How is the galaxy held together?

Answer 1

Gravity.

To be specific, not only the gravity of all the objects inside the galaxy, but what's in the center:

Evidence points to there being at the center of all galaxies a supermassive black hole.

Supermassive as in larger than the largest star yet compact as if the entire Earth was compressed into a ball smaller than a marble. Thinking of this, you may just begin to see how supermassive they are.

It's pretty mind boggling. However, I'd suggest you continue your research, as I'm not the most reliable source. =P

Answer 2

The galaxy is held together by gravitational forces which keep objects orbiting around a massive center. Sometimes this center is a collection of stars, other times it is a supermassive black hole.

See related link for more information.

Answer 3

Gravity

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That is a good question,

We really do not know yet.

Our mathematical models even have a hard time describing what holds a galaxy together in a cohesive structure.

Answer 4

galaxies stay together because of gravity. in your solar system all the plants rotate around the sun because it has the largest mass in the solar system and therefore the highest gravity. but in the centre of most galaxies, there is a black hole so every thing in the galaxie rotates around it

galaxies themselves to not rotate around anything as they are all expanding outwards from a initial point call a singularity