If the galaxies are just because of black hole as black hole force them to stay at their places then the gravity near black hole must be grater then far places either planets or moons, then how it varies from one planet to another as from earth to its moon and to mars it means that there is black hole among them if not then how it varies
Responses (1)
The science of black holes is still not decided, some scientists believe that within some galaxies (maybe most/all), there is a Massive or even Super-massive Black Hole.
The Milky Way galaxy that we are part of seems to show some strange movements of very large objects around Sagittarius A* (* means star), this seems to prove a Super-massive Black Hole is at the center of our galaxy. This object has a mass around 4 million times our sun (Sol), whether the galaxy rotates around this object because it is there, or alternatively it has formed in that place because it is at the center of the galaxy is an unanswered question.
Your question is why do things stay where they are and is there a Black Hole keeping them there?
The same process is at work, but Black Holes aren't floating around influencing the moon and planets of our solar system.
The gravity between the sun and the planets keeps us where we are (orbiting the sun), the gravity between the planets and the moons keep them where they are (orbiting the planets).
The Sun rotates around the center of our galaxy because it is the center of mass, it simply weighs so much our sun orbits around it, but this mass is not just made up of the Super-massive Black Hole, there is an enormous bulge at the center of our galaxy that contains many billions of stars and planets, dust and gas. This is what makes us go around the center.
The variance in gravity between the different planets and moons is simply down to the mass of the object, the more mass = more gravity. This gravitational pull is tied in also with the distance between the objects, the closer the object the more influence it has.