Slashdot Mirror

← Back to Stories (view on slashdot.org)

US Lab Models Galaxy Cluster Merger

Posted by samzenpus on from the we're-going-to-need-more-ram dept.

astroengine writes "The scales are mind-boggling and the physics is cutting edge, so how do you go about simulating the collision of two galactic clusters? Using some of the most powerful computers in the world, researchers at Argonne National Laboratory, the Flash Center at the University of Chicago and the Harvard-Smithsonian Center for Astrophysics have done just that."

64 of 89 comments (clear)

  1. Does this qualify as a big bang? by ctmurray · · Score: 3, Funny

    When two such large object collide in outerspace does it make any noise?

    1. Re:Does this qualify as a big bang? by DarkKnightRadick · · Score: 1

      Only if the irradiation of countless barren worlds has a sound.

      --
      "There is a way that seems right to a man, but its end is the way of death." Proverbs 16:25 (NKJV)
    2. Re:Does this qualify as a big bang? by Mitchell314 · · Score: 1

      It's a small "ping" sound, with a slight echo.

      --
      I read TFA and all I got was this lousy cookie
    3. Re:Does this qualify as a big bang? by lavagolemking · · Score: 4, Informative

      No. Sound is the vibration of air molecules, so when you speak or drop something, it creates compression waves that travel through the air and vibrate your eardrum, which in turn creates waves in the fluid of your cochlea that stimulate hair cells connected to the acoustic nerve. Since outer space has (almost) no air, these waves have no medium on which to travel, and sound as we know it does not happen.

    4. Re:Does this qualify as a big bang? by trashpickinman · · Score: 5, Funny

      Whoosh... Thats the sound of a joke going over your head.

    5. Re:Does this qualify as a big bang? by Sean_Inconsequential · · Score: 1

      With the distances between stars in a galaxy, it is unlikely that the stars in those galaxies will actually collide. Though a galactic merger will cause rapid star formation.

    6. Re:Does this qualify as a big bang? by lavagolemking · · Score: 2, Informative

      Except x-rays and gamma rays are light, being on the electromagnetic spectrum, and traveling at 299,792,458 m/s. Sound only travels around 340 m/s, depending on its medium. Also, if they were sound they wouldn't travel through space either.

    7. Re:Does this qualify as a big bang? by Yvan256 · · Score: 1

      I don't know if it makes any noise, but it does feel like having your brain smashed out by a slice of lemon wrapped 'round a large gold brick.

    8. Re:Does this qualify as a big bang? by Yvan256 · · Score: 4, Funny

      It's sound, Jim, but not as we know it.

    9. Re:Does this qualify as a big bang? by Charliemopps · · Score: 1

      All the air that exists, is in outerspace. So I'd say your argument is flawed.

    10. Re:Does this qualify as a big bang? by Black+Parrot · · Score: 5, Funny

      Whoosh... Thats the sound of a joke going over your head.

      If a joke goes over your head in outer space, does it make a woosh?

      --
      Sheesh, evil *and* a jerk. -- Jade
    11. Re:Does this qualify as a big bang? by Angst+Badger · · Score: 4, Interesting

      No. Sound is the vibration of air molecules, so when you speak or drop something, it creates compression waves that travel through the air and vibrate your eardrum, which in turn creates waves in the fluid of your cochlea that stimulate hair cells connected to the acoustic nerve. Since outer space has (almost) no air, these waves have no medium on which to travel, and sound as we know it does not happen.

      Well, yes and no. There's no sound in space that a human could hear -- especially over the deafening roar of their blood boiling in the near-vacuum of space -- but there is a tremendous amount of diffuse gas and dust in galaxies and galaxy clusters, through which compression waves travel, albeit very weakly and slowly. If you were to observe those waves, then you could convert that data into an audio waveform in the range of human hearing. I may be misremembering, but I seem to recall that a group of researchers did precisely that with the (vastly smaller, nearer, and more easily observable) waves of gas being propelled outward by the pulsar at the heart of the Crab Nebula.

      And yes, I know that really stretches the human notion of sound, but objects the size of galaxy clusters stretch most of our petty human notions, so it only seems fair.

