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Space Science

Milky Way & Andromeda Collision 128

Posted by Hemos from the pretty-pictures dept.
Frédéric writes: "A lof of people know that our Sun will be a red giant in about 15 billion years, and its size will increase dramaticaly beyond the Mercury orbit and we will burn. But do you know that the Andromeda Galaxy will collide with our Milky Way in about 3 billion years, a first time, then another time after 1 billion years to merge themselves, what a mess! There is some pretty nice simulations in MPEG, and a lot of pictures with some explanation. The simulator use 24 million particles, they are planning a 120 million particles simulation."
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Milky Way & Andromeda Collision More

Milky Way & Andromeda Collision

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  • Re:I think they are trying to nudge us (Score:1)

    by Anonymous Coward
    How is this a Troll?

  • Re:Jesus, where did the time go?* (Score:1)

    by Anonymous Coward
    AFAIK the total lifetime of our sun is about 8 billion years, with 4 billion years old that makes it up to 4 more billion years left for us.
    The whole universe is about 12-18 billion years old. Our sun is a second generation star, build mostly of matter left from other, first generation stars. (this is the reason why there is matter with higher atom mass than iron on earth, it's the remains of supernovas.)

  • Re:n-body problem resources. (Score:1)

    by Anonymous Coward
    John Dubinski uses a parallel tree code. basically a Barnes-Hut tree with the 'local essential tree' method for parallelising. The ~O(N) FMM is a nice idea and works well in 2D, but in 3D it's a major memory hog and O(NlogN) trees are better.

    http://xxx.lanl.gov/abs/astro-ph/9603097
    his new code (which I'm working on too) is better :-)

  • Java Galaxy Collision Sims (Score:1)

    by Anonymous Coward

    You can simulate colliding galaxies on your home computer using the Galcrash [cwru.edu] java applet. There are also several other nice astronomy java applets on this website. It's a cool way to spend the afternoon.

    Yay astronomy!

  • It's a matter of scale... (Score:1)

    by Anonymous Coward
    In the big picture, on average, the universe is expanding. Compared to the overall scale of the universe, however, our local group of galaxies is a very small thing, so local motion within the group is the effect we see.
  • You assume uniform density of stars. So the chance of star collision on the periphery is much smaller than the probability you gave, but the chance is much higher if center collides with periphery, or even higher if center collides with center. What's the chance of star collision if center collides with center?
  • First off you're right on about radio waves. My guess is that there's some way to communicate (if not actually travel) FTL.

    And yeah, I also doubt the idea of massive colonization. It seems likely that most civilizations able to progress to the point of having that technology would first have to stabilize their population. Without exponentially expanding population, there's no need to colonize millions of worlds(and anyway, who wants to go live on planets where the air is toxic to you - which I bet for any given life form most planets would be).
  • The xlock -mode galaxy code is far from being an accurate simulation, it just looks interesting.

    Long ago, I wrote up a more accurate n-body simulator called XStar [midwestcs.com], along with an introductory text on the n-body problem [midwestcs.com]. XStar isn't that accurate either, as it is only a 2D simulation, rather than a 3D simulation, and the dynamics of a million particle system is very different than a system with only a couple dozen stars. Still, it is pretty accurate for what it does and will give you some insight on how stuff really works.

    To give you some idea how old XStar is, it was designed on a 33MHz 486 on a 1024x768 display. If you run it, make sure you add more stars, as in "xstar -b 50" or even "xstar -b 200" if you have a fast computer.

    --

  • The stars don't collide as such, true, but the orbits of the stars around the galaxies obviously change significantly. More importantly, the gravitational shockwaves (visibile as spiral arms etc.) cause regions of the interstellar medium to collapse and begin star formation.
    You could also imagine that as the orbits of stars are altered, so will the object orbiting them, so you might find that, eg the planets of a solar system like ours would be showered by comets and meteors.
    It would be interesting to see if new "stable" multiple star systems would be formed. Would solar systems combine? If two stars came close, would they eject each others planets?

    Sounds like a very interesting field of research.
    :)

  • "There's one thing every scientist on the planet agrees on: whether it happens in a hundred years, or a thousand years, or a million years, eventually our sun will grow cold, and go out. When that happens, it won't just take us, it'll take Marilyn Monroe, and Lao-tsu, Einstein, Maruputo, Buddy Holly, Aristophanes - all of this. All of this was for nothing, unless we go to the stars."- J. Michael Strazynski

  • Self-preservation is a human instinct, as is family preservation. The preservation of the race is just an iteration of this instinct over the population. People that lack this sensibility are known as sociopaths. If the survival of the human race is not a concern then why bother with anything? Just start walking down the street like Neo and get things going. See also sociopath.
  • > Oops - my bad; it's just LA that're taxing stuff that isn't even on their planet.

    If you have any evidence that Andromedans have a corporate base in LA, I think we should be told.

    --
  • How can you be sure that the earth orbit wouldn't be disturbed by ripping up Mars?
  • I think we're in big trouble if another star gets even close to our solar system. Which is a lot larger than just the sun...

    We'll be jolted out of orbit.
  • when that system could be predicting next weeks Lotto numbers. Sign me up for an account.
  • We've got Bruce Willis on standby to go blow it up.

    --
  • Damn! There goes my nightime navigation.
    ----------------
    "All the things I really like to do are either immoral, illegal, or fattening."
  • I'll make sure to buy term life insurance.

