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Galactic Traffic Patterns 81

Posted by Hemos
eldavojohn writes "Using Hubble, researchers have noticed traffic patterns of stars within our own galaxy. From the article, 'Researchers analyzed 47 Tucanae, the second largest cluster in the Milky Way's galactic neighborhood, and determined the cluster sorts out stars according to their masses. Due to the associated gravitational pull, heavier stars slow down and sink to the cluster's core, while lighter stars pick up speed and zip out to the cluster's periphery.' There is speculation that these movements of stars — although tiny — can have significant implications and possibly result in mass segregation."
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Galactic Traffic Patterns

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  • I fail to see how this is more significant than "rocks sink and beachballs float"? :)
    • by quigonn (80360)
      It shows that this is also true for heavy masses, probably? Quite obvious, but you won't believe how much scientific work with obvious results is done (yes, bash me for that, Karl-Popper-fanboys).
    • by Oztun (111934) on Monday October 30, 2006 @11:05AM (#16641931)
      Except in this case the rocks sink slow and the beachballs drop like a rock.

      -Please don't take this comment seriously.
      • by Barryke (772876)
        1) its not funny
        2) and not true
        3) and not sarcastic.
        4) the last line of your post suggests that you are a karma hooker.

        You just dont make sense.
        Beachballs (light stars) get swong out, and rocks (heavy stars) *do* get sucked in.

        Imagine a big roulette table without an outside border or obstacles inside.
        Trow in a light ball, it will spin longer.
        Trow in a heavy ball, it will drop sooner.
        Use constant velocity to trow them in orbit, and not so hard that one or the other will touch the outside in their first orbit
        • by Huggs (864763)
          Apparently in reading the last line of that post, you missed the point of the last line of that post.
    • Better one (from my second prize ribbon-winning science fair project in 2nd grade): Why does a ship float and a potato sink?
    • If you think about it a while you can see the problem - these stars are in orbit, so they should fall at all. Essentially, the stars are being sorted by mass when they should be just going around in circles...
      • If you think about it a while you can see the problem - these stars are in orbit, so they should fall at all. Essentially, the stars are being sorted by mass when they should be just going around in circles...

        Well, that's the obvious expectation if you consider only the interactions between each orbiting star and the center of mass of the galaxy; but their actual motion is a lot more complicated because the you've really got a bunch of non-uniformly distributed objects attracting each other, which is why (b

    • It's needed for Samantha Carter's stellar drift calculations.
    • Re:I fail to see ... (Score:5, Interesting)

      by Artifakt (700173) on Monday October 30, 2006 @01:30PM (#16644039)
      Rocks sink and beachballs float because of differing densities, not differing masses.
      Here, we're looking at stars of different sizes and masses. There aren't some stars made mostly from silicates and iron oxides, while other stars are hollow plastic shells with slightly compressed air cores, or anything like that. A big red giant star may weigh 5x the mass of our sun, but be hundreds or thousands of times more voluminous, so the density as a whole object is actually much lower than a sun sized star.
            Also, rocks sink in water. In a pool of mercury. both typical rocks and typical beachballs float. In vaccuum, near a gravitational source, everything that has mass is accelerated at the same rate, and densities really don't matter. Density affets falling objects if there's a drag, like there is falling through air. The space between stars is generally a near perfect vaccuum.
            It's significant, because simple, standard physics explanations of sorting by density, type of material, or mass don't entirely explain this. Instead, there are probably other factors such as transfer of momentum between whole groups of stars, perhaps also to gas clouds or something, and maybe even modifying factors such as light pressure or angular momentum-linear momentum exchanges which are in turn affected by such unexpected things as the stars involved's relative surface areas or diameters.
            The article talks about slingshot effects. Small stars can be slingshotted a lot faster by the same force that will only moderately accelerate large ones. This in turn means their orbit around the galactic core may even become a parabola or hyperbola, so that any given encounter sometimes becomes their last pass through the cluster. Larger stars get sped up and slowed down, but seldom by all that much, so they tend to keep returning to the cluster.
            Sorting out which of these factors, and possibly others, are important and which are trivial is why the people studying this actually have to learn some math.
  • by k4_pacific (736911) <k4_pacific@noSpaM.yahoo.com> on Monday October 30, 2006 @10:55AM (#16641805) Homepage Journal
    "...and possibly result in mass segregation."