      --
      Proud member of the Weirdo-American community.
    12. Re:Does this qualify as a big bang? by kwerle · · Score: 1

      Strictly speaking, sound does not need to be in air. Any gas, solid, or liquid will transmit sound (varyingly well).

      Huh. Will plasma transmit sound? I'm guessing not very well...

      IANAP

    13. Re:Does this qualify as a big bang? by dkleinsc · · Score: 4, Funny

      I'm not sure about a big bang, but it's definitely a cluster f*.

      --
      I am officially gone from /. Long live http://www.soylentnews.com/
    14. Re:Does this qualify as a big bang? by lavagolemking · · Score: 1

      See parent comment.

    15. Re:Does this qualify as a big bang? by MartinSchou · · Score: 1

      So ... if we were to vibrate your cochlea directly, without the manipulation of air (i.e. bone conduction), you're not hearing sounds, you're just having aural hallucinations?

    16. Re:Does this qualify as a big bang? by LurkerXXX · · Score: 1

      Larry Niven's outsiders and star seeds could probably hear the sounds of the collision.

    17. Re:Does this qualify as a big bang? by L4t3r4lu5 · · Score: 1

      You may be thinking of nebulae. They are clouds of dust and gas.

      However, on such a scale as this, who is to say this isn't similar to two clouds colliding? I would hazard a guess that on some microscopic level there is definitely a sound of water droplets colliding when two clouds merge. On a universal scale, I'd say two galaxies colliding would be quite close, proportionally, to that sound.

      --
      Finally had enough. Come see us over at https://soylentnews.org/
    18. Re:Does this qualify as a big bang? by nedlohs · · Score: 1

      No, we could see them if out eyes could pick up those, but we would never hear them.

    19. Re:Does this qualify as a big bang? by GooberToo · · Score: 1

      Technically, humans can hear some microwaves too because of the heating and cooling of your brain or inner ear. The US Air Force also has a patent on it. Supposedly, they can literally make you hear completely intelligible voices - according to the US Air Force.

    20. Re:Does this qualify as a big bang? by Urkki · · Score: 1

      Will plasma transmit sound? I'm guessing not very well...

      I'd guess the opposite, as interactions between ions in plasma are a lot easier (delivered through electromagnetic force caused by the electric charge) than interactions between atoms/molecules in neutral gas (delivered through collisions).

    21. Re:Does this qualify as a big bang? by rgviza · · Score: 1

      define noise.

      --
      Don't kid yourself. It's the size of the regexp AND how you use it that counts.
  2. Merger by Anonymous Coward · · Score: 5, Funny

    In a merger that size, the job losses must be astronomical.

  3. Near one of those simulated stars . . . by Mitchell314 · · Score: 1

    . . . does it have a planet with living beings running astronomical computer simulations?

    --
    I read TFA and all I got was this lousy cookie
    1. Re:Near one of those simulated stars . . . by toastar · · Score: 3, Funny

      . . . does it have a planet with living beings running astronomical computer simulations?

      not anymore

    2. Re:Near one of those simulated stars . . . by buchner.johannes · · Score: 4, Informative

      Actually, galaxy collisions are thought to leave solar systems undisturbed, with only a handful of collisions. The reason is that the space between the stars are so large compared to their size. Gas merges and spiral arms are distorted, but a planet would be fine. This is also what is expected of the Andromeda galaxy merge.

      --
      NB: The message above might reflect my opinion right now, but not necessarily tomorrow or next year.
    3. Re:Near one of those simulated stars . . . by chichilalescu · · Score: 1

      what does "handful" mean, in terms of percentage of solar systems?
      for instance, I understand that there are a lot of pluto sized objects orbiting our solar system. how close would a star (from another galaxy, which means it's moving in a completely different direction than the local surrounding stars) have to get to disturb those objects? I realize that in order to disturb a solar system, you need to disturb planet orbits (or destroy planets), but in order to seriously harm a civilization, considerably less disturbance is needed. For instance, a rogue moon sized object going through the asteroid belt might put a lot of them on different trajectories (that no longer correspond to the stable kepler orbits the planets are in).