  • Just blame the police; it was the gravitational force between their car and yours that made you go that fast when they were trying to pull you over.
  • Well, that's just typical! Where are we going to find a mint condition Bruce Willis in the year 1.002.001, eh?

    On a brighter note, I bet Natalie Portman really will be petrified by then, so odds are that we'll go out with a meaningful comment on Slashdot.

  • As Moon has no atmosphere, the satellites and spacecrafts could be build easily (no messing with cleanrooms, no out-gassing problems) over there from local raw materials.

    Spacecraft and satellites are built in cleanrooms not to protect against atmosphere, but to protect against dust and dirt contamination. Dust and dirt will be a part of every human settlement, by virtue of skin flakes and hair if not due to dust and regolith from the lunar surface. So we'll still be building things in cleanrooms for now.

  • It's not surprising that the chance is practically 1 that _one_ star or more will collide. What would be more interesting is the chance that our Sun will collide or not. (Dividing your answer by your 1e11 gives a rather small probability of this).

    Your calculation doesn't take into account the size or star density of Andromeda, it assumes stars' cross-sections won't overlap, and it seems to be assuming the galaxies are colliding face-to-face. Also, I read some time ago that the Galaxy's radius was 110,000 light years, so area = nearly 5x10^10 ly^2, ie. 4x10^30km by my calculation.

    The galaxy's star distribution needs to be considered too. The galactic centre is _huge_, and probably contains a supermassive black hole. Whichever other stars get in the way of that are gonna be {insert synonym for bad occurrences}.

    There's a photo I've seen of two other galaxies colliding (although I forget what they are or which constellation it was). Their edges met at about 90 degrees, and the was a large empty black strip along where they were colliding. Hopefully someone reading this will be able to give an URL or upload their slide :)

    And finally, large gas clouds are no worries to those of us who have had to live with a compulsive farter
  • the machine that did these animations, the Blue Horizon, is actually one of the top supercomputers (last i checked, 8th). basically a shit load of Power3 (may have since been upgraded to Power 4's). It currently lives at the San Diego Supercomputer Center. more info: http://www.sdsc.edu/Resources/bluehorizon.html
  • "The two model galaxies, which eventually merge into one, toss several million stars into the intergalactic void before joining together."

    Would be one hell of a ride!
  • Since NASA's Space Budget is so horribly underfunded. By the time we get the funding to develop technology to go to other galaxy's we wont need to bother!!! THey're Comming To US!!!!

    Also... When the sun Goes Red giant.. Are we sure Any of the planets orbiting the sun won't be a million asteroids from collidinnng with some other foreign body in some other galaxy. Or even better. We get sucked into a bigger entities gravity well!!! Whee!!!!!!! I hope we get to orbit a really cool planet like that Roman Planet from the original Star trek. yea!!

  • I really doubt we could destroy ALL life on this planet. We could destroy lots of it, and ourselves in the process, but not sterilize the planet! And mutating viri are not really a problem for nature! They are to us, but were not really a long term concern for nature!!
  • Excuse me? What was Fermi smoking?

    From SciAM >...If extraterrestrials are commonplace, he asked, where are they? Should their presence not be obvious? This question has become known as the Fermi Paradox.

    This problem really has two aspects: the failure of search for extraterrestrial intelligence (SETI) programs to detect radio transmissions from other civilizations, and the lack of evidence that extraterrestrials have ever visited Earth.

    Erm..using that logic, we shouldn't exist. Our radio waves are not yet detectable outside of a ~ 90 light year radius and we've never visited another planet outside of our own freakin' solar system...

    oops. We're just figments of our.. *poof*
    3C
  • "And the collisions are not totally random, but I'd hate to do the math on that"

    The worsed case would be if the sun passed through the center of the Andromeda galaxy, stars are much closer together there, there is a hell of a lot of ionising radiation there, and a nasty 1 billion solar mass black hole (Galaxy formulation theories suggest that about 1% of a galaxies mass in the central black hole.) Even if the Sun and Earth missed any of the objects in the Galatic core, the Earth might still be cooked and the stripped from the suns orbit.

  • Oh, my god! A supernova so close to L.A.! How do we save Hollywood? Think of the children! Let's blame Canada.

  • It will take that long to get the EU to approve the merger.

  • I suppose that means that I'll have to change my pension plan and speed up construction of my concrete bunker. Ho humm, busy busy busy
  • Sterilizing the planet has been demoted to one of our minor feats for quite a while.

    The theoretical particle experiments that are going on at Fermilab and CERN right now are potentially able to create a certain theoretical particle called an instanton, which is supposed to be able to destroy the UNIVERSE, by resetting it's ground state. Something akin to that book in which a more stable form of water that is solid at room temperature is discovered and then a sample is accidentally thrown in the ocean.

    Comedy ensues.

    Oh, and, uh... as far as "we're not really a long term concern for nature".... that's a rather unhealthy anthropomorphism. 'Nature' isn't an entity, despite what some crackpot Gaians may tell you. Those people just read Clarke's Beyond the Fall of Night one too many times. Humans are just as 'natural' as anything else in the universe. The fact that some people consider the word 'artificial' to be the opposite to the word 'natural' just shows how meaning can be distorted by years of misunderstanding. If you consider what humans create to not be 'natural' then you have to consider honey in the same way. It's manufactured by bees, and it wouldn't exist without them. And, if you dig deep enough, you will find that 99% of everything you see when you go outside fits this relationship template.

