spiral galaxy

American  

noun

Astronomy.

1. a galaxy having a spiral structure.

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spiral galaxy British  

noun

1. a galaxy consisting of an ellipsoidal nucleus of old stars from opposite sides of which arms, containing younger stars, spiral outwards around the nucleus. In a barred spiral the arms originate at the ends of a bar-shaped nucleus

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spiral galaxy Scientific  

/ spī′rəl /

1. A galaxy consisting of a rotating flattened disk with an ellipsoidal central bulge from which extend a pattern of two or more luminous spiral arms. Spiral galaxies range from large bulges with tightly wound arms (classified as Sa) to small bulges with loosely wound arms (classified as Sc and in some cases Sd). The majority of the mass of a spiral galaxy is contained in its bulge, made up mostly of old stars, while the arms are composed mostly of younger stars and large amounts of interstellar gas and dust. A spherical, relatively dust-free region known as a galactic halo surrounding a spiral galaxy may contain large amounts of dark matter. The Milky Way is a spiral galaxy.

2. ◆ A spiral galaxy whose central bulge has the shape of a bar from whose ends the spiral arms emanate is called a barred spiral galaxy. About a third of spiral galaxies have this straight or lozenge-shaped bar of stars, gas, and dust extending out from the nucleus. Barred spiral galaxies are classified similarly to regular spirals, from SBa (large bulge, tightly wound arms) to SBc (smaller bulge, looser arms). Astronomers believe that some elliptical galaxies containing hints of a bar and spiral might once have been barred spiral galaxies.

3. See illustration at galaxy Compare elliptical galaxy irregular galaxy lenticular galaxy See more at Hubble classification system

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Etymology

Origin of spiral galaxy

First recorded in 1910–15

Example Sentences

In essence, Ivanov said, "It's the highest redshift, spectroscopically confirmed, unlensed barred spiral galaxy."

From Science Daily • Feb. 27, 2026

J0107a is a barred spiral galaxy just like the Milky Way.

From Space Scoop • Jun. 5, 2025

Our solar system is nestled on the third arm of the Milky Way, a spiral galaxy that is, yes, average: just one among 2 trillion galaxies in the universe.

From Slate • Feb. 7, 2025

Interstellar gas and dust coalesce in the rotation of a spiral galaxy, promoting star formation along its arms.

From New York Times • May 23, 2024

From our galaxy to the nearest spiral galaxy, M31, also in the constellation Andromeda, is 2,000,000 light-years.

From "Cosmos" by Carl Sagan