      --
      new sig
    4. Re:Near one of those simulated stars . . . by Gotung · · Score: 1

      A solar system or planet might be "fine" in the astrological sense, but there is likely a much higher chance of objects in Oort clouds getting disturbed and sent hurtling towards your friendly neighborhood M class planet.

      In other words: one Bruce Willis isn't going to be enough.

  4. Obviously cool ... by ProfM · · Score: 1, Informative

    but simulating galaxy collisions have been done before: http://www.galaxydynamics.org/

    However, new to the simulation is dark-matter calculations.

    Cool none-the-less.

    1. Re:Obviously cool ... by Sean_Inconsequential · · Score: 1

      There is also GalCrash.

    2. Re: Obviously cool ... by Black+Parrot · · Score: 4, Informative

      but simulating galaxy collisions have been done before: http://www.galaxydynamics.org/

      However, new to the simulation is dark-matter calculations.

      Note that this is clusters, not galaxies.

      Also, DM *has* been modelled in galactic collisions before. I don't know about clusters, though.

      --
      Sheesh, evil *and* a jerk. -- Jade
    3. Re:Obviously cool ... by wvmarle · · Score: 4, Informative

      This is more than galaxies: this is about clusters of galaxies. Slightly bigger scale...

    4. Re: Obviously cool ... by Mt._Honkey · · Score: 1

      I used to do simulations of galaxy collisions, and dark matter is the easiest part to put into the simulation because it is assumed to be collisionless. It just goes wherever the gravitational potential points it (of course, calculating that gravitational potential can be somewhat complicated if you want to smooth over the rough spots caused by the finite number of particles simulated). The hard part is the gas, which has much more complicated physics due to the collisions, heating, cooling, and radiation on top of the gravitational physics. This also removes the scale-independence from dark-matter-only simulations. These are some of the reasons why early galaxy simulations were largely of elliptical galaxies, because they contain negligible amounts of gas.

      --

      Don't Bogart the fish sticks
    5. Re: Obviously cool ... by Limburgher · · Score: 1

      I don't think a galactic collision would realy influence Depeche Mode all that much. . .

      --

      You are not the customer.

    6. Re:Obviously cool ... by ImprovOmega · · Score: 1

      This is more than galaxies: this is about clusters of galaxies. Slightly bigger scale...

      But what's a few orders of magnitude between friends?

  5. no sound, but it makes a huge... by thejuggler · · Score: 2, Funny

    disturbance in The Force.

  6. Science by graphical bedazzlement by rbmyers · · Score: 2, Insightful

    The Department of Energy totally loves this kind of publicity. They want you looking at their pretty pictures and saying "Oh, wow!" The bureaucrat with whom I constantly spar over this science (and computer budgets) by pictures denies that the pictures are all that important, but we are constantly bombarded by them. The science and the numerics here may be great or they may be garbage. It doesn't matter all that much, I claim, because the people who vote on budgets and write the checks would never know the difference. Might as well turn it all over to Pixar for all anyone could prove one way or the other.

    1. Re:Science by graphical bedazzlement by Sarten-X · · Score: 5, Insightful

      Graphics give understanding, though. A numeric analysis can show exactly what happens, but it doesn't convey a general idea of what's going on. Pictures are easier to understand, and show more information at once. There's a reason why the weatherman shows his forecasts on a giant map.

      Speaking of giant maps, I visited the ANL recently, and saw a computer system being used for related research. If they're using the same visualization system (which looks REALLY similar to the video in TFA), then this graphical model could be shown on a giant screen, and the model could be rotated & zoomed at any point. It's science through pictures, not just pictures of science.