    --
    "Seeker, what do you think of galactic civilization?"
    "I think it would be a good idea."
  • It's easy to say it's not a destructive process when you watch the event from orders of magnitutes of light years away, using the Hubble. But just because it looks purty over there doesn't mean such an event happening to OUR galaxy wouldn't be quite existance-threatening.

    Yes, galaxies are mostly empty space. Even still, there would be an uncountable number of collisions.

    No, astral bodies don't need to SMACK INTO each other in order to cause major changes in gravitation, orbit, climate, etc.

    Migrating to other star systems is a moot point in light of this event. How will populating another system in THIS GALAXY do anything to ensure our survival in an event that affects the entire galaxy?

    If we collide with Andromeda, I assure you that the entire structure of both galaxies will change forever, because we don't live in a Newtonian universe. The event won't simply undo itself.

    I think you need to read a little Gleick, Briggs, Peat, Lorenz, Hofstadter, Russel, Prigogine, Bohm, or Poincare. They all understand the nature of cause and effect a lot better than you seem to.

    Not that I'm trying to sow discord.
  • There are a number of promising methods of getting information (everything's information, right?) from one place to another faster than the fascist 186k mi/s speed limit. It seems to me they fit into two categories:
    taking advantage of common phenomena,
    and
    finding clever ways to bypass the problem.
    --
    The most immediately promising way to transmit information faster than light is by exploiting the nature of photons. One learns early on in quantum mechanics that photons are very weird creatures. They can become entangled. The exact nature of this relationship is beyond current human capacity to understand, I believe, but it makes for a very convenient situation. Almost a deus ex machina? Anyway, when photons become entangled, they become very self-conscious. They become obsessed with keeping up with the latest fashion trend. They become so obsessed that when their entangled pal changes her polarity, the other one changes to complement the polarity NOT at the speed of light, NOT "extremely fucking holy-shit fast", but INSTANTLY. And to make the situation further seem almost too convenient, entangled photons don't need to be materially near each other. After photons entangle, they can move to opposite sides of the universe and still INSTANTLY complement each other's polarity. Meaning if you change one, the other one changes. Meaning we as humans should be able to devise a system that takes advantage of this nature of photons. I have heard (I am sure most of you remember that /. article a while back on this) that "they" are experimenting with this phenomenon to "clone" photons, by using an odd double-entangled procedure. This same article said something to the effect that it violates sumsuch quantum law to pass MEANINGFUL information in this way. I myself don't see how that's possible. I don't understand why a machine cannot be devised that passively measures some effect of the photon's polarity change. This wouldn't violate the integrity of the photon's polarity, because it's only being PASSIVELY measured. Then why can't they use THAT setup to pass digital information across light years instantaneously? I guess I need to look into that.

    The second method is a little less polite. Speed of light? We don't need no stinking speed of light. The light barrier only applies to space-time. So even a child can postulate that if this odd "space-time" thing is giving us so many problems, why don't we just NOT USE IT as the medium? And I would pat that child on the head, smile, and say, "YOU JUST GOT AN ANSWER FOR EVERYTHING, DON'T YOU, YOU LITTLE LOUDMOUTH SHITHEAD?!" But I digress. That's the basis behind the Einstein-Rosen bridge (you know it from Contact, Event Horizon, and probably lots of other movies that don't cross my mind now). Basically it goes that since our space and time are pissing us off with these heinous limitations, we can just create our own alternative kind of space that connects two definite points in space and time. This alternative kind of space and time is not stable enough to use as a parallel universe, and though there are doubts that physical matter could pass through it and still remain intact, we're MARGINALLY sure that electromagnetic radiation could pass through it with an acceptable loss. So I guess that means that wormholes are lossy transportation protocol :) There is a theory floating around (probably has been for some time) that certain naked singularities (black hole without an event horizon, because the singularity spins so fast) that are toroidal in nature instead of spheroidal could mark access points to ERB's because the donut hole would be subject to a whole lot of weird forces. I can't intelligently comment on that, because I don't know how something like that would work. But maybe someone else can elaborate.

    --
    As always, come and point out my stupid mistakes.
  • Dammit, and I was planning on becoming immortal and living for eternity. Maybe now I can put my energys into something slightly more feasible, like a decent open-srouce windows manager.....

  • I remember as a kid learning that the Sun was going to go red giant in 5 billion years or so. My first thought was "But we are swarn to protect the national parks!"
    Now in addition to moving the planit far enough away from the sun to protect the parks we now have to move the Milky way on top of that. O bother.
  • Yes. But, the practical way to "solve" n-body problems is... (wait for it)

    Numerically.

    Funny thing they used a supercomputer, no?

    :-)

    (What's that? You wanted an analytic solution????)

  • This feels just like that real-time trip to Alpha Centauri computer game. Can't we do a fast-forward on reality?
  • Do that enough times and you'll have Shakespeare for wall paper.

  • I was just about to post a reply asking you to explain what you meant, but I was suddenly enlightened.

    You're right: Stuff is cool.

  • ...And people complain that Slashdot never has anything cheerful to say...

