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Galaxies:  1 | 2

A galaxy is a system of millions or billions of stars, together with gas and dust, held together by gravity and isolated from similar systems by vast regions of space. They are classified by their shape. The three main types are elliptical, irregular, and spiral.

Elliptical

These galaxies have little to no structure, rotation, or interstellar matter. This results in minimal star formation and a dominance of long-lived, red stars. Ellipsoid collections of stars are the most common type of galaxy.

Irregular

Galaxies with an irregular shape are considered to be the result of collisions between galaxies. As a result, they generally contain a complex mix of interstellar dust and gas, young stars, and old stars.

Lenticular

A lenticular galaxy is a type of galaxy which is intermediate between an elliptical galaxy and a spiral galaxy in galaxy morphological classification schemes. A lenticular galaxy has a central bulge surrounded by a flattened disk, but without a pattern of spiral arms.

Spiral

These galaxies are disc-shaped with either a round, central hub (unbarred), or a hub shaped like a bar (barred). They rotate with spiral arms that contain interstellar dust and gas, promoting star formation and an abundance of young stars. Many galaxies reside in groups that are gravitationally bound together, including our own Milky Way, which is part of the Local Group. Sometimes gravity makes galaxies collide and eventually merge into one single galaxy. There is strong evidence that the Milky Way is a galaxy that has absorbed numerous smaller galaxies during its lifetime, inheriting their stars in the process.

Starburst

A starburst galaxy is one which is experiencing an episode of intense star formation, usually at its core. Starburst galaxies form stars at a rate ranging from ten to a hundred times faster than those of ordinary galaxies. Although the areas undergoing this accelerated rate of star formation are relatively small compared to the overall size of their home galaxies, starbursts significantly alter their environment by producing very massive and luminous stars. Starbursts are fueled by an over-abundance of interstellar gas, mostly in the form of hydrogen. An example of a starburst galaxy is Messier 82, also known as the Cigar Galaxy.

NGC 1132, an elliptical galaxy NGC 1569, an irregular galaxy NGC 3115, a lenticular galaxy NGC 5194, a spiral galaxy NGC 1398 M82, a starburst galaxy Spiral galaxy, NGC 224

Elliptical

Irregular

Lenticular

Spiral

NGC 1398

Messier 82

Andromeda Galaxy

The Milky Way Types of galaxies

Our galaxy, The Milky Way

Types of galaxies

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