      --
      You do not have a moral or legal right to do absolutely anything you want.
    2. Re:Science by graphical bedazzlement by rbmyers · · Score: 1

      The DoE recently published a "prediction" that showed the oil from Deepwater Horizon racing up the east coast. As far as I'm concerned, the assumptions and methodology of the simulation were indefensible, but that didn't stop the Wall Street Journal from picking it up. While the DoE's *official* position was that the simulation wasn't necessarily credible as a "prediction," one of the NCAR scientists involved was quoted as saying that they realized that they had "the perfect model" for predicting the fate of the oil. The "prediction," of course, as compared to reality, was complete nonsense. As it stands, we still don't really know what happened to all that oil, but a picture in the Wall Street Journal left the impression that, not only did the DoE know exactly what was going to happen, but that what was going to happen was likely catastrophic. That's not science. That's not even defensible. Flow visualization has a long, important, and honorable history in fluid mechanics, but, in the past, you actually had to make some actual fluid flow to get a visualization. Now all you have to do is turn a computer on, and, if the results don't look completely crazy, people are led to believe that the science is credible. Maybe it is. Maybe it isn't.

    3. Re:Science by graphical bedazzlement by ceoyoyo · · Score: 1

      So what you're saying is that science grants should be decided by people who know something about science? That's a great idea.

    4. Re:Science by graphical bedazzlement by Sarten-X · · Score: 4, Informative

      That's because the Wall Street Journal, like so many others, confuses the meaning of the visualizations. They aren't results. Instead, they're great tools for finding what parts of the theory need a better test.

      As a contrived example, let's say that this visualization shows that a plume of dark matter going in a particular direction at a particular time. Comparing the visualization at that time to known colliding clusters in the real world might help show where to point our telescopes for evidence of dark matter. It helps to create the initial hypothesis, reducing the number (and therefore the cost) of failed experiments.

      Another use is for verification of a model. If we already know of several colliding clusters, this visualization should, be able to produce images that look very similar to those clusters. If not, then we know that there's something wrong with the model, and we can find ways to improve it.

      Tying that in with your example, we now know that the fluid model used wasn't perfect. It's time for more analysis, experiments, and refinements, eventually resulting in a more thorough knowledge of our universe.

      No scientist worth their salt will say that any model is absolutely perfect. In fact, the one you spoke of didn't. She said it was the "perfect model to do <a given job>," implying that it could do the job with the given parameters, and that deriving a completely new model wasn't necessary. The model itself is imperfect, but it fit the job perfectly. If the journalists presented the model as a prediction, that's the journalists' fault.

      --
      You do not have a moral or legal right to do absolutely anything you want.
    5. Re:Science by graphical bedazzlement by rbmyers · · Score: 1

      You're talking to someone who has done a fair bit of simulation and listened to others describe their own simulations. The simulation the Wall Street Journal bought into was wildly beyond naive. I told the author to ask an oceanographer, and he did. A later article, without simulation pictures, gave a much more accurate assessment of the unknowns. I'm not an oceanographer, but I've done ocean simulation, and I'm very familiar with the computational techniques employed. As a predictive tool for that situation, what NCAR and the DoE did was absurdly naive. People often have things wildly wrong and keep cranking out wrong results and briefing to them for years. I've seen it. I've been through it. Yes, simulations can be an aid to the imagination, sometimes a powerful aid, but the simulation itself is not science, and it's the confusion of pictures with science that bothers me. It's not a question of models being sometimes less than perfect. Sometimes, they are just WRONG. In the case of the Wall St Journal simulation, the results were complete misdirection. Not a useful clue to anything. The simulation assumes that dye injected into the mixed layer, and that is neutrally buoyant and passively follows the surface currents is a good proxy for the oil in the Gulf. None of that is remotely true for the Deepwater Horizon situation. The oil had complicated behavior that is different in so many ways from a passive dye tracer that it is hard to enumerate them. The "scientists" who cranked up the $100 Million code should have been smart enough to know that without even turning a computer on. As so often happens, though, they got a picture and could make up a good story to go with the picture, so the fact that it was a total waste of time and money is lost in the shuffle. I will concede one lesson learned: the DoE had no useful tools for predicting the fate of the oil in a catastrophic spill. For the problem presented for the Slashdot article at hand, there are not just the usual difficulties of fluid mechanics, but exotic physics that are, at this point, completely speculative. Those calculations are *expensive*, Asrophysics is awash in data. Maybe complicated, expensive simulations of unknowable accuracy are the only way to get a handle on the data, but it's pretty desperate science, and, with so much data out there, I wonder about the level of effort and credibility that is given to simulation. I certainly think that, "Oh, wow" is unjustified.