  • all objects closer to another but because of their speed, I doubt many will actually collide

    I'll cite that when I get pulled over by the police for speeding again.

  • The distribution of galaxies throughout the universe is not uniform. This clumpiness results in regions where local gravitational interactions dominate local kinematics.

    In general, though, we see other galaxies as red-shifted (receding). Things tend to get more interesting at smaller scales (for Chinese values of interesting).

  • Your sig should be attributed to A.C. Clarke, not Issac Isamov. (Due to the nature of sigs on slashdot, if you fix this my comment will look weird because the fix will appear retroactively in your post, but hey, I can live with that.
  • How does a galactic collision affect planets in a galaxy?

    Consider a single star, not in a galaxy, with a planetary system like the sun. Nice and stable. But if it should be heading for a galaxy, what are the chances of it passing through without gravitational forces disrupting the planets?

    Interstellar separation may be large compared to stellar radii, but if you pass through enough stars there's an increased chance that you come near enough to one to affect the planets. Maybe.

    Baz
  • This event will completely overshadow the release of kernel 388472466124525.27324.212

    I am sure everyone will forget to update their kernel when the galaxies collide.

    On a less humorous note, has anyone read that a scientist claims that the Earth can be gradually moved away from the Sun, using the gravitational force of a comet? The side effect will be that we may lose the Moon in the process...



  • The side effect will be that we may lose the Moon in the process

    That would be nothing short of a disaster. I remember seeing a documentary on TV a couple of years ago where they showed that it was the gravitational pull of the moon in its particular orbit, that holds earth's axis in place. Thus stopping the spin of the earth from upending the poles or placing them somewhere completely different. We'd suffer terrible climate instability if the moon didn't exist where it does, and it's possible that life might never have developed here at all.

    Macka
  • I'm pretty sure it's estimated the sun will burn out and become a red giant in about 4 billion years.

  • That was Space: 1999. It's fiction, honest! :-)


    Chelloveck
  • All you people working on infinite lifespan projects might as well hang it up now. Just 3bil years is hardly worth it now is it?

  • Some scientists are speculating on 'Nemesis', a dwarf star on a very wide orbit (period 30 million years) around the Sun. They claim Nemesis is responsible for the mass extinctions, dropping comets to inner Solar System as it passed through the Oort cloud.
    It was not "some scientists" speculating. Nemesis is a wonderful book by Isaac Asimov. The theory is his, and although scientifically possible, is thought [by most] to be highly improbable.

    ---
  • Of course, in 3 billion years, this might not much matter, but for two colliding galaxies, its quite possible for both of them to pass through each other without any stars colliding. However, its extremely likely that one or two stars will come within a light year of Earth. What will happen is a lot of the debris in the Oort cloud which usually remains in long period orbits way way out there can be flung into the inner solar system (the same effect happens every 60 million years or so when the solar system passes through one of the spiral arms.

    When this happens, there are suddenly a lot more big rocks roaming around the inner solar system, and the chances of Earth getting hit by one of them increases dramatically.

    Of course, I personally don't plan to lose any sleep over this. :)

    -Restil
  • Both galaxies have lot of void space. Only here and there an object can be found so there's not much chance for real collisions. Off course gravite will pull all objects closer to another but because of their speed, I doubt many will actually collide. Can anybody give an estimate of how many objects will actually collide and what this means for live on earth?

  • Wrong. (Score:2)

    by rjh ( 40933 )
    Nemesis is the pet theory of Professor Richard Mueller, who (as of last I checked) was a physics professor at Berkeley.

    Really nice guy, too. In '93 I wrote him a letter and asked him what the status of the Nemesis Hypothesis was, and he wrote a very nice and thorough reply in which he indicated that Hipparcos, a satellite which was supposed to resolve it once and for all, suffered an instrumentation failure. They were falling back to a manual sky-search and were hoping to have it done by 2000.

    Given that it's now 2001 and we haven't heard anything, I think we can conclude either
    • The search is taking far longer than expected
    • Fundamental problems in the search methods kept it from being a productive observation
    • The search was concluded and nothing was found, and Nemesis is pretty much a dead theory
    ... That being said, Richard Mueller is a very serious scientist. It angers me when I hear people call him a kook for the Nemesis Hypothesis (not that the original poster did).

    The Nemesis Hypothesis was classic scientific work. It was a blindingly creative look at a very difficult problem. It explained past observations and made predictions for future observations. The hypothesis was, is, testable (admittedly, not easily testable).

    Compare this to superstring theory, which has no observational support, no experimental support, no predictions for future observations. While I like superstring theory--it's a really cool thought exercise--it's not science.

    So why is it so many hail Brian Greene (superstring theory luminary) as the next Einstein, and in the next breath condemn Mueller as a kook?
  • It's just like how two cars can collide despite the expansion of the universe. Our two galaxies are not big enough or distant enough to be affected by the large-scale expansion of the universe. Other effects are much more significant at these small <cough> scales.
    --
  • Sun's gonna go Red Giant in 5 billion years, not 15.

    Picky picky picky.
  • I wonder if my collision insurance from State Farm covers galaxies. Which driver would be at fault?
  • "Any sufficiently advanced technology is indistinguishable from magic." -- Isaac Asimov

    Arthur C. Clarke

  • why, if our universe is expanding, we have two galaxies that are going to collide?

