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When Galaxies Collide 55

Posted by michael from the a-fox-special dept.
neutron_p writes "An international team of scientists announced today, they observed a nearby head-on collision of two galaxy clusters. The clusters smashed together thousands of galaxies and trillions of stars. It is the most powerful events ever witnessed. Such collisions are second only to the Big Bang in total energy output. The event was captured with the European Space Agency's XMM-Newton observatory. Scientists are calling the event the perfect cosmic storm: galaxy clusters that collided like two high-pressure weather fronts and created hurricane-like conditions, tossing galaxies far from their paths and churning shock waves of 100-million-degree gas through intergalactic space."
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When Galaxies Collide More

When Galaxies Collide

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  • I guess if something like that hits us, we're pretty much screwed...

    Kind of a sobering thought. I don't see that we could do anything about it though.

    • Re:I guess.. (Score:5, Insightful)

      by bandy ( 99800 ) <andrew.beals+slashdot@gmail.com> on Friday September 24, 2004 @06:07PM (#10345180) Homepage Journal
      It's not as if we wouldn't see it coming. Of course, if we're still stuck on this rock...

      And don't forget the wipe-out-nearly-all-life gamma ray bursts! No advance warning on those puppies.
      • "All of a sudden, causality decided to give physical laws and time the finger, and decided to instantly clash two random galaxies!"

        Um. Yeah.

      • Re:I guess.. (Score:3, Insightful)

        by Cecil ( 37810 )
        And don't forget the wipe-out-nearly-all-life gamma ray bursts! No advance warning on those puppies.

        Although that's only because we don't know anything about them.

        If one started happening near enough for it to bother us, I suspect we'd notice *something* going on beforehand. Energy can't just appear suddenly and randomly, it has to come from some source. And gamma ray bursts are a LOT of energy. I'm way too lazy to actually look it up, but I think it's at least on the scale of like, if an antimatter st
        • You're right of course.

          But I think it would be on the order of "say, that's weird"...."oh shit." One would have to happen far enough from us to be not fatal but still well-observable, not to mention that we'd have to be looking at it.
        • Stars about to produce a gamma ray burst would actually be pretty easy to find. The problem is that the type of abnormally massive star that produces them isn't that unusual, and red giant stars, which are what a pre-gamma ray burst star would be, are downright common.

          So if, say Betelgeuse (of Ford Prefect fame) was 100 times as massive as it really is and decided to collapse into a black hole one fine day 427 years ago, the only way we'd know about it would be looking at it a few hours before the burst h
    • The FA says we're running into the Virgo Cluster - ETA "a few billion years". So there's still time to pack.
      • hopefully we can get a decent space program by then. And fend off any asteroid collisions...

        Aw, who am i kidding. I'm sure we'll still be preoccupied with bush's national guard service and kerry's vietnam medals by then...
    • Hmm, not quite. The Andromeda galaxy is on a collision course with ours. Estimates say that the collision will take place in about 3 billion years and create a merger of the two galaxies. A collision between galaxies isn't like a collision between planets. I would predict a merger before a catastrophic explosion.
    • we're still worrying what to do about asteroids heading our way. maybe well-placed nukes solve that problem, but think about the size of the nuke required to deflect a galaxy heading our way...

  • Wouldn't the Galaxies just pass through each other (Score:3, Interesting)

    by Mystic0 ( 807930 ) on Friday September 24, 2004 @06:15PM (#10345222)
    Since the celestial an planetary bodies are extremely far apart relative to their size, wouldn't the galaxies just pass through each other without colliding at all?

    • RTFA (Score:5, Interesting)

      by empaler ( 130732 ) on Friday September 24, 2004 @06:22PM (#10345259) Journal
      Or at least look at the 'artist's impression [esa.int]'.

      They may be small and far apart, but the rules of physics does not allow preclusion from stuff like gravity and whatnot.
      • Gravity is fairly weak. It's the "whatnot" that always gets ya.
        • My phys teacher used to gripe for hours on end about the whatnot. Oh, and the whatyoumightcallits. Now *those* were the really bad ones...

      • Regarding the animation...
        So where does all the momentum of the smaller galaxy go? It seems like the pair of them should be moving together in the same direction as the smaller galaxy after colliding if they are going to merge.
    • wouldn't the galaxies just pass through each other without colliding at all?
      Generally, yes. But gravity would still be in effect, and so the galaxies would certainly be twisted and torn up and the like.