    6. Re:Science by graphical bedazzlement by rbmyers · · Score: 1

      Knowing something about science, unfortunately, is not enough. The problem with pretty pictures is that they are far too easy to make, and the level of detail offered by a typical fluid mechanical simulation implies something about the accuracy of the calculation that is often unsupportable in theory or in practice. What's the point of gorgeous pictures if the prediction is incorrect? We don't really know all that much about the detailed physics of hurricanes. Predictions of hurricane tracks are notoriously unreliable as have been "hurricane season" forecasts. Google "met office criticism" for a snapshot of the kind of criticism that the British office for predicting climate and weather has come under. The forecasters and the funders know *something* about science, but maybe not enough. My point here is that the engaging visual detail of fluid mechanical simulations has led to far too much uncritical acceptance of work that is often highly speculative and maybe, as a prediction, just flat out wrong.

    7. Re:Science by graphical bedazzlement by ceoyoyo · · Score: 1

      Acceptance by whom?

      The pretty pictures are for PR, or gross visualization. Are you arguing that scientists should try to make their work more unpalatable to the public?

    8. Re:Science by graphical bedazzlement by rbmyers · · Score: 1

      Scientists should be very careful about creating misimpressions of how well a problem is understood by misuse of color graphics. In the past, you would have gotten an "artist's conception." Now we get "simulations." The difference to which the actual physics are understood or accurately represented may not be all that great. When people discover, as some must have in the case of the Gulf oil spill, that what they're been fed is useless or worse, they rightfully become skeptical of the scientific enterprise. The fact that so much cutting-edge physics is still speculative is completely lost, and we wind up with misunderstandings of what science can and cannot do. It would come as a surprise to the general public, for example, that there is much about the simulation of fluid flows that is not understood. Computational "scientists" want their computers paid for and their work funded. What happens in the pursuit of that goal is often not only not science, but antithetical to science.

  7. Car Analogy by ijakings · · Score: 1

    Just some minor damage around the red shifting, thatll buff out.

  8. Hopelessly confused by dark matter. by Anonymous Coward · · Score: 3, Interesting

    I'm confused by "As the two clouds of dark matter inside each cluster can only interact gravitationally"

    If dark matter can interact gravitationally wouldn't this mysterious crap just accumulate in the gravity wells of massive objects like stars or even the earth the same way planets collect rocks and dust around them?

    Especially since everyone seems to be saying that dark matter so outnumbers normal stuff wouldn't a significant portion of the total mass that contributes to gravity of our own sun and earth be from dark matter?

    I don't doubt that dark matter contributes to gravity but to say that it has an effect in a way that would suggest it have "mass" is one of those moments where I go searching to find out what I don't understand this time because that makes no sense. If dark matter acted as "stuff" that had mass then surely it would clump!!

    Photons are massless but they have energy and therefore contribute to the gravity field even though they are not effected by gravity in the same way a massive object would be...the only effect is travling thru the pit created in the metric by the presence of "stuff".

    Please if there is anyone who can help me make sense of this I would be eternally grateful.

    1. Re:Hopelessly confused by dark matter. by Black+Parrot · · Score: 1

      If dark matter acted as "stuff" that had mass then surely it would clump!!

      I don't know about the scale of stars and planets, but it is strongly believed that DM "clumps" in and around galaxies. The effect on the rotation curves was one of the first things that tipped off the probable existence of such stuff.

      --
      Sheesh, evil *and* a jerk. -- Jade
    2. Re:Hopelessly confused by dark matter. by Anonymous Coward · · Score: 1, Insightful

      Bought that until you said "aether". Nice one! Almost got me to write an angry reply...

    3. Re:Hopelessly confused by dark matter. by wvmarle · · Score: 1

      I have similar ideas about dark matter. To me, DM is simply a way for scientists to explain their way out of issues we do not really understand. It's matter, but can not be detected. Doesn't interact with anything, apparently not even itself (in this simulation those "DM cores" simply pass through one another!), other than that it works on gravity. It's like aether - we don't know how it works, so we make something up to make it work. That's how it feels to me.

