There is nothing more violent than a collision between two entire clusters of galaxies. One such impact is so extreme, it could tell us what the universe is made of
Better dark matter science. It’s kind of long.
http://www.bbc.com/earth/story/20151215-the-most-violent-events-since-the-big-bang-itself
I’ve read that even if another galaxy would collide with our galaxy right now, there wouldn’t be that much chaos because there is so much space between solar systems, exo-planets, black holes etc even within a single galaxy. Can someone agree with this? I think the chance is very high that at least one solar system gets completely destroyed (maybe even ours).
Here you go, a bit of an old simulation, but it still paints a good picture, some would say chaotic.
Yeah, but would all planets really collide (or whole star systems)? Even in this simulation it looks like they don’t.
How much chaos there is really depends on what you mean by “chaos”. Colliding galaxies get very messy, taking relatively well ordered systems (like spiral galaxies) and turn them into disordered blobs of stars.
If you’re focused on collisions between stars or planets, however, galaxy collisions and mergers are rather quiet events. Let’s look at our solar system. Our Sun has a cross-section of about 12 trillion (1.2 * 1013) km2. That may seem big, but the empty space surrounding the Sun (with a radius out to the next closest star) has a cross-section of about 2 * 1028 km2. That means the Sun covers 1 quadrillionth of the empty “target area” it is embedded in. If this target area were the size of a standard dart board, the Sun would be one-quarter the size of an electron.
So, if you were shooting electrons at the dart board at random, what do you suppose your chances are of hitting the very specific fraction of an electron that represents the Sun?
Wasn’t the galaxy collision of andromeda and milky way (hmmmm milky way… where’s a snickers when I crave one) one of the more popular things you could do in universe sandbox?
Also, leaning out of the window a lot shooting in the dark, but I think that collisions of stars/planets would be less common than what you’d expect when you hear collision of galaxies… That is unless you get too close to either gravitational center.
I know that it’s very unlikely that a collision occurs. But when having hundreds of hundreds of star systems in each galaxy, wouldn’t the chance be higher that at least a few collisions occur? (even with our earth?)
The average distance between stars in the Milky Way is about 4 light-years. For the sake of argument, let’s cut this in half (making the average star the size of 1 full electron in our dart board example). That increases our chances of hitting that electron with another full-sized electron then raise to 1 in 5 * 1023. That means, for any given star, you would have to fire almost a trillion trillion stars at it, or 2 - 10 trillion times the number of stars in the entire Milky Way galaxy before we would expect to see that star collide with another.
There’s probably a bit more chance of devastation than that. A star travelling through the solar system (but missing a direct hit on the sun) would also probably cause something horrible to happen to Earth. If we take the target area to be a radius of 4AU around the sun that gives a cross section of 1.12×1024m². I work that out to be about 2 billionths of the dartboard. That’s still a very small target, but against that there would be hundreds of billions of stars heading our way. Although thinking about it further there would a lot less along any given trajectory that could potentially go directly through the solar system.
I calculate the area of a 4AU circle to be 25 billionths of the dartboard. I’m getting 4.52 * 1018 km2 for the area of a circle with a radius of 4 AU, while a circle with a radius of 4 light-years has an area of 1.80 * 1028 km2.
Even with a 1-in-2-billion chance of collision, that requires in the neighbourhood of 1% of all of the stars in the “shooting” galaxy to make a pass at a star before the chance of “devastation” becomes worrisome. And that climbs to over 10% of those stars to pass by at chances of 1-in-25-billion.
Note also:
Excluding planetary engineering, by the time the two galaxies collide the surface of the Earth will have already become far too hot for liquid water to exist, ending all terrestrial life; that is currently estimated to occur in about 3.75 billion years due to gradually increasing luminosity of the Sun (it will have risen by 35–40% above the current luminosity).
I remember a pretty good (if sometimes needlessly bleak) SF book(*) series where it is a plot point. An alien group taking the long view decided that anarchic spontaneously evolving intelligences were not to be trusted with managing such a big event, so they are careful preventing them to, you know, take over the galaxy. And by “take over”, they mean starting colonizing left and right, because once they start, who knows where they end. We can’t have that with the collision in only a few galactic years!
The point was that while direct system collisions were unlikely (IIRC, it gave an average 6 collisions), it would still be a big disruption at their scale - a scale nearly incomprehensible for mankind, though.
(*) You’ll recognize it if you read it, but I won’t reveal which one. It is kind of a spoiler, and this one is better enjoyed going blind.
A few days ago, I’ve read a proposal of stellar engineering for that: make 6 small suns from the Sun, and have them orbit it in a circle.
So you have 7 small stars with about the same global output, but that will run for way, way longer.
Personally, I’d just move the Earth around another star passing by. If none is arriving, moving one closer should do the trick.
Okay. I get it that the occusion of colliding objects is low but what about gravity? I just want to make sure our earth survives the galaxy merge somehow (for gods sake). I could imagine that the slightest impact on our rotation around our sun would be fatal, wouldn’t it? Just imagine how many objects in our galaxy would be impacted by gravity of the other galaxy’s objects. Wouldn’t that cause complete chaos or is the distance too high to have any changes?
Oh, Earth will be a barren dry husk by that point. No galaxy merger required. The oceans will boil half a billion years or more before Andromeda does its thing to us.
Well… let’s talk about how to transform our beautiful blue planet into a XXXL space ship… 
If you want to be pedantic it already is an XXXL spaceship. We just don’t have much control over it’s maneuvers 
You may think your body and mind are your own. In fact, you are a fusion of many organisms - including, potentially, another person. Words by David Robson,
photography by Ariko Inaoka
Besides your genes from parents, you are a mosaic of viruses, bacteria – and potentially, other humans. They are, in other words, a chimera
This would explain all the slightly disturbing but highly amusing articles in my local newspaper. I still have no idea how all these pineapples ended up in my house though.