    If this keeps up, the stars are gonna be marching on Washington, demanding their equal rights. I have a dream, that someday, all stars will be judged not be mass, but by the content of their cores.

    • These NASCAR dads, playing the race card...
    • by hcob$ (766699)
      Hey, it's all the Republican's Fault. Anything to do with segregation is always their fault!
      • by Gospodin (547743)

        Of course! (Even though Democrats were the biggest supporters of segregation at the time. You're only allowed to whisper this.)

        • Re: (Score:3, Informative)

          by zentinal (602572)
          I'd say that today's Democrats have about as much in common with Democrats then (Reconstruction through the late 1950's) as today's Republicans have in common with Abe Lincoln's Republican party.
    • > someday, all stars will be judged not be mass, but by the content of their cores

      The content of a star's core is determined by its mass. Every star starts out with nothing but hydrogen and has to manufacture everything else. Larger stars burn hotter and can fuse heavier atoms. Some stars explode, spew out stellar matter, and become smaller stars, but this is really their own damn fault. So mass really is the main factor by which stars ought to be segregated. If you think it unfair, build your own univer
  • doesn't the summary defy conservation of energy? I thought they should speed up if they get closer and slow down if they get further away like an ice skater.
    • by photontaker (1020241) on Monday October 30, 2006 @10:59AM (#16641855)
      It's actually an equiparition of energy thing. Due to all of the gravitational interactions that occur in the cluster, all of the stars should have the same total energy (potential + kinetic). Therefore, at a given area in the cluster, the heavier stars (which are around .80 solar masses) should be moving slower than the lighter stars (which are .2 to .4 solar masses). The amazing thing is that they were able to determine this by measuring 1/100th of a pixel shifts in Hubble images. Needless to say, it's hard to do astrometry that precisely.
      • by beckerist (985855)
        and not only given the problems Hubble has had in its lifetime, it's also hard to take this 'evidence' as credible given the nature of the measurements!

        I'll give an example: Give a thumbs up, and stick your arm out in front of you as far as it will go. Close your right eye and notice where your thumb is against the background. Now close your left, open your right and do the same thing. Notice your thumb moved relative to what's behind it?

        ...now imagine this with your "eyes" being replaced by the earth o
        • Well, this is what I do for my research, so I actually do know what I'm talking about.

          The basic idea is that we know the shape of the point spread function of hubble extremely well. Since we do know that shape, it's fairly easy to do a cross-colloration and find positions to much better than single-pixel accuracy. Even from the ground it's pretty easy to get positions better than 1/10 of a pixel.

          The thumb analogy used above is called parallax (which is often used to determine the distance to nearby stars)
  • by Rob T Firefly (844560) on Monday October 30, 2006 @10:56AM (#16641823) Homepage Journal
    All this talk of galactic traffic, and not one mention of the hyperspace bypass. [wikipedia.org]
  • Spock, (Score:5, Funny)

    by crazyjeremy (857410) * on Monday October 30, 2006 @10:57AM (#16641837) Homepage Journal
    They ... keep ... going ... around ... in ... circles.
  • by onion2k (203094) on Monday October 30, 2006 @11:02AM (#16641887) Homepage
    This is interesting. From my hopelessly and woefully inadequate understanding of celestial mechanics I would guess this must be due to the stars rotating around some huge mass in the centre, right? A black hole or similar? Without that in place wouldn't the stars interact with one another and eventually end up a horribly chaotic mess? The article doesn't say.
    • by AltGrendel (175092) <ag-slashdot AT exit0 DOT us> on Monday October 30, 2006 @11:26AM (#16642219) Homepage
      You aren't the first one to think of this. From wikipedia [wikipedia.org], "The galactic center harbours a compact object of very large mass (named Sagittarius A*), strongly suspected to be a supermassive black hole. Most galaxies are believed to have a supermassive black hole at their center."
      • Actually, I don't believe you need a massive body at the center of the cluster to cause this to happen. Dynamical friction (due to the gravitational interactions between the stars) could have this effect, with small stars slingshotting off large stars, causing the large stars to loose energy.

