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It's important to realize that the concept of a "galaxy" is arbitrary. Specifcally, it's not like stars suddenly stop and that's where the edge is. It's gradual
by jmyeet 5y ago
It's important to realize that the concept of a "galaxy" is arbitrary. Specifcally, it's not like stars suddenly stop and that's where the edge is. It's gradual.
And while the intergalactic medium has very little matter (often quoted as ~1 atom per cubic meter) it's not evenly distributed and there are stars. In the Milky Way stars are on average ~5 LY apart. In the IGM it's likely this number is more like ~1000 but it's really ahrd to say for sure.
Do the math. 1 LY = ~9.5e15m. A cube 1000 LY on each side is ~8.6e56m^3. The Sun is ~1e30 kg. For simplicity let's say that's all hydrogen. Avogadro's Number tells you thats 6e23 atoms per gram or 6e57 atoms in a space of 8.6e56, which comes out pretty close to 1 atom per cubic meter while there still being stars.
So the gas halos of the Milky Way and Andromeda galaxies are arugably already "colliding". I'm not sure this is a useful description of a galactic collision. There are gas structures in the IGM. At what point do you consider something to have collided exactly?
- burnte 5y ago> It's important to realize that the concept of a "galaxy" is arbitrary. Specifcally, it's not like stars suddenly stop and that's where the edge is. It's gradual. Eh, the concept isn't that arbitrary, it's the borders that would be more arbitrary. It's like asking where does a river end and the ocean begin. No one would argue the Atlantic isn't an ocean and the Amazon isn't a river, but exactly where you draw that border requires some discrimination.
- blueprint 5y agoWhen it would have fallen into the other gravity or magnetic well instead?