    Because typical distances between objects in the universe (such as superclusters [google.com]) are a lot Lot LOT bigger than the measly 2,300,000 light years [nasa.gov] between Milky Way and Andromeda.

    The expansion of the universe means things which are already very far apart will get farther apart -- "the rich get richer...". It has miniscule effect at the level of individual galaxies, where gravity is firmly in charge.

    You should now feel a whole lot smaller than you did a few minutes ago. On the bright side, you're still way bigger than quarks. :-)

  • If we don't begin to migrate to other planets and other star systems soon, we'll be doomed.

    Note that you're using the word "soon" in conjunction with an event 3 billion years from now. It seems to me that if we can get a self-sufficient Mars base within the next thousand years, and colonize [firaxis.com] other solar systems within the next million years, then we're way ahead of the game.

    Overpopulation, biological warfare, mutating viri.

    Overpopulation is generally self-correcting (starvation). It's also easily handled by public education and women's rights (see western europe). And as for biowar/mutation, I have justified belief in medical [google.com] progress [hopkins-biodefense.org] and the human immune system.

  • Will Mozilla be finished by then so people can watch the live webcast?
  • Oops - my bad; it's just LA that're taxing stuff that isn't even on their planet.
  • To spell out "numerically": in each iteration, you basically compute for each particle the total vector of gravity pulling at it and then move it a bit in that direction. Lather, rinse, repeat. Many, many times.
  • Never mind the fact that, unless we start to migrate to other star systems in the next few hundred years, there's little chance that any of our descendants will be around to see it.

    We're at a very delicate time in the history of our race. If we don't begin to migrate to other planets and other star systems soon, we'll be doomed. Overpopulation, biological warfare, mutating viri. All these things can lead to the destruction of all life on this planet.

    Anyone interested in this should really check out the book The Mote In Gods Eye [linkbaton.com] by Larry Niven and Jerry Pournelle. Mankinds first encounter with an alien species is with a species in much the situation described above. They can't efficiently get out of their solar system, which has led to all sorts of changes in their society, biology, traits, etc. Makes for an excellent read.

  • Colliding gas clouds would be very interesting.

    Just as water vapour moving very energetically in clouds produces lightning, I would imagine that colliding gas clouds would cause a lot of unimaginably intense electric charges.

    These clouds are also a plasma similar to the inside of a fluorescent tube, so the lightning would cause very intense bright flashes.

    Imagine the night sky being lit up by hundreds or thousands of bright flashes.

  • Dude, that's like saying, "Your going to spend all this time and effort building this huge Widget factory, when you can just carve Widget's out yourself?". Yes, of course there is a high up-front cost, but it's made up for in the long run. Economies of Scale, hello?
  • has some cookies... and it just wants to dip 'em in something!

    ----

  • It's fiction, honest!

    Actually, I think Macka is referring to, "What If We Had No Moon?" It was a Discovery Channel documentary narrated by (I think) Patrick Stewart. It discussed theories about how the moon formed, and what kind of effect its presence has had on life. Macka is right: one of the claims made on that show was that the moon somehow stablizes Earth's rotation, and its absence would allow the poles to point every which way.

    Interesting side note: the documentary also claimed that the moon is receding at 1.5 inches per year, so we'll lose it eventually anyway.

  • The hard radiation emitted by a nearby supernova will burn you and everything else on the side of the earth facing the nova crispy.

    True enuf, although I suppose the article cannot get everything right.

    Time to get out the 5000 rated sunblock

    ;-)

    Check out the Vinny the Vampire [eplugz.com] comic strip

  • There are two possible fates of the Sun which depend closely on the details of where it is in its galactic orbit at the time of the collision. In the first case the Sun may take a ride on a tidal tail and be ejected into the darkness of intergalactic space. In this case, our star would be all alone with few stellar neighbours so the night sky would be very dark with few stars to see -- maybe like the view of the nightsky from downtown Toronto. In the second case, the Sun is thrown right into the centre of the merging pair where a great starburst will be underway. The huge number of stars forming will result in supernovae going off at a rate of a few per year in the new merged galaxy. While these will not present a direct hazard to the Earth, they will truly light up the sky letting you read at night but probably frustrating the endeavours of backyard astronomers!

    I'm going to have to start taking bets on the outcome

    Check out the Vinny the Vampire [eplugz.com] comic strip

  • Why are they using the Startrek font on that "Quicktime" mpeg? Are they trying to get some funding for an escape plan?

  • Good thing that galactic spirals aren't due to winding, then, isn't it?

    An excellent online reference on density waves (the phenomenon currently thought to be responsible for the appearance of spiral galaxies) is at http://fuse.pha.jhu.edu/~danforth/spiral [jhu.edu]

    Density waves were proposed in the mid-60s and have (so far) stood up pretty well. What this has to do with the big bang or evolution is beyond me.

  • I thought that was about 8 billion years? Anyone?

    5 Gy is the rule of thumb figure. I even just asked a passing solar physicist about it... :-)

  • Could someone explain why, if our universe is expanding, we have two galaxies that are going to collide?

    As a layman, I would have thought that all galaxies would be moving generally away from one another.

  • Maybe it's just me but the complete annihilation of our solar system just has that effect on me =).

    Then again perhaps I'll catch that ride on one of those Vogon ships .. which reminds me ... plenty of time to invest some cash in a towel company..
    --

  • >A lof of people know that our Sun will be a red

    >giant in about 15 billions years

    I thought that was about 8 billion years? Anyone?


