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Space Science

Planet-Gobbling Star 85

Posted by timothy from the this-is-my-theory dept.
crymeph0 writes "BBC is carrying a story about a star that mysteriously brightened three times last year. Scientists now know why. It's been eating gas-giant planets that orbit it! I'm just glad Earth isn't a tasty gas planet, or else we'd have to start making sacrifices to Sol to play it safe." It's hard to prove things from 20,000 light years away, but this explanation is interesting.
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Planet-Gobbling Star More

Planet-Gobbling Star

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  • Right then... (Score:5, Funny)

    by Anonymous Coward on Wednesday September 17, 2003 @03:25PM (#6988183)
    so it's just a case if indigestion, then?

  • I read a paper on something related to this (Score:5, Interesting)

    by Zachary Kessin ( 1372 ) <zkessin@gmail.com> on Wednesday September 17, 2003 @03:32PM (#6988266) Homepage Journal
    In stars where there is a much higher level of "metals" seem to generate more large planets than we have. It seems that in a star like this you may end up with 4-10 Jovian size planets. In the case of our solar system you have 2 very large planets and everything is far enough appart that it is stable. On the other hand if you had a bunch of planets at 10 Jovian masses it is inevitable that a few would be kicked out of the system and a few put into very close in orbits.

    it all comes down to how much matter there is to create planets. The higher the densisty of heavy elements the faster things start to clump into planets, and the bigger the planets get.

  • uh-oh (Score:4, Funny)

    by Tumbleweed ( 3706 ) on Wednesday September 17, 2003 @03:35PM (#6988305)
    Somebody call Commodore Decker and Captain Kirk!

  • Zen of the Day (Score:2, Funny)

    by Anonymous Coward
    ZOTD:

    Is the star brighter, or is everything else just darker?

  • Orson Wells? [doubleclick.net]

  • a new standard candle? (Score:3, Interesting)

    by Ckwop ( 707653 ) on Wednesday September 17, 2003 @03:41PM (#6988364) Homepage

    Perhaps we have a new standard candle in the making here. Perhaps this effect is closely tied to the starting mass and composition of the solar system of the star.. and thus the brightness is roughly the same for each event..

    Just a thought :)

    Simon

  • *cue cool music*

    Unicron: For a time, I considered sparing your wretched little planet, Cybertron! But now, you shall witness... its DISMEMBERMENT!

  • In related news.. (Score:5, Funny)

    by ewhenn ( 647989 ) on Wednesday September 17, 2003 @03:43PM (#6988382)
    Prevacid stock has spiked sharply up.
  • I'm just glad Earth isn't a tasty gas planet, or else we'd have to start making sacrifices to Sol to play it safe

    If our sun some day decides to turn into a Planet-Gobbling Star, let me know. I will go to the church and pray to the Almighty to send the devilish sun to Hell !!

  • Someone get Skywalker and Solo, ASAP!

  • Prilosec (Score:1, Funny)

    by Anonymous Coward

    Prilosec went over-the-counter Monday...

  • Carnie Wilson (Score:3, Funny)

    by AtariAmarok ( 451306 ) on Wednesday September 17, 2003 @03:46PM (#6988410)
    I saw the headline and figured "Oh no! Carnie Wilson is off her diet again!"

  • Sci Fi nuttery from me (Score:4, Interesting)

    by Henry V .009 ( 518000 ) on Wednesday September 17, 2003 @03:56PM (#6988490) Journal
    I imagined for a second an advanced civilization crashing gas giants into their sun to keep it alive a little longer. I am wrong, of course, and this is no doubt the work of gravity, but I would like to point out that if we ever decide that we would like to keep our Sun burning for an extra million years or so, the only way to do that will be to crash Jupiter into her. On the other hand, the energy expended to do that would probably be better expended in creating environs that can support life without a sun.

    • You know, that probably could form the foundation of a neat short story or novel. You'd have to do a lot of tinkering with the physics and math to make it believable, but even so...

      HBH

    • This has been written before (Score:4, Informative)

      by devphil ( 51341 ) on Wednesday September 17, 2003 @04:50PM (#6988951) Homepage


      Read Niven's A World Out Of Time (multiple meanings in the title) for a similar idea. It's one if his first "State" books.

      SPOLIERS BELOW

      Basically, something else gets dropped into Jupiter. And there's some fascinating ideas on how to move a planet around.

