spiral galaxy

noun

, Astronomy.

1. a galaxy having a spiral structure.

spiral galaxy

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

spiral galaxy

/ 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 galaxyCompare elliptical galaxySee more at Hubble classification system

Word History and Origins

Origin of spiral galaxy¹

First recorded in 1910–15

Example Sentences

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

From New York Times

The mass of the black hole is also correlated to the stellar mass of a spiral galaxy's central bulge, or the overall mass of an elliptical galaxy.

From Scientific American

Euclid’s view of the nearby spiral galaxy IC 342 highlights the telescope’s piercing gaze.

From Scientific American

The telescope snapped pictures of a relatively close spiral galaxy that is a ringer for our own Milky Way.

From Seattle Times

Prior to their venture, they were once two normal massive stars that formed a binary system in their home spiral galaxy.

From Science Daily