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When simulating an actual merger with the two galaxies; any estimates on the number of stars that might collide? 400+ billion stars per galaxy might make each
by didgetmaster 1y ago
When simulating an actual merger with the two galaxies; any estimates on the number of stars that might collide?
400+ billion stars per galaxy might make each one seem 'dense' but the distance between stars is enormous.
I have heard that it might be possible for one galaxy to pass through another without any stars colliding with each other. I don't have any idea if that is actually true.
- banana_giraffe 1y agohttps://web.archive.org/web/20140701085917/http://www.nasa.gov/mission_pages/hubble/science/milky-way-collide.html https://web.archive.org/web/20140701085917/http://www.nasa.g... : > Although the galaxies will plow into each other, stars inside each galaxy are so far apart that they will not collide with other stars during the encounter. However, the stars will be thrown into different orbits around the new galactic center. Simulations show that our solar system will probably be tossed much farther from the galactic core than it is today.
- raverbashing 1y agoVery low probability times massive number of stars: yes I think there will be a non-zero number of actual collisions
- bruce511 1y agoYou are confusing one big number with another big number, and treating them as the same. Yes there are a lot of stars. It's a big number. But there's a lot of space. That's a number that's in a whole different league. For example, the whole solar system is about 2 light-day diameter. But it's 4 light years from the nearest star in any direction. Empty space is thus many orders of magnitude more than solar systems, never mind suns. Sure there's a probability of a collision. But even multiplied by the number if stars, it's still really tiny.
- raverbashing 1y agoI would agree, except for some factors: Gravity tends to bring heavy objects together Andromeda and the Milky Way are not colliding "like two pancakes on top of each other" but at an angle to each other Also star surroundings are usually places where you can collide with a lot of stuff (asteroid belts, dust, etc) We're not shooting a goal on a 4 light-year wide goalpost (btw that's the density on our vicinity, but on other areas the density is higher) but passing multiple stars on an environment that can be perturbed and heavy things attract each other
- karn97 1y ago[dead]
- aurareturn 1y ago[flagged]
- consp 1y agoUnless it can quote the paper which says that, show it and that paper actually validates it with good math, I'll treat it as a hallucination.
- Projectiboga 1y agoThe collision part of the merger could be over a very long time frame. So those few dozen might be spaced over many million years.
- MangoToupe 1y agoThis entire conversation seems silly without a time frame. Over a long enough time with continually interacting orbits, of course mass will coalesce. I don't think "merge" means "one time interaction that fully disperses the mass", anyway. If they merge in 7 billion years, you think over the eg next 7 billion there won't be kinetic collisions? I'm skeptical.
- 1y ago
- superfish 1y agoWikipedia has a nice size analogy: https://en.wikipedia.org/wiki/Andromeda%E2%80%93Milky_Way_collision?wprov=sfti1#Stellar_collisions https://en.wikipedia.org/wiki/Andromeda%E2%80%93Milky_Way_co... > […] if the Sun were a ping-pong ball, […] the average distance between stars […] is analogous to one ping-pong ball every 3.2 km (2 mi). Intuitively this visualization actually makes it seem like stars are pretty close? Usually with galactic dimensions it’s hard for our mere monkey minds to grasp the scales but this is actually pretty easy to imagine.
- snickerbockers 1y agoThat's because you're significantly larger than the pingpong ball.
- nandomrumber 1y agoSol is about 1.39 million kilometres in diameter. A table tennis ball is 40mm in diameter. That makes the sun about 34,750,000,000 times bigger than a pingpong ball.
- fecal_henge 1y agoI find some of these numbers hard to believe sometimes. 40 mm seems really big for a table tennis ball.
- a_shoeboy 1y agoIt's 0.00019884 furlongs, if that helps.