    >know that the Andromeda Galaxy will collide
    >with our Milky Way in about 3 billions years,
    >a first time, then another time after 1
    >billions years to merge themselves,

    This is indeed highly cool and it's nice to see some astronomy on /. ... it's now comonly accepted that our galaxy has already borged many smaller less-fortunate ones in the local group; shreds of their corpses (I'm not making this up! have been located in our galaxy by looking for stars with anomalous motions, ie fossilised fragments of things we ate long ago.

    Thing that gets me is, given that the Sloan Digital Sky Survey just found a quasar at redshift 6.2 (ie about 10 billion years old)... this is getting pretty close to the Big Bang... this doesn't give much time for our galaxy (or any others) to actually form, before we're switched on, full of stars, and eating our neighbours.

    The more I write, the more this sounds like some sick geek in-joke... [*1 10 points if you spot the reference
    --
    "I'm not downloaded, I'm just loaded and down"

  • Every day the sun gets hotter and in a little under one billion years the earth will be too hot for life as we know it. My suggestion would be start snapping up that cheap Mars real estate right now. It's always best to get in on the ground floor for the best prices.

  • In another 3 billion years, according to moore's law, our processors are going to have enough transistors to attract nearby galaxies just by turning on. i bet that didnt go into the particle field.
  • I am trying to quit smoking
  • Someone call our galaxy's insurance agent, and be sure to get some
    photos of the accident. I'd sure hate to be stuck with the
    repair bill on this one.
  • The simulator use 24 millions particles, they are planning a 120 millions particles simulation.

    I assume that's at least marginally more accurate than the screen saver that comes with my Linux distribution, eh?

  • Seeing this woke my curiosity...

    How carefully and realisticly can they predict all this? It must be very close to a chaos-theory if you ask me, *EVERYTHING* affects *EVERYTHING* and here they are saying what's going to happen in 4 billion years - bold.
    Of course people can guess and make it a good guess at that but really, how much time and knowledge have been put into these simulations. How much do we know about the world/universe around us to accuratly predict "so and so will happen..."? Is everything just based on what we know every starsystem looks like and it's position or is there more stuff to back it up?

    And besides, who cares? I'm long gone when these 3.9999999999999999 billion years has passed ;)

  • Pretty sim of colliding galaxies (Score:3)

    by dazed-n-confused ( 140724 ) on Wednesday July 11, 2001 @05:45AM (#92692)
    See the rather tasty java applet by Leonardo Boselli, Galactic Collider 1.0 [geocities.com], which shows how spiral arms are created when galaxies pass close by each other. You could change the start positions to whack two galaxies together, if that's what you really want to do...

  • The first gentleman had it about right (Score:3)

    by kfg ( 145172 ) on Wednesday July 11, 2001 @08:20AM (#92693)
    The child's site you point to correctly points out that the sun will * burn out* in about 5 billion years, however, it will turn into a red giant about a billion years before that.

    As for the 15 billion figure that is the estimated age of the *entire frikkin' universe* so I guess the author should get credit for having been able to attach a cosmological number with a subject of cosmology, but it's kinda like saying that Lincoln was assasinated in 1066.

    KFG

  • Re:So what does this mean? (Score:3)

    by glyph42 ( 315631 ) on Wednesday July 11, 2001 @04:11AM (#92694) Homepage Journal

    the chance that none of the 1e11 stars in Andromeda will collide with one of "our" stars is approximately 1 - (1e11 x 8.3e-19) = 1 - 8.3e-8, very close to 1

    Don't you mean (1 - 8.3e-19) ^ 1e11? I mean, assuming each potential collision is an independant, random event. However, according to maple, this is still roughly 1. Huh. Imagine that.

    By the way, if anyone around here actually read articles, someone might note that one of the researchers said that in the case where the sun ends up in the thick of things, the risk to the Earth is minimal, though the night sky would be quite bright due to all the starbursts going on.

    But I think the coolest part is right before the collision, when an entire half of the night sky is filled with a great big spiral galaxy! Holy mind blow!

  • Some Important Things to Note (Score:3)

    by theDunedan ( 462687 ) on Wednesday July 11, 2001 @06:19AM (#92695)
    There are some key points made in the original article. (http://www.cita.utoronto.ca/~dubinski/tflops/)

    One statement there says "the gap is closing at 500000 km/hour". I am not a professional astronomer, but I understand that we can not currently determine the proper motion of objects farther away from us than a few tens of light years. So although we know that Andromeda and the Milky Way are hurtling toward each other at 500 thousand kilometers per hour, we do not know how fast they are moving with respect to each other in the sideways direction. It is highly likely that the proper motion component of the relative velocities is greater than zero. If there is a high enough proper velocity, this would mean that the two galaxies, being in orbit about a common point, would miss when they came to their closest point and just fly right by each other.

    The article touches on this with "the best explanation is that the Milky Way and Andromeda are in fact a bound pair of galaxies in orbit around one another." But they make no reference to the unknown proper motion.

    Also, it is possible that the galaxy we live in now may well be the result of a historic collision of two smaller galaxies. The evidence for this is that the Magellinic Clouds are now in orbit around the Milky Way and are irregular. Now, this is speculation on my part, but that's allowed, isn't it.