      • Read Niven's A World Out Of Time (multiple meanings in the title) for a similar idea. It's one if his first "State" books.
        Oddly, I just picked that up again last night. It's based on his short story "Rammer". Here's a review [larryniven.org].
    • It sounds kinda cool to go ahead and fuel our sun with a giant gas planet, but then the resulting burst of energy would probably decimate all life on our planet. "Oops! Sorry! My bad..."

      Then again, it just has ya thinking about "hm, well we could shoot all our nukes or other sources of fuel to the sun to feed it in controllable ammounts." This also rids our planet of them. But like you said...all that time, effort, and energy could be spent on other forms of life preservation and exploration. Sure is fun
    • Wouldn't a civilization capable of crashing Jupiter into the sun also be capable of colonizing nearby galaxies? By that time, earth would have been long-forgotten, the remaining residents having left after Dubya XXIV declared the sun a rogue celestial body since Osama bin Laden (still in hiding) orchestrated a terrorist attack on OneWorld headquarters in Texas during the daylight hours.
    • Comment removed based on user account deletion

  • Time for a Mars bar, yum! (Score:5, Funny)

    by G4from128k ( 686170 ) on Wednesday September 17, 2003 @03:58PM (#6988521)
    OK, its more a Jupiter bar -- a chewy metallic hydrogen center covered in rich fluffy methane-ammonia clouds. What every growing star needs for a burst of energy.

    How many orbits does it take to get to the center of a gas-giant lollipop?

  • A Couple Thoughts/questions (Score:4, Interesting)

    by CheshireCatCO ( 185193 ) on Wednesday September 17, 2003 @03:59PM (#6988529) Homepage
    1. They're positing that eating one or three giant planets is enough new fuel to make the star brighten significantly? (I wish the article had the details on how much it actually brightened.) A typical gas giant is around 1/1000 the mass of the parent star. That's not a lot of new fuel, particularly when you consider that the star has way more hydrogen than that left over from main sequence burning.

    2. My most recent understanding (and I admit that I'm only half paying attention to this) is that the planets-contaminate-stars model for the heavy element enrichment probably doesn't explain the observed enrichment. (Probably because the planet's bits would have to stay right near the star's surface over the long run. See mass ratio, above.)

    I'm not saying that this model doesn't work, but I'm skeptical. I'd really want to see their stellar models showing how addition of a giant planet's mass of hydrogen on the surface of the red giant affects the luminosity. I'd also like to see evidence that this star had planets before the brightening. (I wouldn't be shocked if the data didn't exist. But I still want to see it. :-)
    • 1) (I wish the article had the details on how much it actually brightened.)

      From the article: The star was seen to brighten to more than 600,000 times our Sun's luminosity.

      Well, it's not a hard number, but it's something.

      2) the planets-contaminate-stars model for the heavy element enrichment probably doesn't explain the observed enrichment.

      Well, since we have a fairly good idea that the fusion process ends rather abruptly when the number of protons in the newly-created element reaches Iron (Fe), even

      • Re:A Couple Thoughts/questions (Score:4, Informative)

        by CheshireCatCO ( 185193 ) on Wednesday September 17, 2003 @06:01PM (#6989532) Homepage
        1) See, I asked about how much it *brightened*. Not how bright it *got*. I noted that line, too., but knowing that it is now 600,000 L_sun isn't really helpful in telling us how much brighter it is now than before. We would need to also know what its starting point was. This makes a difference: if the star brightened by 0.1%, the possible mechanisms are quite different from the star brightening by a factor of 100.

        2) Um, no. When a star gets to Fe (and only very large stars do), it makes a nice little explosion adn we enrich the interstellar medium. Which is where pretty much all of the "metals" (anything heavier than helium, according to astrophysicsists) in your body, Earth, the Sun, etc. come from. So the question about metal-rich stars isn't "are they producing the metals", they would have had to leave the main sequence for one thing. The question is did the cloud that formed them have an more metals than the average, or did the metals get preferentially introduced by, say, planets smacking in to them.

        No, see, as star is WAY bigger than a planet. (By definition, almost.) So a planet, particular a gas giant which is in large part hydrogen and helium (10s of percent and up, by mass) smack into the star, unless the material stays right near the surface, all of those metals will basically be so thinly spread throughout the volume of the star that you'll never see a real enrichment to within error bars.