      There are problems with modeling galaxies: the calculations simply do not match up with the observations. So then the calculations are amended until they match up with the observations, and in this case DM is introduced. What it is no-one knows, I have not even seen any reasonable explanations of what it could be, but it nicely makes calculations work out (especially as we don't know how much DM there really is so that remains a variable to play around with).

      What is clear to me is that on astronomical scales, our gravitational models break down. We will have to come up with a new model - until then maybe continue to work with DM, for lack of a better solution. There is simply a lot we don't know about in this world, that's for sure.

      Or think about the issue of the age of the universe. The current consensus is 13 bln years or so, but then you still hear about stars being of a similar age (the problem there is that they formed when the universe was considered still too hot for stars to form), or objects with possibly higher age, so that again is not something we can be really sure of. When this DM thing is settled we probably will also have to redo the universe age calculations.

    4. Re:Hopelessly confused by dark matter. by ceoyoyo · · Score: 1

      "If dark matter can interact gravitationally wouldn't this mysterious crap just accumulate in the gravity wells of massive objects like stars or even the earth the same way planets collect rocks and dust around them?"

      Other way around. Normal matter (the minority) tends to clump in areas where there's lots of dark matter. Dark matter itself clumps, as you predict it would, but not to the extent that normal matter does. Normal matter clumps partly due to gravity, but to make nice tight clumps like stars you need friction to slow everything down and make it stick together. Dark matter wouldn't do that.

    5. Re:Hopelessly confused by dark matter. by TapeCutter · · Score: 1

      "What it is no-one knows"

      The same is true for gravity, science does not know what it is just describes how it behaves. Essentially ALL the fundemental forces and dimentions in the universe are "miricales" that have no explaination.

      BTW the oldest star is thought to be 13.2byo, the universe is 13.7byo, meaning the first stars formed some 0.5 billion years after the big bang.

      --
      And did you exchange a walk on part in the war for a lead role in a cage? - Pink Floyd.
  9. Flash Center by The+Yuckinator · · Score: 1

    the Flash Center at the University of Chicago

    They used Flash to simulate a galactic collision?

    And you thought it wasn't good for anything...

    1. Re:Flash Center by sensationull · · Score: 3, Funny

      Flash, What better platform is there for simulating something that takes billions of years.

  10. Big Deal by aashenfe · · Score: 1

    I have a screensaver that does this already.

  11. oh yes, dark energy by goffster · · Score: 1, Informative

    Let's bundle up all of the errors in our model of the universe
    and call it "dark energy". I say... "it is dark as ignorance".

    1. Re:oh yes, dark energy by Kagura · · Score: 2, Insightful

      It's better than fudging a cosmological constant into all of our equations.

      Unless you still believe in the steady state theory.

  12. The Flash Center? by Anonymous Coward · · Score: 1, Funny

    Oh man, Apple's going to be pissed!

    1. Re:The Flash Center? by froggymana · · Score: 1

      It should really be the HTML5 center.

      --
      "To prevent this day from getting any worse, I'll just read ERROR as GOOD THING" 1GJU8xLuDKDxEs4KLf8fAGyptoDsqvEsBT
  13. Reached the same result with 200 lines of Python by ttsiod · · Score: 1

    My naive Python simulator of gravity (200 lines) reached the same conclusion - expansion occurs. See the video and get the code from here: http://users.softlab.ntua.gr/~ttsiod/gravity.html

  14. For a highly technical idea... by Notquitecajun · · Score: 1

    Imagine a Beowulf Cluster of these!

  15. I've seen these in the 1990s by peter303 · · Score: 1

    So they can make them 10,000 times larger now. Whats the point of this post?

  16. Re:Awesome use of computer power... by suso · · Score: 1

    Also:

    • Climate change starting to affect things
    • No real defense against something like an asteroid hitting the earth.
    • Communications still affected by solar flares
    • Also, could you make the battery in my cell phone last longer.

    But that's ok, we know what will happen when two galaxies collide.

  17. I have the utmost faith in this model... by rgviza · · Score: 1

    ... considering we can't even model our own climate with any semblance of accuracy.

    --
    Don't kid yourself. It's the size of the regexp AND how you use it that counts.