  • Big deal. It's happening already. (Score:4)

    by dschuetz ( 10924 ) <davidNO@SPAMdasnet.org> on Wednesday July 11, 2001 @03:39AM (#92696)
    A few years ago, astronomers announced that a dwarf galaxy in the direction of Saggitarius was colliding with the Milky Way. I'm not sure it's exactly within our galaxy's borders [I'd thought it was, but the only reference I could find after a minute of googling said otherwise], but it's orbiting (every billion years or so), and the galaxies have had an effect on each other. Check out this FAQ about the dwarf [nasa.gov] and the referred page [seds.org]. Key quote: "It [SagDEG] is apparently in process of being disrupted by tidal gravitational forces of its big massive neighbor in this encounter. "

  • Who needs MPEG? (Score:4)

    by Bowie J. Poag ( 16898 ) on Wednesday July 11, 2001 @12:05AM (#92697) Homepage


    xlock -inwindow -mode galaxy &

    :)

  • Milky Way and Andromeda merge? (Score:4)

    by Mike Schiraldi ( 18296 ) on Wednesday July 11, 2001 @05:30AM (#92698) Homepage Journal
    Not if the EU has anything to say about it.

    --

  • Not such a big deal (Score:4)

    by Pedrito ( 94783 ) on Wednesday July 11, 2001 @12:18AM (#92699)
    Galaxies collide all the time. It's not a real destructive process. Look at the distance between stars. A "collision" of galaxies is like the collision of dust particles in a wind. There are very few stars that actually come into contact with each other, it simply increases the mass of the galaxy as a whole. We add a lot more stars to the galaxy and that's pretty much it.

    Never mind the fact that, unless we start to migrate to other star systems in the next few hundred years, there's little chance that any of our descendants will be around to see it.

    We're at a very delicate time in the history of our race. If we don't begin to migrate to other planets and other star systems soon, we'll be doomed. Overpopulation, biological warfare, mutating viri. All these things can lead to the destruction of all life on this planet. Then there are the less likely scenarios: Asteroid collisions, comet collisions. These too will happen, it's just a matter of when.

    But the actual collision of the galaxies, as I see it, is just another opportunity for us to have more planets to colonize.

    It also raises the possibility of us finding other life out there.

    Scientific American ran a great article here [sciam.com] about how the chances are, we're the most advanced species in our galaxy and why. It makes a great deal of sense. A collision with Andromeda could change that, and that I find interesting. Especially given the time frame. If we're to migrate through the galaxy, we could be in very good shape if Andromeda itself is already populated.

    But I'm just wandering off into all kinds of stuff completely unrelated. Sorry... I love this stuff, though.

  • Re:15 billion years? (Score:4)

    by gerddie ( 173963 ) on Wednesday July 11, 2001 @12:04AM (#92700)
    To be more accurate, it's about 5 billion years: Read it here [broaddaylight.com] and have fun!

  • n-body problem resources. (Score:4)

    by guybarr ( 447727 ) on Wednesday July 11, 2001 @02:33AM (#92701)
    solving the ODE's is done numerically.

    the main problem is of calculating the force on every star at every iteration.

    the problem was thought to be quadratic , but a decade ago was shown to be linear (by a PhD student named greengard) using spherical harmonics expansions.

    a very nice layman's introduction is at:
    http://www.amara.com/papers/nbody.html

    there are other sources linked there as well.
    keywords:
    N-body problem
    Barnes-Hut algorithm
    Fast Multipole Method (FMM)

    BTW I wonder what method they used, my guess is that at 10^8 stars an adaptive FMM variant is fastest.

  • Galactic Collisions and Starburst Galaxies (Score:5)

    by RobertFisher ( 21116 ) on Wednesday July 11, 2001 @01:42AM (#92702) Journal
    Galactic collisions are actually relatively common in Nature; typical galactic separations [psu.edu] are of order hundreds to thousands of kiloparsecs (kpc), whereas a typical galaxy is of order a few kpc in radius. Moreover, galaxies form along a highly filamentary spiderwork of structure [utoronto.ca] in the early universe, and tend to flow inwards to more massive galaxies.

    This situation is to be contrasted with the fate of stars during a galactic collision. Stellar radii are about 10^8 times smaller than the typical interstellar separation, so the vast majority of stars will simply fly right by another. A few stars will probably encounter a direct encounter (particularly if the initial pass is close enough to raise subtantial tides on the stars, which would act to drain energy and angular momentum from the system), but the vast majority fly by unscathed.

    It is true, however, that gaseous clouds in the interstellar medium are much more extended that stars, and collision between clouds (particularly giant molecular clouds) will be quite spectacular. It is hypothesized that cloud collisions as well as gaseous flows (bringing tremendous influxes of mass to the galactic nuclar region) resulting from galactic collisions can account for the tremendous bursts of star formation seen in "starburst" galaxies such as NGC 1808 [nasa.gov].

    In any case, the future collision of the Milky Way with Andromeda will be quite fascinating for far future Milky Way astronomers (if any are still around). Or perhaps for astronomers in other galaxies, far, far away...

