Galaxies

Certain types of galaxies have certain rules. Cases of deviation from the rules are handled on a case by case basis

Elliptical Galaxies

Elliptical Galaxies have rotational symmetry. The brightest region is the center where blue stars are located. As you get further and further away the planets and stars are older. There are deviations possible such as varying flatness, small imperfections in brightness fade, and slightly unaligned axis.

Spiral Galaxies

Spiral Galaxies are like our Milky way. Typically there are 2 - 6 rotating arms and rotational symmetry is present. At the center of the galaxy there is a high concentration of stars and there is typically some body holding things together such as a black hole. The central area is often red. Some subtypes exist

Barred: At the center there are 1 or 2 "bars" extending out. Rotating arms extend from them.

SO Galaxies

SO Galaxies are a sub-classification of spiral galaxies where they behave as spiral galaxies would, but they do not have the rotating arms. They do not have a definite edge, but a faint region around them. Some can be round while others being stretched or barred as a spiral galaxy would typically be.

SBO Galaxies

You have the SB and the O

Sa Galaxies

Sa Galaxies typically contain a large radiant nucleus surrounded by smaller more tightly packed arms made of dust or stars. Some variations can occur such as the appearence of multiple bulges in the nucleus region

Sb Galaxies

Sb Galaxies are intermediate. They can contain medium nuclei and somewhat spread out arms. Their arms are rougher than that of Sa galaxies and they can vary between very bright and not so bright

Sc Galaxies

Sc Galaxies are the largest of the spiral type. They typically contain small nuclei with large irregular and bumpy arms. The arms contain stars, dust and often times large irregularly shaped gas clouds, stellar associations, and star clusters. Sc galaxies make up a few subtypes:

Whirlpool (small nucleus and sharply curving arms)

Poorly defined arms (gas and dust is present between them making it not always clear on where they begin). There are other types, but this basically sums them up. The other types are variations on how unclear the arms are.

Sd Galaxies

This subtype was created to represent really faint spiral galaxies. They would likely not have large nuclei or as many stars. Some astronomers do not recognize this as its own subtype

Keep in mind that barred can go with any of the other subtypes of spiral (although they wouldn't be as prominent with more chaotic instances of Sc and Sd). They would be SBa, SBb, SBc, and SBd.

Ok. On to the next distinct type

Irregular Galaxies

As I was saying, Sc and Irregular can be hard to tell apart at times. Irregular galaxies don't contain a distinct nucleus or arms and end up being a blur of colors. There are 2 subtypes: Irr1 and Irr2

Irr1 are more common. They contain a very small to no nucleus. They are the ones that are often confused with Sc or Sd

Irr2 Galaxies are rare (and they are to be moderated as such) and can result from various causes. The most common cause is galactic cannibalism (it isn't officially called that) where two galaxies will tear each other apart leaving beind a chaotic mixture of the two galaxies.

Cd Galaxies (once again, we reserve the right to say no to them)

Cd galaxies are similar to SO galaxies, but can contain abnormally large nuclei. They are formed from dense clusters of galaxies and can be significantly larger than SO galaxies extending out for millions of light years.

Below are what I'll call "Emission galaxies" since they emit stuff

Curators should keep the amount of them under control to some extent. We do not need a million and a half of these. These galaxies were more recently discovered and have the common trait of releasing high volumes of energy, xrays, gasses, etc.

Radio Galaxies

Radio Galaxies emit a lot of gasses often caused by supermassive object in the middle. Gasses get released in a linear manner from the center.

X-ray Galaxies

Similar to radio galaxies, but they tend to absorb radiation and release it in a linear manner. X-ray galaxies cannot be seen by a planet with a similar atmosphere to Earth unless a telescope was sent outside it

Quasars

Quasars are clusters of X-ray and/or radio galaxies. They can release unusually large amounts of energy for their usually small size. They are the size of a solar system, yet emit 100 times more radiation than entire galaxies. Their emissions are similar to radio galaxies, but are red shifted due to the dopler effect. These emissions are red shifted enough to where identifying it may be a challenge.

S Galaxies

S Galaxies are galaxies near radio galaxies, x-ray galaxies, or quasars. They are often unstable due to gravity and get torn apart due to tidal effects to form a larger galaxy.

No, nebulae are not galaxies

A nebula is formed from a dying star. It can contain clouds of gas and dust. It is held together by the dead star's gravity.