        And remember, the volume of a shell goes like the radius or the star squared, so the thickness of the shell has to be pretty thin to keep an appreciable fraction of the metals. Say we want to spread the metals out over a volume roughly equal to the volume of the original core. Uranus is mostly core, so let us use its radius as the radius of the core. (Note: much of Uranus's core is hygrogren compounds, as are all giant planet cores. This means that we're *over*estimating the volume of metals.) And lets spread it over a spherical shell on the Sun's surface.
        V_Uranus = 4/3 pi r_u^3
        V_shell = 4 pi r_s^2 deltaR
        where r_u is Uranus's radius (2.62E9 cm) and r_s is the Sun's (6.9E10 cm), deltaR is the thickness of the spherical shell, and the Vs are volumes. Equating and cancelling, we get that deltaR = r_u^3/3 r_s^2. Plugging in numbers, that's a thickness of about 1.3E6 cm, or about 0.0018 % of the Sun's diameter. Which, when you consider that the Sun is fluid and convection does happen (although the most convective part is a bit lower down below the surface), isn't a whole lot. Confining the metals to that region would be very difficult.

        This would probably be why current thinking tends more towards the "the clouds that formed star with planets were unusally rich in metals." Also, it makes sense: more metals, more stuff to actually *build* planets with.
        • I don't think that they're positing a persistent luminosity increase due to fusion; I think that they're claiming that the thermal enery of the impact created a transient spike in the stellar brightness. That's not as wild as it seems: you're talking about a gas giant with 0.001 Solar Mass. That's gonna create a lot of kinetic energy to dissipate.

          As to the metal enrichment thesis, though, yeah, that does seem pretty bogus.
          • "The researchers say that V838 Monocerotis flared because it was fuelled as it engulfed three orbiting planets. It could be the first evidence for an event that had been predicted but not knowingly observed.

            Support for this assessment, say the astronomers, is provided by the study of the shape of the light curve and comparison between the observed properties of the star and several theoretical studies.

            In addition to the gravitational energy generated by the process, there may also have been a rapid releas
            • Without looking at the numbers, I'd suspect that most of the energy that they do add gets added rather far down into the star, so that it won't leak out as one, bright flash.

              The mechanical (potential + kinetic) energy E of a small mass m and velocity v a distance r from mass M is given by

              E=mv^2/2-GMm/r

              If we assume m is orbiting in an approximately circular orbit (the argument works even if the radius is slowly decaying), then v = (GM/r)^.5. Thus

              E = mGM/(2r)- GMm/r

              = -GMm/(2r)

              Differentiating w/ respect t

              • You made a mistake, though. (The same one I made at first with this calculation.) The planet is being engulfed by the star, which is expanding out to it. Which means that the planet isn't moving inwards to the star, the star is moving out to *it*. So the star doesn't gain the PE from the planet's orbit, at least not much. If the planet does move inward into the star, most of that energy comes at the expense of moving more fo the star upwards against the star's gravity. (You'd basically have convection
                • You made a mistake, though. (The same one I made at first with this calculation.)

                  Nobody made any mistakes, because nobody knows what really happened. Elsewhere [nasa.gov] there are examples of gas giants orbiting within 3-7 million miles of their stars' surfaces. Perhaps the enormous mass loss rate is bleeding the gas giant of its orbital angular momentum and essentially driving it into the star that is frying it. Or if the star is rotating slower than the planet is revolving around it (the previously mentioned

                  • Red giants are quite large. Even the Sun in that phase will probably be large enough to reach Earth's orbit. An F-class star is larger, so we can assume that these weren't hot Jupiters that got envelopped.

                    And, yes, distance DOES matter. If the planet never falls into the star (the star rises and meets it instead) you don't get to extract that gravitational potential energy. It's as simple as that.

                    And you're being pretty blithe invoking tides. Since tidal forces fall of like 1/r^3, you'd need a monst
                    • If the planet never falls into the star (the star rises and meets it instead) you don't get to extract that gravitational potential energy..

                      And you're being pretty blithe invoking tides. Since tidal forces fall of like 1/r^3, you'd need a monster of a planet to induce significant tides in the star.

                      Well, which is it? When you say that "the star rises and meets it", you seem to be describing the inducement of a tidal bulge or Roche lobe. You then complain that I am invoking a tidal bulge. And while you sa

        • 2) Um, no. When a star gets to Fe (and only very large stars do), it makes a nice little explosion adn we enrich the interstellar medium. Which is where pretty much all of the "metals" (anything heavier than helium, according to astrophysicsists) in your body, Earth, the Sun, etc. come from. So the question about metal-rich stars isn't "are they producing the metals", they would have had to leave the main sequence for one thing. The question is did the cloud that formed them have an more metals than the ave
          • Actually yes you can fuse iron .. where do you think all the heavier elements came from?