    • by finity (535067)
      In some systems, multiple large objects rotate around a shared center of mass. One example is the binar star (http://en.wikipedia.org/wiki/Binary_star [wikipedia.org]) type of system. I think these things can contain more than two elements... Don't quote me on that though.
      • In some systems, multiple large objects rotate around a shared center of mass.


        Well, actually, that's how orbits work in general, its just in some cases, one object is massive enough that the "shared center of mass" is not far from the center of mass of the massive object.
    • by Azathfeld (725855)
      It does, to some, imply a massive object at the center of the galaxy, but it doesn't require it. Random accretions of stars into one giant cluster could exert similar gravitational effects without any single object for the dance to happen around. In fact, this lends some support to that hypothesis, as normal galactic rotation could tend to pull massive stars toward the center, creating a self-perpetuating cycle as those stars add to the centralized mass of the galaxy.
    • by kalidasa (577403)

      Yes and no. As it happens, we think that most (if not all) galaxies do have massive objects at their cores - but the question is, whether that object was what caused the galaxy to form, or whether it was a byproduct of some other process (for instance, I can see how mass segregation would eventually lead to the formation of a black hole at the core of a galaxy). As someone else has pointed out, in a complex system, the objects can orbit a common center of gravity that is not associated with any one massive

    • To respond to a number of responses, this article is actually about globular clusters [wikipedia.org], not galaxies. Some globular clusters may have black holes at their cores, but others almost certainly do not (as I understand it). It is not neccessary that there be a huge mass in the center. When you have a large collection of objects close together they can act (very roughly) as if their combined mass were in the middle and they were orbiting that - this description is highly simplified, but it illustrates how a cen
    • by TMB (70166)
      The stars orbiting around the centre of mass of the system is "the stars interact[ing] with one another".

      [TMB]
  • How much money did they waste on THIS study? All they had to do is ask the Vogons, who have many reports on file concerning galactic traffic patterns (never mind that you have to file the requests at a planet 18 light years away, and that the files are located in cabinets in mynock-infested rooms).
  • by Dausha (546002)
    "while lighter stars pick up speed and zip out to the cluster's periphery"

    Where's a cop when you need one? I also would like to take offense to the statement that older, fatter stars move more slowly and drop down. This article is just begging for an intergalactic lawsuit.
  • When I saw the title, I thought this article was going to tell is when Adama and crew find Earth! Sucks to be hooked on a TV show. FRACK!
  • by Chacham (981)
    This stuff rocks so hard, is has stars going around my head. That such light objects, are so heavy, shows the gravity of the whole thing, yet it makes music better than a gala xylophonic experience, and makes us realize that noone would have sold our system for anything else.
  • I hate when you're traveling down a spiral arm at 465m/s and you have to SLAM on the brakes because a bunch of systems have slowed down to a crawl to gawk at some dumbass who went nova. Geez, people, I've got sectors to see, and a job interview seven light-hours away!
  • So when will Battlestar Galactica reach Earth? Last I heard there were reports of battlestars and basestars zipping all over the commuter lane.
  • by Kamiza Ikioi (893310) on Monday October 30, 2006 @11:53AM (#16642569) Homepage
    If heavy objects sink to the core, and lighter ones speed up, and go to the outer rim... do galaxies of galaxies behave the same way? And by that thinking, is the universe really expanding, or are we just moving towards the outer rim being a very large section of lighter galaxies (and we just appear to be expanding because behind us are heavier objects accelerating slower, stopped, or accelerating back into the core, and lighter objects are moving faster in front of us as we are all just moving on an outward spiral, thus giving the appearance of a universe that is spreading apart)?

    And, if that's so, what would "THE core" be like. Hmmm, black hole not of one star but of entire galaxies?

