disk population

astronomy

Also known as: disc population

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June 25, 2026

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The "disk population" in astronomy refers to a component of spiral galaxies, including our own Milky Way Galaxy. This component is characterized by its flat structure, with a thickness roughly one-fifth of its diameter. The stars within the disk exhibit a radial distribution that decreases exponentially outward from the galactic center.1

This disk population is primarily composed of younger stars and is concentrated in the plane of the galaxy. It includes objects like open star clusters, O and B stars, Cepheid variables, emission nebulae, and neutral hydrogen. In contrast, Population II stars, which are older and more spread out, are found in the galactic halo and bulge. The disk population is also distinguished by its chemical composition, generally having a higher abundance of heavy elements compared to Population II stars.23

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planetary nebula
Positions in the Galaxy
…distribution often called a “disk population,” to distinguish them from the Population II (very old) and Population I (young) objects proposed by the German American astronomer Walter Baade. There is a wide variation in the ages of planetaries, and some are very young objects.
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…distribution often called a “disk population,” to distinguish them from the Population II (very old) and Population I (young) objects proposed by the German American astronomer Walter Baade. There is a wide variation in the ages of planetaries, and some are very young objects.
Read More

Milky Way Galaxy
Principal population types
…were placed in the “disk population.” Similarly, long-period variables were divided into different subgroups, such that those with periods of less than 250 days and of relatively early spectral type (earlier than M5e) were considered “intermediate Population II,” whereas the longer period variables fell into the “older Population I”…
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…were placed in the “disk population.” Similarly, long-period variables were divided into different subgroups, such that those with periods of less than 250 days and of relatively early spectral type (earlier than M5e) were considered “intermediate Population II,” whereas the longer period variables fell into the “older Population I”…
Read More