            .. However, fusing Iron takes more energy than it releases! THIS is the reason stars die when they hit the Iron stage if they get that far at all.

            Whats the arguement here anyways? the boost of fuel from the planet impact is meaningless, you have all well established that.

            Now, THINK about it! - it was the momentum of the impact that caused the brightening, not increased fusion. If the momentum itself didnt incre

            • Re:A Couple Thoughts/questions (Score:4, Informative)

              by barawn ( 25691 ) on Thursday September 18, 2003 @10:12AM (#6994183) Homepage
              No - you don't fuse iron. You neutron-stuff them. During the supernova, the outbound shock wave carries so much energy (and neutrinos) that neutrons are literally "shoved" into nuclei. You get ridiculous things like iron with hundreds of neutrons, which then decay down into normal elements by alpha emission and beta decay. This is r-process stellar nucleosynthesis. (There's also s-process stellar nucleosynthesis, which is also neutron stuffing, but on a much longer timescale. Essentially everything past iron is formed by r-process stellar nucleosynthesis. Check Carroll & Ostlie pp 527-528 for more info.

              Stars die when they hit the iron stage because they can generate no outward pressure from fusing iron. They can't even fuse iron at all! It's actually a really complex procedure - basically, the iron starts to lose all of its electrons (from proton capture and other mechanisms) so the core rapidly loses electron degeneracy pressure, which is what was (briefly) supporting it. The inner core collapses very uniformly to a little neutron star, and the outer core decouples from the inner core, and the outer core rushes inwards at extreme velocities. The collision of the two is one of many explosions in a supernova. (Again, see Carroll & Ostlie's section on the Death of Massive Stars)

              Anyway, the fuel isn't insignificant depending on what stage the star is in, and also depending on how fast the planet's orbit would decay once it's inside the photosphere. If it meets with the star's core without significantly losing mass, that could cause a VERY large brightening. Functionally it's equivalent to a nova, or the pulsing of Wolf-Rayet stars (without the mass shell shielding it).

          • Re:A Couple Thoughts/questions (Score:4, Informative)

            by CheshireCatCO ( 185193 ) on Thursday September 18, 2003 @11:37AM (#6995029) Homepage

            Depends on the kind of star. The core of the star - that is, the "dense" part -

            In this case, it's an F-class star. And you missed my point entirely, which was that if the star can convect the planet's hydrogen into the shell-burning zone, it can damn well convect its own hydrogren reserves down there, which are vastly in excess of what the planet could provide. So the star should never notice the miniscule addition of the planet's hydrogen.

            This is all theory, of course, but unfortunately, theory doesn't quite bear out the "hydrogen compounds = gas giant planet cores".

            See, that's where you're amazingly wrong. Let's review out giant planets, shall we? (If you want, I suggest you crack open Protostars and Planets IV; it's always good to actually do a bit of research.)

            Jupiter May or may not have a core in the first place. If it does, it's at most around 10 Earth-masses (maybe as high as 15, but that's at the outer edge of the error bars). Mostly, it'll be hydrogen compounds with some rock and metal (real metals, not in the astrophysical sense). You need that core in standard formation models before you can accrete the hydrogen and helium gas. The metallic hydrogen is a layer right above the core, not the core itself.

            Saturn Has a core, around 10-15 Earth-masses. Same as Jupiter in composition. This is easier to work out in theory because the equation of state is better understood for the interior pressures within Saturn. (Jupiter's higher pressures make things more dicey.)

            Uranus and Neptune Definately have cores. Also icey with a bit of metals and rock thrown in. Again, need said core to hold on to the gas in the first place. Cores are pretty well constrained in size at around 15 Earth-masses in both planets. Given that both planets are around 18 Earth-masses in size, you bet your ass that this means that they are both mostly core. In fact, it's this that has lead some leading researchers to dub them "ice giants", in contrast to Jupiter and Saturn, the "gas giants."

            I don't know where you got your "facts", but they're pretty much uniformly wrong. See Wuchterl et al. in P&P IV for more details on constraints on the present structures of these planets.

            • I agree that the BBC article is woefully short of details, like how much additional energy was released, and the like. But before rejecting the conclusion out of hand, keep in mind that we're not entirely sure about a lot of "core" facts about our own planetary neighbors:

              You need that core in standard formation models before you can accrete the hydrogen and helium gas.

