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Space Science

Anomalous Pulsar In Binary System Stymies Theorists 53

Science Daily has word of a millisecond pulsar in the wrong kind of binary system that has astronomers scratching their heads. According to current models of pulsar evolution, such a system should have no way to develop. The pulsar J1903+0327, which rotates 465 times per second, seems to be in a highly elongated orbit around a Sun-like star. Quoting: "Astronomers think most millisecond pulsars are sped up by material falling onto them from a companion star. This requires the pulsar to be in a tight orbit around its companion that becomes more and more circular with time. The orbits of some millisecond pulsars are the most perfect circles in the Universe, so the elongated orbit of the new pulsar is a mystery."
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Anomalous Pulsar In Binary System Stymies Theorists

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  • by argent ( 18001 ) <peter.slashdot@2006@taronga@com> on Friday May 16, 2008 @02:03PM (#23437198) Homepage Journal
    See what happens when real physicists write SF [wikipedia.org]!
  • Perhaps the pulsar is closely paired with another small star and the pair has just be captured by a larger star. Wonders never cease!
    • The pulsar could be paired with a black hole, or another neutron star which is not pointed our way. The visible star could have been captured by the pair, forming a triple.
    • by Gat0r30y ( 957941 ) on Friday May 16, 2008 @02:28PM (#23437692) Homepage Journal
      The article discusses this option, and actually finds it the most satisfying explanation. -

      A third scenario says the pulsar may be part of a triple, not a double, star system. In this case, the pulsar's 95-day orbit is around a neutron star or white dwarf, not the Sun-like star seen in the infrared image. The Sun-like star would then be in a more-distant orbit around the pulsar and its close companion
      Most certainly a quite intriguing possibility.
  • Aha! (Score:4, Funny)

    by loftwyr ( 36717 ) on Friday May 16, 2008 @02:15PM (#23437464)
    This will be the iron clad proof of Creationism! Only (insert your favourite supreme being here) could have put such an anomaly there!

    All hail (insert your favourite supreme being here)!
    • Re: (Score:3, Funny)

      by argent ( 18001 )
      The FSM hates touching pulsars with his noodly appendage... he gets gravel-burns like you wouldn't believe.
  • The pulsar was captured by the star and is now in a elongated, possibly unstable and decaying, orbit.

    Oh, wait, that is too simple an explanation.
    • How do you capture a pulsar? You have to shed energy somehow. I suppose binary capture is possible, but that seems like the only real option here.
      • Not at all. If one is loose, all you need is a sufficiently massive body, and the right vector of approach. Obviously if the pulsar is moving at an extreme relative velocity, or if it is more massive than the object its passing, it is unlikely to fall into orbit.

        But anything can be pulled into a gravitational orbit if the central body is massive enough. Most pulsars aren't more than one or 2 solar masses, and stars can generally exist up to around 5 solar masses...Bigger than that, and you get a black hole.
        • Re:A simple answer (Score:4, Informative)

          by CheshireCatCO ( 185193 ) on Friday May 16, 2008 @03:07PM (#23438326) Homepage
          What the heck are you talking about? If you have a positive relative energy before the encounter (which you must if you start not in orbit), you must dissipate energy in order to get captured into orbit (which requires a negative relative energy). The masses of the bodies involved do not change that simple physics.
          • Gravitational attraction is proportional to mass (and distance). Assuming that the pulsar is fairly typical, that means its between 1 and 2 solar masses; couple mass and velocity and you get momentum, which, unless I am mistaken, is the more common term for the energy you are talking about.

            The central body must be able to exert a force great enough to overcome the momentum of the unattached body. For it to have a chance of doing this, it must necessarily be more massive than the pulsar, probably substantial
            • Re: (Score:3, Insightful)

              Arg, no. No, no, and no.

              Momentum is not energy. They are separate quantities and are conserved separately. The mass of the star is, as I stated earlier, irrelevant. When you have two bodies, the bind energy DOES NOT CHANGE during an interaction without some other dissipation. Gravity is a conservative force.

              Look, I appreciate that you're throwing ideas out there, but this is pretty basic physics that we have a good handle on. If you don't believe me (which is fine!), look some of this stuff up for your
              • Re: (Score:3, Interesting)

                I'm trying to figure out what other energy would apply. It's more just an honest question (my physics is obviously more of the terrestrial sort). Would something have to shed mass or slam into an orbiting body or something similar, in order to be bound?