    Which begs the question, is there enough gravitational pull at a hypothetical core of all cores to hold the universe together like a giant counter weight on a pendulum, with fluctuations between expansions and collapses? (Never mind if 'Sha Ka Ree' is really there if it has the mass of 1 million Milky Ways, heh.)

    IANA astronomer, astrophysicist, etc. Just curious because from what I read, as go moons, so go solar systems, so go galaxies, so goes the universe.
    • by archen (447353)
      According to current observations of the universe (what was said in "A Brief History of Time" anyway) that isn't so. It's been found that the spectral shift of galaxies shows that the father away a galaxy is, the faster it is also moving away - which means nothing is behind us just accelerating slower in the same direction as us. If you put a bunch of dots on a balloon and blow it up; that's basically what the universe is doing.

      I'm guessing that assumes that we can also see everything, which we may possib
    • by Shotgun (30919)
      We really need an astrophysicist here.

      Why the dichotomy? Why must everything either be blown apart forever, or eventually everything sucked back in? Why can the Big Bang/Big Collapse, instead be Big Bang/Not Quite as Big Collapse, as in a damped oscillation? Some material being lost each period, resulting in a smaller bang until the process just wears itself out?

      I'm positive that someone smarter that me has postulated such a circumstance, but I've never heard of it. It's always either open or closed, ne
      • You should thank your lucky star that you exist so you
        can even contemplate such questions.

        Personnally, as SpaceLifeForm, I have seen no big bang, nor
        any collapse. The Universe just exists, is infinite, and
        will always exist. Everything else that points to expansion
        *or* collapse is just an illusion, physics to confuse the
        observer.
      • by TMB (70166)
        What you're refering to is the "critical universe", which was what most astrophysicists used to believe we lived in because it's so much more elegant (and people had thought that it was a firm prediction of inflation because no one really thought that the cosmological constant wasn't zero). But it turns out that the universe is stranger...

        [TMB]
    • Another reply pointed out that galaxies behind us are moving away as well. This can be looked at another way though. In order for this effect to happen on the largest scales of the universe, all galaxies must be gravitationally interacting. However, the distances involved are often too great to make such interactions significant. On smaller scales, such as clusters of galaxies, these gravitational interactions are significant, so it is concievable that something similar to what's in the article could occ

    • by TMB (70166)
      Cute idea, but it doesn't work. Mass segregation only happens when the objects have many many many close interactions with their neighbours. They exchange energy in each interaction, and the equilibrium situation after many interactions is an equipartition of energy - each object has the same energy. Just looking at the kinetic energy, KE = m v^2, so a higher mass object has to have a lower velocity in order to have the same energy, which leads to mass segregation.

      But you only reach equipartition after many
  • I guess pretty soon, we'll have to start bussing stars around to get an equal mix of heavy and light stars. Otherwise, the galactic central cores gonna be all fat, old stars griping about how they don't get cosmic incidents like they used to in the old days and all these young stars with their loud music and the dancing and the glavin. oh, hey!
  • Will someone please tell me which Dept. this article is from? Shouldn't it be from the don't-tailgate-Starbuck Dept. or something?
  • To reply to the previous comment, mass segregation should also occur in clusters of galaxies, especially the big rich clusters. Indeed, you often see supermassive elliptical galaxies in the center of clusters. The problem there is that the idea of equiparition of energy requires lots of 3-body gravitational interactions to equalize the energy of all the various objects. In globular clusters, this happens on short timescales (the timescale might be only 500 million years. :) ) In galactic clusters, you m
  • Does this have any implications on the density of mass? When I think of things spinning around a center (e.g., the center of a galaxy), I think of a centrifuge. In a centrifuge, the matter is segregated by density (denser objects move to the outside). So, is it possible then to argue that the lighter stars (although lighter) are more dense than the heavier stars? I guess it depends on the magnitudes of the various forces. Everything is on such a scale that I can't even guess what forces are dominant; h
  • Are binary systems allowed to use the starpool lane?
    • by boisepunk (764513)
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  • I'm not sure this should come as much of a surprise, given that this has been predicted by dynamical theorey.

    It's nice that it's been observed though.

  • Can't be any worse than the 405 in LA.

I'd rather be led to hell than managed to heavan.

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