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Milky Way & Andromeda Collision
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."
See the rather tasty java applet by Leonardo Boselli, Galactic Collider 1.0, 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 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
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!
Music speeds up when you yawn, but does not change pitch.
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.
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 and the referred page. Key quote: "It [SagDEG] is apparently in process of being disrupted by tidal gravitational forces of its big massive neighbor in this encounter. "
xlock -inwindow -mode galaxy &
:)
Bowie J. Poag
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Mod up a post Rob doesn't like and you'll never mod again
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 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.
To be more accurate, it's about 5 billion years: Read it here and have fun!
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.
Working for necessity's mother.
Galactic collisions are actually relatively common in Nature; typical galactic separations 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 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.
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
Science, like Nature, must also be tamed, with a view turned towards its preservation.
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
3 billion years, eh? That ought to give California plenty of time to figure out how to tax Andromeda.
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!
Phear my l33t homepage.
"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?
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
- Kite
`But gravity always wins.'
- Radiohead