What do superclusters orbit? Or what pulls them along in space in a direction?


So planets orbit stars. Stars orbit the galaxy. The galaxy forms super clusters with other galaxies moving through space.

What do galaxies orbit and when they form super clusters, what do they orbit/what determines direction/speed/etc of their movement?

From my understanding Andromeda and the milky way will one day collide in a billion years. So we’re obviously pulling each other together. Whats then pulling us along?

In: Physics

Momentum and gravity.

Gravity gets pretty weak on inter-galactic scales, but the masses involved are also incredibly large, so superclusters pull on other superclusters, and so on. But that’s a relatively weak force…mostly it’s because the superclusters are moving (relative to each other) and there’s nothing to stop them.

Even when the Milky Way and Andromeda run into each other we mostly won’t notice…there’s so much empty space even in a “dense” region like a galaxy that almost nothing is actually going to directly collide. But there’s going to be a lot of weird gravitational effects as very large masses get very close to each other.

Galaxy super clusters don’t orbit anything. They are the largest gravitationally bound objects in the universe. They are actually being pushed away from each other by the expansion of space.

At those scales you have to talk about average movement. A galaxy orbits around a central area, and that center of gravity moves through space. So you can think of the whole galaxy as a collection of mass that, as a whole has a gravitational pull outside of the galaxy on average. As galaxies in the same local cluster are relatively close to each other, they have a gravitational impact on each other. They all orbit a common center of gravity essentially, but as they do, they may collide and reform. Galaxy rich areas are on average gravitationally pulling each other together, even though they’re not single objects, they’re compact enough (relatively) that their combined mass is great enough to impart some heavy effects on other objects, even unfathomably distant but still within their cluster.

The orbits of the galaxies within a supercluster is guided by the center of gravity of the galaxies in the cluster. Basically the mass of the galaxies hold the cluster together and they move around the gravitation center of the overall mass. In the solar system that point is inside the sun, but if the solar system had two stars of equal mass orbiting each other the center of gravity would be a point in space half way between the two stars. Same concept, just with a lot of galaxies instead of two stars.

The motion of superclusters follows the same concept, except its based on the center of gravity of all the other superclusters/galaxies/what have you.

Overall there isn’t anything really “pulling” on us. Newton’s Laws of Motion explain this. If an object is moving in a direction at a velocity, it will continue to do so forever unless acted on by a net force. And every action has an equal, but opposite reaction. Any object that is pulling us towards it is also being pulled towards us by us. One will have a larger amount of motion due to differences in mass. The same force is applied, but the smaller mass will be accelerated faster by the same force.

If you say step off of a platform and fall a little to the ground, the entire time you are falling to the earth, the earth is also falling towards you. The difference in mass means that you travel almost the complete distance of separation, but the earth also moves the tiniest little bit (I’m talking sub-atomic distances).