                • There's only one energy here. You are, I think, confusing energy with momentum. These are very different quantities.

                  Look, here's the energy of two gravitationally interacting bodies:

                  E = 1/2 (m1 v1^2 + m2 v2^2) - G m1 m1/r

                  For gravitationally bound bodies (i.e., in orbit), E0. (E=0 basically never happens for statistical reasons.)

                  Now, gravitation is a conservative force (never mind how you prove that for now), so E does not change during an interaction. v1 and v2 might increases as r decreases, by E does
                  • Gah, I missed the fact that < gets consumed by Slashdot's formatting. Everywhere that there's an "E0" in the last post, assume that it's "E<0", please. :-)
                    • Could a supernova on entry into the yellow star's system have caused the right amount of force?

                      I.e., The pulsar (and invisible twin) are traveling towards a star (or vice versa, depending on POV). It supernovas as they are passing by, slowing the twin system just enough to pick up all the debris from the newborn system in an elliptical orbit, or vice versa. The orbit is far enough away from the pulsar or newborn system so as to allow the newborn system to develop naturally into another star system. The tr

                    • I'm not sure I followed all of that, but an SN could, I suppose, in theory provide the braking force needed to shed some of the energy. But it's extremely unlikely, the timing would have to be awfully precise.

                      The triple-star system idea seems a lot more likely.
                    • Yeah, I wasn't too concise with my description. Seems like you got it though.

                      As to the likelihood of it happening, though, we (the human race) have seen stranger astronomic coincidents.

                    • Not sure we've seen strange coincidences in the sky, but I'd say that we humans may be more unlikely. :-)
                  • by Cyberax ( 705495 )
                    Maybe, it was a binary system which captured a neutron star, ejecting one companion in the process.

                    It's possible, but very unlikely.
                    • Yeah, that's the three-body problem. Of all the capture scenarios, that seems the most likely. However, it still seems unlikely since a millisecond pulsar would be close to its companion and therefore hard to strip away.
                    • Considering the masses of the stars involved, I'd say that the pulsar captured one member of an approaching pair of stars, and ejected the other. However, this doesn't explain why the pulsar is flickering at a millisecond rate. A young pulsar (like the one in the Crab Nebula) can be expected to pulse that fast, but if it was young, then where is the nebula (supernova remnant expanding gas cloud)? If it is older, then it can only (so far as we know) flicker at millisecond rate by getting a boost (typicall
                    • by Cyberax ( 705495 )
                      How about a double-supernova? It can, in theory, eject a pulsar with a pretty good proper velocity.

                      BTW, I'm not an astrophysicist, but right now I'm running different variants of capture scenarios on my cluster.
                    • A double-super nova?

                      A single SN can eject a pulsar at high speeds (this isn't even just a theory, we observe them moving pretty fast so it's a pretty reasonable conclusions :-), but remember that the pulsar started out inside the star, thus felt a lot of force. As you get farther away, the force falls off as 1/r^2 (one would think, perhaps a bit faster). At reasonable astronomical distances, it probably wouldn't be very big. Perhaps juuust enough to switch a pass into a capture, though, it it was marginal
                  • by lgw ( 121541 )
                    If the neutron star is passing close enough to the companion star to swallow chucks of it, there's your "other process". This is the exact mechanism by which these orbits become so circular over time. This pair of stars may simply be at the start of the process - statisticlly unlikely, but then this observation is statistically rare, so why not?
                • Re: (Score:1, Informative)

                  by sp332 ( 781207 )
                  Here, I know this is a little backward, but it's cool and it illustrates what is conserved. Try it yourself: http://isthis4real.com/orbit.xml [isthis4real.com]
                  • Re: (Score:1, Informative)

                    by Anonymous Coward

                    Here, I know this is a little backward, but it's cool and it illustrates what is conserved. Try it yourself: http://isthis4real.com/orbit.xml [isthis4real.com]

                    It's also wrong. The creationist propaganda that comes with it is exactly why I get pissed off at creationists and ID people. They try to use flawed scientific arguments that sounds right to the uneducated.

                    It ignores gravitational interactions with other bodies in the solar system, ignores friction with the atmosphere (although it does include some type of friction when the two bodies are actually touching one another) when you start at ground level, and it doesn't allow you to move the "outer space"

                • Would something have to shed mass or slam into an orbiting body or something similar, in order to be bound?