- nandomrumber 1y agoOr 0.0008 OSP (Olympic Swimming Pools) Edit to add: length, not volume
- 1y ago
- penteract 1y agoIf we assume that the stars of one galaxy (A) are distributed uniformly at random within a circular area in the galactic plane, and the other galaxy (B) is moving perpendicular to the plane of A and passes entirely through the circle containing stars, and assume that stars in galaxy B are point-like, then: Expected Number of collisions = Number of stars in galaxy B * cross sectional area of star in A / average area of galactic circle per star in A. https://www.wolframalpha.com/input?i=%28number+of+stars+in+milky+way%29+*+%28diameter+of+sun+%5E+2%29+*+%28%28number+of+stars+in+milky+way%29+%2F+%28diameter+of+milky+way%29%5E2%29 https://www.wolframalpha.com/input?i=%28number+of+stars+in+m... says it comes to 0.5 - 1.0 (the uncertainty comes from number of stars in the milky way) My assumptions are bad enough that it could be off by a factor of 100 one way or the other (there should be a few factors of 4/pi, it looks like Andromeda is about twice the size of the Milky Way, the average star is smaller than the sun, no stars are point like, gravity probably does something, stars are much more densely packed towards the galactic center, I'm calculating the result one galaxy passing through another, not a merger in which they might partially intersect more than once).
- rwmj 1y agoBut they don't need the stars to physically collide for it to be a problem. A star coming anywhere near the orbit of Jupiter would pull planets away from the Sun, which would make dramatic changes to the Solar System.
- simondotau 1y agoCorrect me if I’m wrong, but isn’t the scale of our solar system minuscule compared to the distance between stars? Presumably if another star gets close enough to affect Jupiter, it’s going to affect everything to varying degrees.
- rwmj 1y agoYes you're correct! It's about a factor of 50,000 between the orbit of Jupiter and the distance to the nearest star. But the orbit of Jupiter is still a lot bigger than the size of the Sun. To give numbers: The radius of the Sun is 700km, the radius of the orbit of Jupiter is 7*10^8 km (approx, it varies a bit), and the distance to the nearest star is 4*10^13 km.
- kristianc 1y agoInfinitesimally small. Like throwing a grain of sand from either end of a football pitch and expecting them to hit each other small.
- teamonkey 1y agoAs others have mentioned, the space between stars is vast, but also it's actually very hard for stars to directly collide. The reason for this is because the dynamical systems of gravity, conservation of momentum etc. tend to pull approaching stars into orbits around each other or make them slingshot away after a close approach, rather than collide directly. Even though intuitively you feel gravitational attraction would make it so that they pull together, the mechanics tend to prevent that from happening. It's the same reason that, unintuitively, it takes a lot of energy to bring a rocket from a stable orbit down to Earth. That's not to say that direct collisions won't happen, the circumstances will surely be there for them to happen, with all those millions of stars, just less likely than you'd think. When two stars collide it's usually because two stars are in close orbit and something causes an orbital decay, such as one leaching matter from another, or another star passing close enough to disrupt it. This last point is probably more of a catastrophic risk here; even more so the possibility of a passing star slingshotting planets away into open space. Source: this was part of my undergrad thesis.
- exe34 1y agoI think direct collision depends just on the geometric cross-section, no? Gravity can't repulse, so if you're on a direct collision path, nothing will move you off it. The whole slingshot thing is that you get close, you change path, but just because you pass close doesn't mean gravity will make you collide. I might be missing something...
- teamonkey 1y agoIf you have two stars moving directly and perfectly towards each other, and there are no other influences, then yes, they will collide. In reality there will be always some sideways motion for each star relative to each other, especially in this kind of situation with a lot going on. The gravity of the bodies pull on each other as they approach, accelerating them towards each other, but their momentum is strong, and so gravity pulls them into an elliptical orbit (or hyperbola) and not into each other. There only needs to be a tiny relative sideways motion for this to happen. In other words, gravity will not cause two stars passing very close to each other to collide, as one might expect. The stars really would to be aimed perfectly at each other to collide, which would be extremely unlikely with both stars feeling the faint pull of many distant neighbours. I think I was being overly cautious when I suggested a direct collision was likely to happen. It's more accurate to say that an accidental confluence of the many complex gravitational forces and sheer number of stars could maybe allow collisions to happen somewhere in that system.