Types of Stars

There are many different types of stars. Stars are classified into different groups based on their color, size, mass, luminosity, and more. Some star types are confirmed to exist, but some aren't, or are hypothetical. The main star types include; O, B, A, F, G, K, M, L, T, Y.

## Classification

Stars can be classified by luminosity using certain letter/number codes, with 0 (hypergiant) being the most luminous, and VI (subdwarf) being the least luminous. Below is a list of all the luminosity classes;

* **0** - hypergiants or extremely luminous supergiants
* **Ia** - luminous supergiants
* **Iab** - medium/intermediate-size luminous supergiants
* **Ib** - less-luminous supergiants
* **II** - bright giants
* **III** - giants
* **IV** - subgiants
* **V** - main-sequence stars (dwarfs)
* **VI** - subdwarfs

## Main Spectral Types

#### O-Type

*Main Article: O-Type Star*

O-Type stars are very hot and luminous. These stars are the rarest stars known to humans. About 1 in 3,000,000 of the main-sequence stars in our solar neighborhood are O-Type stars.

#### B-Type

*Main Article: B-Type Star*

B-Type stars are luminous and blue. O and B-Type stars are very active, which means they will only live for a short amount of time. B-Type stars are the second rarest star known to humans.

#### A-Type

*Main Article: A-Type Star*

A-Type stars are the more common naked-eye stars. A-Type stars are bluish-white. About 1 in 160 of the main-sequence stars in our solar neighborhood are A-Type stars.

#### F-Type

*Main Article: F-Type Star*

F-Type stars are white stars that are much more common than A-Type stars. About 1 in 33 of the main-sequence stars in our solar neighborhood are F-Type stars.

#### G-Type

*Main Article: G-Type Star*

G-Type stars are by far the most well-known star type, as our own Sun is a G-Type star. G-Type stars are yellowish in color. About every 1 in 13 of the main-sequence stars in our solar neighborhood are G-Type stars. G-Type stars can become supergiants (yellow supergiant), but are very unstable.

#### K-Type

*Main Article: K-Type Star*

K-Type stars are orange stars that are somewhat cooler than our sun. K-Type stars make up about 12% of the main-sequence stars in our solar neighborhood. K-Type stars can also be giants, supergiants, and even hypergiants.

#### M-Type

*Main Article: M-Type Star*

M-Type stars are by far the most common stars that we know of. About 76% of the main-sequence stars in our solar neighborhood are M-Type stars (red dwarfs). M-Type stars are very dim, so dim in fact that you cant see any with the naked eye. M-Type stars can become massive supergiant/hypergiant stars. Most of the largest stars in the Milky Way are M-Type stars, including Antares and Betelgeuse.

## Brown Dwarfs

Brown dwarfs are failed stars that are in-between stars and planets. Brown dwarfs are extremely dim and are impossible to see with the naked eye.

#### L-Type

*Main Article: L-Type Star*

L-Type brown dwarfs are cooler than M-Type stars, but not cool enough to be considered a planet. They are very dark red in color.

#### T-Type (Methane dwarfs)

*Main Article: T-Type Star*

T-Type brown dwarfs are brown dwarfs with much more methane in their atmosphere. Due to the amount of methane, T-Type dwarfs are almost scarlet/magenta in color, but darker than L-Type dwarfs.

#### Y-Type (Ultra-cool brown dwarfs)

*Main Article: Y-Type Star*

Y-Type brown dwarfs are very cool and dim. Y-Type dwarfs are very rare. A total of 17 objects are classified as a Y-Type dwarf as of August 2013. These brown dwarfs are almost black in color.

## Other Spectral Types

#### W-Type (Wolf-Rayet)

Wolf-Rayet stars are extremely massive and luminous stars, more luminous and massive than O-Type stars.

#### LBV-Type (Luminous blue variable)

LBV-Type stars are massive, rare and extremely luminous stars. They are also called S Doradus stars after S Doradus, one of the brightest stars in the Large Magellanic Cloud.

#### C-Type (Carbon Stars)

C-Type stars (carbon stars) are red giants near the end of their lives which contain a higher amount of carbon in their atmosphere than usual. Most carbon stars are giants or supergiants, very few main-sequence carbon stars are known.

#### S-Type

S-Type stars are a mix between M-Type stars and C-Type (carbon stars) stars. S-Type stars have large amounts of zirconium.

#### D-Type (White dwarf)

A D-Type (white dwarf) star is a stellar core remnant. A white dwarf is very dense, but slightly larger than Earth. White dwarfs have faint luminosity. No fusion takes place within a white dwarf. The closest white dwarf known is Sirius B, at 8.6 lightyears away.