                  That could work, but a more reasonable process is that a binary (or multiple) star system interacted with the pulsar system, then the excess energy could be carried away by the stars not captured. Or a single star could displace another star (or perhaps even a large planet) that was already there. In most of the galaxy it is very rare for star systems to come close enough to interact like that though. It is much more likely that the pulsar was part of a multiple star system when it formed, and the syste

      • Well, first it could be a small pulsar and a large yellow star. And, if they have a low relative velocity, then the relative energy would be slow.

        And, the orbit may not be stable. It could be slowly collapsing.
        • Re: (Score:3, Informative)

          You miss the point. They cannot be in orbit if they started out not in orbit UNLESS there is energy lost during the capturing. This is basic physics stemming for binding energies.

          With planets, you can dissipate energy this with atmospheric drag, firing rockets (if you're a spacecraft), or three-body capture*. Only the last of these works with stars, and that's a dubious proposition since the millisecond pulsar would probably have been pretty close to its partner before the capture making it hard to strip
          • Re: (Score:3, Informative)

            by Scott Ransom ( 6419 )
            You are correct that you need a dissipation mechanism to capture a pulsar into a new orbit.

            For this system, assuming it started out in the dense stellar environment in a globular cluster, exchange encounters between multiple stars (3 or 4, i.e. single-binary or binary-binary) can provide the dissipation since the lowest mass stars (i.e. not the pulsar) tend to get energy boosts and are then ejected from the encounter. Alternatively, as you suggest, tides during a very close encounter can lead to a capture.
            • Yeah, I would have thought starting it as a 3-body system would work better.

              Tides wouldn't work very well I shouldn't think. There's just not enough dissipation at the required rate I'm pretty sure.
            • I'm way the hell out of my league here, but the xscreensaver "attraction" does a pretty good job of showing you how orbits are attained with 3 separate masses.
      • Re: (Score:3, Informative)

        by Scott Ransom ( 6419 )
        For the triple scenario you never have to capture a pulsar. You only have to have the triple stellar system survive the supernova that created the neutron star (i.e. pulsars are neutron stars) and then subsequently, one of the other stars has to "recycle" the neutron star into a millisecond pulsar via accretion. The recycling process happens when a "normal" main-sequence star evolves into a red giant and dumps its outer envelope into a disk around a companion neutron star. When recycling is finished, you
        • Yeah, a triple-system definitely struck me as more likely than capture. I just didn't mention it because it wasn't what was being suggested here. :-)
    • by Tango42 ( 662363 )
      Did you even read the summary? The same mechanism that made the pulsar rotate so fast should have circularised the orbit. Getting the pulsar into a highly eccentric orbit isn't hard, but getting it rotating that fast in one is.
  • Everyone is wrong! It is the mother ship calling! The signal has finally arrived and been detected! Everyone head to the embarkation points and prepare to depart!

    This was suppose to have back on 12/31/2000 at midnight but for some reason the signal was not detected at that time. The time is now upon us! Finally!
  • If it only rotates 465 times per second, wouldn't that just make it a "centisecond" pulsar?  Wouldn't it have to rotate at least a thousand times per second to be a millisecond?

    • by phliar ( 87116 )
      If it rotates 465 times a second, the period of its rotation is 2.15 milliseconds. I think 2.15 is closer to 1 than to 10... at least in some states!
  • According to accretion theory, there's no way Venus could have formed with its spin in the opposite direction of the solar system. The prevailing theory is that a protoplanet smashed into it and radically changed its spin, possibly multiple times. Same goes for Uranus, which spins sideways, rather than backwards.

    It's entirely possible that this pulsar formed in the usual way, but some interaction with a very massive object pulled it out of its pristine circular orbit. Given how these orbits stabilize the
  • There's no particular reason why a pulsar cannot 'spin up' in an elongated orbit. It would take longer though, and it would need to be timed in such a way that it's material transfer events maintain the orbit, rather than 'flattening' it out.

    Or, perhaps more likely, an especially energetic eruption pushed it out of a formerly 'flattened' orbit.

"No, no, I don't mind being called the smartest man in the world. I just wish it wasn't this one." -- Adrian Veidt/Ozymandias, WATCHMEN