NASA
Glossary · Galaxies & Cosmology
Spiral, elliptical and irregular
The three basic shapes galaxies come in, and roughly what they mean.
Spirals have a rotating disc, arms full of gas and continuing star formation; ellipticals are pressure-supported blobs of old red stars with little gas and little new formation; irregulars are neither, usually small or recently disturbed. The sequence is not evolutionary in the way Hubble first guessed, but shape does encode history: ellipticals are widely thought to be the result of major mergers, which destroy discs and use up gas quickly.
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Related terms
Fast radio burst
A millisecond flash of radio energy from another galaxy, cause still unsettled.
Redshift
The stretching of light from distant objects, and the universe's odometer.
Hubble tension
Two good measurements of the universe's expansion rate that stubbornly disagree.
Dark energy
The name for whatever is making the expansion of the universe speed up.
Questions
What is Spiral, elliptical and irregular?
The three basic shapes galaxies come in, and roughly what they mean.
Why does it matter?
Spirals have a rotating disc, arms full of gas and continuing star formation; ellipticals are pressure-supported blobs of old red stars with little gas and little new formation; irregulars are neither, usually small or recently disturbed. The sequence is not evolutionary in the way Hubble first guessed, but shape does encode history: ellipticals are widely thought to be the result of major mergers, which destroy discs and use up gas quickly.