A galaxy is a group of stars, compact stars, gas clouds, planets, cosmic dust, dark materia and energy that are united by the gravity in a more or less defined structure.
There are diferent types of galaxies, we can divide them following the Hubble scale.
- Elliptical galaxy: They go from their ellipticity, ranging from E0 to nearly spherical E7. Their appearance is elliptical; they show a little structure and usually have relativity interstellar mater.
-Shell galaxy: It’s a type of elliptical galaxy where the stars are arranged in concentric shells.
- Spiral galaxy: This galaxies look like spiralling pinwheels. The most of these galaxies exist in a roughly spherical halo of dark matter. Spiral galaxies consist of a rotating disk of stars and a central bulge of older stars.
-Barred spiral galaxy: They have a linear bar-shaped band of stars. It extends out either side of the core, then it fusions with in to the spiral arm.
The bars are supposed to be temporary structures that exist as a result of a density wave that’s going outwards from the core. It can also happen because of a tidal interaction with another galaxy.
- Super-luminous spiral: They are large galaxies with mass of 340 billion solar masses. These galaxies generate a big amount of ultraviolet and mid-infrared light.
- Peculiar galaxies: Galaxies that developed because of tidal interactions with other galaxies.
-Ring galaxy: Their structure looks like a ring made of stars and interstellar surrounding a bare core.They get formed when a smaller galaxy goes through the core of a spiral galaxy.
- Lenticular galaxy: It’s a galaxy with an intermediate form that has proprieties from elliptical and also spiral galaxies.
- Irregular galaxies: They can’t be classified as spiral or elliptical.
-Irr-I galaxy: Have some structure but doesn’t align with the Hubble classification.
-Irr-II galaxy: Does not have any structure that aligns with the Hubble scale.
- Ultra diffuse galaxy: Their density is extremely low. It can be as big as the Milky Way but has a visible count of 1% of the Milky Way.
- Dwarfs: They are small galaxies that contain just a few billion stars.
