How do galaxies get their shapes?

Galaxies come in many shapes and sizes, but until recently astronomers have been at a loss to explain why. ... The behavior of a galaxy's dark matter halo could affect its evolution and help determine whether it becomes a spiral or an elliptical, they added. read more

These are the most common type of galaxies and among the most young one as well. These are classified with their planer structure and orientation, along with arms along which the stars reside. Most of the spiral galaxies have a large centre of gravitation or black hole. read more

If that is so, then a spiral galaxy’s arms are visible primarily because they’re made of hot, young stars, and these very luminous stars should live for less than one rotation of the galaxy. Estimates generally range from about 220 million to about 250 million years for the MIlky Way galaxy’s rotation. read more

Our galaxy, the Milky Way, is typical: it has hundreds of billions of stars, enough gas and dust to make billions more stars, and at least ten times as much dark matter as all the stars and gas put together. And it’s all held together by gravity. read more