    Bob

  • Re:How far gone are they? (Score:5)

    by Dr_Cheeks ( 110261 ) on Wednesday July 11, 2001 @02:11AM (#92703) Homepage Journal
    I'm long gone when these 3.9999999999999999 billion years has passed ;)
    Well, ignoring the fact that they say it's 3 billion years, not 4;

    4,000,000,000 years - 3,999,999,999.9999999 years
    = 0.0000001 years = 0.0000365 days = 0.000876 hours = 0.05256 minutes = 3.1536 seconds until you'll be "long gone". Since it's now considerably more than 3 seconds since the parent post was made, I'd like to offer my deepest condolences to the family and friends of Faile. Perhaps Slashdot could put up a black colour-scheme every July 11th in rememberence of this noble member of the community, who used his dying breaths to post to /.

  • California (Score:5)

    by Dr_Cheeks ( 110261 ) on Wednesday July 11, 2001 @12:12AM (#92704) Homepage Journal
    3 billion years, eh? That ought to give California plenty of time to figure out how to tax Andromeda.

  • Don't Panic... (Score:5)

    by EvilGwyn ( 120620 ) on Wednesday July 11, 2001 @02:23AM (#92705) Homepage
    Look, there's no point in acting all surprised about it! The plans for the destruction of the Milky Way have been up at your local planning office in the Lesser Magellanic Clouds for the last one and a half Hubble Times so there's no point complaining now! I don't know, stupid bloody apathetic Galaxy, I've got no sympathy at all!

  • What a way to start a morning (Score:5)

    by vicviper ( 140480 ) on Wednesday July 11, 2001 @02:59AM (#92706)
    "A lof of people know that our Sun will be a red giant in about 15 billions years, and its size will increase dramaticaly beyond the Mercury orbit and we will burn. " Who needs demotivators?

  • Re:So what does this mean? (Score:5)

    by Kite ( 200111 ) on Wednesday July 11, 2001 @12:50AM (#92707)
    Let's do a quick calculation here: The radius of the sun (a nice average model star) is about 700,000 km, so its cross section is 1.5e12 km^2. Let's enlarge the effective cross section for a bit to include the effects of gravity (stars attract eachother, so there's more chance that they will collide) to a nice, round 1e13 km^2. There are approximately 1e11 stars in the galaxy, so the total cross section of stars is 1e24 km^2. The radius of the galaxy is about 20 kpc, the total area of the galaxy is 1300 kpc^2 = 1.2e42 km^2, so the total fraction of the area of the galaxy that contains stars is 8.3e-19. the chance that none of the 1e11 stars in Andromeda will collide with one of "our" stars is approximately 1 - (1e11 x 8.3e-19) = 1 - 8.3e-8, very close to 1. I'll take my chances.

    The main danger, if I recall correctly, comes from colliding gas clouds. These are much bigger than stars, and about as common, so the chances this will happen are far greater. Colliding gas clouds tend to form stars, as their densities suddenly increase due to the shock, and some of those stars will be super massive ones that go supernova in a few million years. A supernova right nextdoor (on an astronomical scale, at least) is not something you want to happen, believe me.

    - Kite

  • Re:Not such a big deal (Score:5)

    by Caid Raspa ( 304283 ) on Wednesday July 11, 2001 @01:39AM (#92708)
    I think the collision of the galaxies will mean that some nearby-passing stars (nearby meaning less than 1 light-year) might disturb the Oort cloud, resulting in an increase of comets migrating to inner Solar System.

    Some scientists are speculating on 'Nemesis', a dwarf star on a very wide orbit (period 30 million years) around the Sun. They claim Nemesis is responsible for the mass extinctions, dropping comets to inner Solar System as it passed through the Oort cloud.

    We're at a very delicate time in the history of our race. If we don't begin to migrate to other planets and other star systems soon, we'll be doomed.

    I agree that we should be going ASAP. However, it is not possible to colonize the stars before have lots of experience on colonization in the Solar System. There's also some propulsion research to be done.

    Mars is probably within our reach, but it is not politically feasible. Even a simple manned mission to Mars would need global cooperation of all the major space players (USA, EU/ESA, Japan, Canada, Russia, maybe even China) as no-one has the money and political will to do it alone. I think the cost of a Mars-flight would be somethink like 1 Trillion US dollars. That would mean the American share would be of the order 400 Billion dollars.

    I think a permanent lunar base would be feasible. (I have read some ILEWG publicationts for this, and recommend them for anyone interested in lunar exploration. A google search should get you started.) The cost is estimated to be of the order 200 Billion US dollars, so it is a little more than ISS or NMD. However, there is lots of small-scale developments that could be done with less money. ESA and NASA are doing some small-scale research already. The Moon base could could be financed as a US/EU cooperation. Maybe Canada and Japan could also join. Thus the US share would be of the order 100 Billion dollars. So, all we need is the political will that makes the decision: Forget the NMD, we settle the Moon instead. Sigh....

    I'm sure one day we will turn the Moon to a real spaceport. Launching something from the Moon to low Earth orbit requires less energy than launching it from Earth. As Moon has no atmosphere, the satellites and spacecrafts could be build easily (no messing with cleanrooms, no out-gassing problems) over there from local raw materials. There's plenty of solar energy available in the Moon, so raw material extraction is possible.

    The lack of atmospehere could also allow launching of satellites with coil/railgun like devices powered by solar electricity. This would mean no cumbersome rockets wasting chemical fuel. (HCNO elements are not easily available on the moon, so chemical fuel would be stupid)

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