What really holds galaxies together - Gravity or Dark energy?

It's very rare but a star can be created outside a galaxy. I don't have any examples but they exist and it's rare.

Gravity is the force that holds the universe together, and allows for galaxies and solar systems to exist.

There are a ton of extremely powerful telescopes both here on Earth and in space that is capable of looking billions of light years far. And we can see a...

We do know that protons and electrons which make up matter were created in the big bank. We also know that large numbers of photons were created which have now...

Many galaxies are members of groups or clusters. Since groups and clusters contain so many galaxies relatively close together, it should not be surprising that galaxies sometimes collide with each...

Most galaxies have a supermassive black hole at their centres. Most galaxies have little material falling into the black hole. Young galaxies and galaxies which have collided with others have...

Stars tend to exist in a binary setup. That is, two stars orbiting about each other. Our star, , is an exception although there is discussion that maybe a long...

When things fall to the ground, they are picking up energy from the gravitational field. In the case of Earth the gravitational field is modest but still offers enough energy...

Galaxies early on in their lives are actively forming hot, new stars and appear more bluish. Older galaxies are forming fewer new stars and their constituent stars are older on...

Gravitational force is a central force that pulls things radially inward. However objects, in general, have non-zero tangential components which contribute to their Angular Momentum. Angular momentum is a conserved...