Definition

Noun: A spiral galaxy is a type of galaxy characterized by a flat, rotating disk of stars, gas, and dust, with a central concentration of older stars (the bulge) and luminous spiral arms that extend outward. These arms contain younger stars, star clusters, and nebulae, and appear to wind out from the central region.

Usage

The term is used in astronomy to classify and describe a major category of galaxies based on their distinct structural morphology. - The Milky Way, our home galaxy, is a classic example of a spiral galaxy. - Astronomers used the telescope to study the spiral arms of the distant spiral galaxy.

Advanced Usage

• Barred Spiral Galaxy: A subtype of spiral galaxy featuring a central bar-shaped structure composed of stars, from which the spiral arms emanate.
  • NGC 1300 is a well-known barred spiral galaxy.

Variants and Related Words

• Spiral Nebula (historical term): An archaic term once used for spiral galaxies before their extragalactic nature was confirmed.
• Galaxy: The general category of massive, gravitationally bound systems of stars, stellar remnants, interstellar gas, dust, and dark matter.

Synonyms

• Spiral Nebula (historical context)
• Disc Galaxy (broader term, can include lenticular galaxies)

Related Phrases / Compound Terms

• Spiral Arm: One of the curved structures extending from the center of a spiral galaxy.
• Galactic Bulge: The central, spheroidal concentration of stars in a spiral galaxy.

Noun

1. a galaxy having a spiral structure; arms containing younger stars spiral out from old stars at the center