              According to this space.com article from 2001 [space.com], extrasolar gas giants are throwing doubt on the "accretion" model of planet formation:

              I
              • It's worth noting that Alan Boss is, as far as I've seen, the only one who believes his theory. (The press will report any theory, no matter how speculative and poorly received by the general planetary community.) Even Alan refers to himself a heretic (in a light-hearted way) for espousing it. For one thing, Alan's mechanism would result in eccentric giant planets (zero eccentricity is as likely as anything else). But our giant planets are all in fairly circular orbits. This seems unlikely. Also, we
            • Let's review out giant planets, shall we?
              Given that both planets are around 18 Earth-masses

              First off, last time I checked, Uranus is 14.5 M_earth, not 18 (Neptune is 18 M_earth: even Google can tell you that: search for "mass of Uranus / mass of the Earth" and "mass of Neptune / mass of the Earth") , so it's core BETTER be less than 15 M_earth. Don't jump at someone about checking facts when you make a mistake like that.

              Anyway looks like I got the core masses for Uranus and Neptune from dated sources,
              • "mass of Neptune / mass of the Earth"

                Hey, that doesn't work in Google. What the heck? Neptune's not good enough for Google?

                Anyway, Neptune's really 17.1 M_earth - I used 18 because it was 18 in the parent post, and didn't stop to remember - I knew it sounded "close".
              • If you want the planetary parameters, why not go to the obvious source: NASA. http://ssd.jpl.nasa.gov, Google not needed. Glad you're actually doing some research before speaking, anyway. And, yeah, yer right, Uranus and Neptune are nearer 14.7 and 17 Earth-masses. I was doing the numbers from memory, sorry. But all that means is that both ice giants are even more core than I asserted earlier, meaning you've just supported my point that what you were spouting about the planets' cores was total bull.

                (T
                • If you want the planetary parameters, why not go to the obvious source:

                  Because Google gave it to me in a few seconds? If I really wanted to get it from a "more scientific" source, I've got plenty of other sources within arm's reach.


                  It is NOT possible that this little hydrogen could cause an increase of a factor of 100 in the brightness. There is always plenty of hydrogen left over in the overlying layers.

                  What I said was that if the planet reaches the core, it could cause something akin to a nova. I
    • To answer my own question (woo for Google!), the star has brightened from about magnitude 11 or 12 to about 6.5. That's around 5 magnitudes of brightening, or a factor of 100 in the overall luminosity. AAVSO's site talks about it: http://www.aavso.org/vstar/vsots/1202.shtml

      I have to say, I'll be interested to see their paper when it hits press, but I'm really skeptical.
  • Planets taste like chicken!

  • hmmm (Score:4, Informative)

    by GypC ( 7592 ) on Wednesday September 17, 2003 @04:26PM (#6988736) Homepage Journal

    If it's 20,000 LY away it didn't brighten 3 times last year (that we know of)... rather it brightened 3 times in one year approximately 20,000 years ago.

  • Good Joke (Score:3, Funny)

    by gnovos ( 447128 ) <gnovos@ c h i p p e d . net> on Wednesday September 17, 2003 @04:44PM (#6988890) Homepage Journal
    I just know there is a good joke in there *somewhere* with gas-guzzling, solar power, and SUVs... I just can't get my mind around it yet...

  • Maybe... (Score:3, Funny)

    by mraymer ( 516227 ) <mraymer@nOsPaM.centurytel.net> on Thursday September 18, 2003 @01:05AM (#6991776) Homepage Journal
    The increase in the brightness of V838 Monocerotis is due to some interstellar war!

    Kick ass. Now that's why we need a space program!

    • If that war involves throwing gas giants in to stars, I thinking we'd best lay low for a while. Maybe we can pick up some sweet artifacts after they anihilate each other, though.

  • Unlikely? (Score:4, Interesting)

    by Alsee ( 515537 ) on Thursday September 18, 2003 @07:07AM (#6992928) Homepage
    It's a facinating theory, but there's a huge problem with it. Planetary orbits are highly unstable unless they are pretty widely spaced. It is therefore pretty much impossible that there were THREE planets anywhere near the same distance away from the sun.

    Seeing it happen to three different stars in one year, OK. Seeing it happen three times to one star over thousands or millions of years, OK. But there's no was a single star ate 3 planets in a single year without some HUGE outside influence disrupting the orbits.

    If the theory is right then it is of secondary interest, and whatever triggered the triple event is probably far more important and interesting.

    -
  • And remember my sun, if you're going to eat a gas-giant, please don't forget the Bean-O. Solar wind can be most disruptive.

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