still a big compressed ball of (mostly) hydrogen and helium, held together by gravity. The white dwarf "vampire" star is still sitting right there.

    So what caused the process to stop? Why isn't the vampire still sucking on the donor?

    Maybe it is, and we can't see it, (even though I suspect we'd see something as the matter was gravitationally accelerated into the vamp star.

    Or maybe the two are farther apart than they used to be, e

    • It's not fusing internally any more, so it's cooling down and shrinking. Its "surface" is deeper in its gravity well and colder, so it's not getting stripped away as quickly. The vampirism probably hasn't stopped, just become too small to detect.

      Also, the thing probably has much higher concentrations of "metals" than typical brown dwarfs or gas giants...for a while, it was fusing, and it probably lost lighter elements to the white dwarf more easily.
      • I'm not sure about that.

        Since it's a binary system, we'll assume that the two are cosmologically the same age, meaning that whatever generation they are, we're looking at roughly the same elemental mixture at birth (ignition), which we should be able to get from the dwarf's (vampire's) stellar spectra.

        I'll further posit that as the vamp star went through the nova phase, between 30 and 50 percent of the expelled mass would have been absorbed by the donor star (they're that close), but this would have been

        • Since it's a binary system, we'll assume that the two are cosmologically the same age, meaning that whatever generation they are, we're looking at roughly the same elemental mixture at birth (ignition), which we should be able to get from the dwarf's (vampire's) stellar spectra.

          They're not the same mass, though. And since the white dwarf companion is - well - a white dwarf, it obviously was far more massive. It burned out first, for one.

          A white dwarf's elemental composition, moreover, is not a good indic
        • When it goes nova, the white dwarf casts off most of the matter it gains, so it stays at nearly the same mass. However, the donor star is no longer fusing, so it cools and shrinks. As it becomes cooler and more compact, its "surface gravity" increases and the average molecular velocity goes down, both effects slowing the mass loss. It'll lose lighter elements preferentially, especially as it cools and heavier elements combine into even heavier molecules, while helium stays as single atoms and hydrogen mostl
    • OMG! OMG! OMFG! I left an open paren on this! I'm __SO__ embarressed! Bad spelling is forgivable, but a syntax error! gulp.
  • How is this suprising? There are no rules saying how big a body of gas in space can be, so scientists are to blame for the fact that their classification system does not have enough room in it for bodies of a certain size. I can't see how this is a revalation, more of just finally finding something of the right size.
    • I can't see how this is a revalation, more of just finally finding something of the right size.

      It's the same size as a brown dwarf. The problem was that no one had found anything that's the same size as a brown dwarf, but not a brown dwarf (i.e., an object condensed from a nebula/disk but not large enough to complete the pp-chain at its core).

      Things are classified typically by mass and composition. Almost everything falls into certain classes by those rules (stars, brown dwarves, white dwarves, planets,

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