      How would it affect the Earth? Well, as long as no stars come too close to us, we'd probably not really be affected at all. We might get thrown out of our galaxy or something, but as long as nothing smacks right into our planet or our sun, and nothing distorts our orbit signifigantly, I wouldn't expect any real problems other than the nighttime sky changing ...

      ... of course, this would all happen or not happen over 100 million years, so any changes would be very gradual, at least as long as no stars get within a light year or so from us.

      • Re:Wouldn't the Galaxies just pass through each ot (Score:1, Insightful)

        by Anonymous Coward
        What intests me is the how the merging would affect time in the regions that came across intense gravity fields. IANP, any info
        • There's not really any reason to expect any intense gravity fields, not more intense than you can find in a normal galaxy anyways.

          Well, a giant star has a large gravity field, and if two giant stars were to collide, it would be even larger, but that's really about it.

          If a large star got close enough to us to affect the local gravity field enough to affect time, we'd all be dead long before, so there's little reason to worry about that. It takes seriously strong gravity (by terrestial standards) to

    • As they refered to it:
      "the perfect cosmic storm: galaxy clusters that collided like two high-pressure weather fronts and created hurricane-like conditions"

      Compare the planetary bodies to the molecules and atoms in the air. Compared to their size, they are pretty far apart, and yet affect one another when huge clusters collide. That's how I understand it.
      • Compare the planetary bodies to the molecules and atoms in the air. Compared to their size, they are pretty far apart, and yet affect one another when huge clusters collide. That's how I understand it.

        But the molecules in air collide quite regularly, and just bounce off each other, to a first approximation. When far apart their influence on each other is minimal. The bodies in a galaxy on the other hand influence one another at a distance due to gravity, don't bounce around between one another, and two
        • This calculator gives some perspective to the comparison: http://hyperphysics.phy-astr.gsu.edu/hbase/kinetic /frecol.html#c1 [gsu.edu]

          Just for interest sake, if you scale the time dimension to the same ratio as the space dimension (stars are ~10^19 bigger than a molecule), a molucule would collide with another (at STP) every ~100 years instead of 2E-10s.
          • Just for interest sake, if you scale the time dimension to the same ratio as the space dimension (stars are ~10^19 bigger than a molecule), a molucule would collide with another (at STP) every ~100 years instead of 2E-10s.

            Which is of course a lot more frequent than the observed rate of stellar collisions. The two situations are qualitatively very different of course, given that one is largely governed by long-distance gravitational attraction and the other by short-range electric repulsion, and so the c

            • and so the comparison is really not a well advised one

              It gets worse. The stars are generally further apart (when expressed as the ratio of their diameters) than the molecules in a gas are at STP. And the stars in a general area are usually moving in the same general direction, unlike molecules which are all moving about randomly.

              Also, gravity will generally only make two stars collide under very specific conditions -- what will usually happen instead when two stars wander into the same area is tha

  • Big Bang dead? (Score:3, Insightful)

    by SpaceLifeForm ( 228190 ) on Friday September 24, 2004 @06:15PM (#10345227)
    It the universe is expanding due to the Big Bang, then why would galaxy clusters ever meet?
    • Comment removed based on user account deletion

    • No. This has been understood for decades. (Score:5, Interesting)

      by Bootsy Collins ( 549938 ) on Friday September 24, 2004 @06:32PM (#10345320)

      It the universe is expanding due to the Big Bang, then why would galaxy clusters ever meet?

      The short answer is: because the Universe on these scales is not perfectly homogeneous. If it were, they wouldn't merge.

      The longer answer:

      Remember that the expansion of the Universe is an expansion of background space -- an expansion of the space in which everything is embedded -- rather than stuff moving through space. The rate of change of the relative separation of two hunks of matter can then be thought of as having two components: one from the expansion of space (objects staying in the same location, but the distances between objects are increasing because space is expanding), and one from the movement of objects through space (objects changing their locations in space). In the case of the latter -- the so-called "peculiar velocity" of an object -- if matter were distributed perfectly smoothly throughout the Universe, there'd be no reason for anything to change locations in space. But it isn't; and so there are net gravitational forces on objects that cause them to move. Whether the attraction of two objects "wins" over the expansion tending to separate them depends upon the situation.

      For a simple way to picture this sort of thing, consider a big rubber sheet with two marbles on it. Give one a nudge towards the other (its peculiar velocity), and then start stretching the sheet (the expansion of the Universe). Will they collide? Depends on the peculiar velocity, rate of stretching (expansion), etc. But it's certainly not the case that they always won't.

