What Are The Types Of Galaxies?
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Galaxies come in three main types: spiral, elliptical, and irregular. Spirals (like the Milky Way and Andromeda) have rotating disks with arm structures. Ellipticals are smooth, oval-shaped, and contain mostly older stars. Irregulars don't fit either category. Edwin Hubble created this classification system in 1926.
Galaxies come in many shapes and sizes, but most fall into three main categories. Edwin Hubble created the classification system used today in 1926, dividing galaxies by their visual appearance. Spiral, elliptical, and irregular galaxies dominate the cataloged universe, with subtypes including barred spirals and lenticular galaxies. The differences relate to formation history and stellar content.
What is a spiral galaxy?
A flat, rotating disk with spiral arms. According to NASA, spiral galaxies have a central bulge of stars surrounded by a flat disk with arms of stars, gas, and dust winding outward. The arms are sites of ongoing star formation, containing many young, hot, blue stars. About two-thirds of spirals are subdivided as barred spirals, with a straight bar of stars cutting across the central bulge before the arms begin. Both the Milky Way and Andromeda are barred spirals. Scientists believe the presence of a bar indicates a galaxy has reached full maturity.
What is an elliptical galaxy?
An oval or spherical galaxy with little structure. Elliptical galaxies range from nearly spherical to highly elongated football shapes. Unlike spirals, ellipticals typically contain very little gas and dust, so they have little ongoing star formation. Their stars are generally older and orbit the galactic center in random directions rather than in an organized disk. Ellipticals are less common than spirals in the local universe but include some of the largest galaxies known. Scientists think elliptical galaxies often form from collisions and mergers between spiral galaxies.
What are irregular galaxies?
Galaxies that don't fit either main type. Irregular galaxies have no defined shape or structure. They often contain lots of gas and dust and active star formation, but lack the organized disk of spirals or the smooth shape of ellipticals. Many irregulars are small, but some are large. The two Magellanic Clouds, dwarf galaxies orbiting the Milky Way, are classic irregular galaxies. Many irregulars appear to have been disturbed by gravitational interactions with other galaxies, suggesting that mergers and tidal forces are common causes of irregularity.
What are active galaxies?
Galaxies with extraordinarily bright central regions. Active galaxies have central supermassive black holes that are actively consuming matter, producing far more radiation than normal galaxies. Active galaxies are subdivided into Seyfert galaxies, blazars, radio galaxies, and quasars (the most luminous). Most galaxies appear to have supermassive black holes at their centers, but most are quiet today because their black holes have run out of nearby material to consume. Active galaxies were much more common in the early universe, when there was more gas to feed black holes.
Galaxies come in three main types: spiral (including barred spirals), elliptical, and irregular. Spirals have rotating disks with arms of star formation, ellipticals are smooth and dominated by old stars, and irregulars lack defined shape. Active galaxies and quasars are subtypes with bright central regions powered by feeding supermassive black holes. Edwin Hubble created the classification system in 1926, and it remains the foundation of galactic morphology today.
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