galaxies

GALAXIES

Gravitationally bound system of stars and stellar remnants, gas and dust, and dark matter. Can also contain star clusters, multiple star sysems, and interstellar clouds

Dwarf galaxies have about ten million stars Giants have 1 trillion stars

Catagorized by shape or visual morphology

-A common form is the elliptical galaxy, which has an ellipse-shaped light profile. -Spiral galaxies are disk-shaped assemblages with curving, dusty arms. -Galaxies with irregular or unusual shapes are known as peculiar galaxies, typically result from disruption by the gravitational pull of neighboring galaxies. Such interactions between nearby galaxies, may ultimately result in galaxies merging, may induce episodes of significantly increased star formation, producing what is called a starburst galaxy. -Small galaxies that lack a coherent structure could also be referred to as irregular galaxies

Theoretically, more than 100 billion in observable universe

Most are 1,000 to 100,000 parsecs in diameter and are usually separated by distances on the order of millions of parsecs

Intergalactic space (the space between galaxies) is filled with a tenuous gas of an average density less than one atom per cubic meter

90% of galaxies are theoretically dark matter Many, if not all galaxies have a super massive blackhole in the center of it.

Elliptical Galaxies: elliptical shape Low star production Giant ellipticals are the largest galaxies somtime are caused by galaxies colliding and result in a starburst galaxy.

Spirals: Spiral galaxies consist of a rotating disk of stars and interstellar medium, along with a central bulge of generally older stars. An //Sa// galaxy has tightly wound, poorly defined arms and possesses a relatively large core region. //Sc// galaxy has open, well-defined arms and a small core region

A majority of spiral galaxies have a linear, bar-shaped band of stars that extends outward to either side of the core, then merges into the spiral arm structure

Our own galaxy is a large disk-shaped barred-spiral galaxy about 30 kiloparsecs in diameter and a kiloparsec in thickness. It contains about two hundred billion (2×1011) stars and has a total mass of about six hundred billion (6×1011) times the mass of the Sun