    • Think two cars driving along the highway, in the same direction (neighbors expanding away from big bang). Except that the one on the right is drifting slightly left, and sideswipes the other. Eventually. And then the crash goes into slo-mo for the next few thousand million years.
    • The rate of increase of separation between two galaxies due to universal expansion depends upon the distance between them. The greater the distance, the greater the relative coordinate velocity. When the distance between galaxies is fairly "small", as when they are members of the same cluster, they can be gravitationally bound, where the gravitational force overwhelms the weaker "repulsive" expansion.

  • hm.... (Score:2, Funny)

    by schnits0r ( 633893 )
    I felt a great disturbance in the force. As if millions of voices suddenly cried out in terror, then was suddenly silenced.

  • I'm sorry (Score:4, Interesting)

    by b-baggins ( 610215 ) on Friday September 24, 2004 @08:11PM (#10345810) Journal
    I just can't get my sky is falling hysteria worked up over a galactic storm that takes 100 million years to occur. I hope these folks aren't planning on watching the whole thing from beginning to end.
  • Somewhere out there, an extraterrestrial equivalent of George Clooney and Marky Mark are trapped on a capsized starship.

  • Our turn is coming (Score:4, Informative)

    by dpilot ( 134227 ) on Friday September 24, 2004 @09:11PM (#10346003) Homepage Journal
    Last I heard we were due to collide with the Andromeda galaxy. It must be around the hundred million or billion year range, though.
    • The last I heard was that two galaxies were colliding with the Milky Way and we just weren't aware of it until astronomers looked at the data the right way.

      • Re:Our turn is coming (Score:2, Interesting)

        by dpilot ( 134227 )
        I thought that was the Milky Way shredding the Magellanic clouds, and that that was largely a 'gravitational' collision. I'm under the impression that we have an up-and-coming collision with the slightly-larger Andromeda galaxy, and that the Milky Way will get the shorter end of the stick on that one. Given that both galaxies are about the same size, I don't think either will feel too good, afterward.

        The science fiction author Alistair Reynolds has a series of books that is partly driven by the impending c

  • Not the first time... (Score:4, Informative)

    by miope ( 727503 ) on Friday September 24, 2004 @10:38PM (#10346366) Homepage

    Obviusly, is not the first time it happens. Not so obvius, is not the first time this has been studied, either [space.com].

    By the way, there's a slighty more detailed article in space.com [space.com]., some other useful links in the article, also.

    Excerpt from space.com:

    The smaller cluster most likely contained about 300 galaxies, while its larger neighbor about 1,000 galaxies, researchers said. But when the two clusters collided with one another, they formed a still unsettled super cluster about 1 million light-years across that should take another billion years to settle down completely, researchers said.
    • Of course, maybe this time this collision gives more useful information than the collision studied in 2001 (see parent article).

      Note: Apparently, the clusters involved in the collision studied in 2001 are not the same than the clusters involved in this collision (so, two different collisions :-) ).

      Well... it seems this post is a bit confusing to read :(

  • NASA "Merger Website" (Score:3, Informative)

    by Anonymous Coward on Saturday September 25, 2004 @12:41AM (#10346748)
    Contains further information, videos, pictures.

    http://www.gsfc.nasa.gov/topstory/2004/0831galax ym erger_media.html
  • It is the most powerful events ever witnessed. Such collisions are second only to the Big Bang in total energy output. The event was captured with the European Space Agency's XMM-Newton observatory. Scientists are calling the event the perfect cosmic storm

    There's issues with the implied past tense in this story - this 'event' is still continuing and will do so for many millions of years to come. The impression is that a whole pile of galaxies just had a massive fender-bender and now it's all over.

  • Time (Score:3, Funny)

    by Alsee ( 515537 ) on Saturday September 25, 2004 @04:00AM (#10347288) Homepage
    Crap! Two galaxy clusters collide and I missed it!
    Anyone know what time it happened?

    -

  • targeted advirtisement (Score:3, Funny)

    by tloh ( 451585 ) on Saturday September 25, 2004 @04:07AM (#10347310)
    Did anyone notice the "Mergers & Acquisitions" ads by google? Considering the funding woos of NASA, perhaps......
  • smashed together thousands of galaxies and trillions of stars.

    In such an event, trillions of stars aren't smashed together. Some of the galaxies might merge, but individual stars would pass one next to the other with no harm - the space between them is much, much bigger than their dimension.
    • With so many stars moving past each other, the odds are that at least a few would be locked in death spirals with inevitable conclusions. Please don't be a killjoy and ruin the image of the BEST demolition derby in the UNIVERSE.
  • This seems like an good excuse for the network beeing down yesterday :)
  • that galaxy got quiet pwned to say the least

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