Morphology

銀河はその見た目を指標に様々な形態に分類されています。１９３０年代にハッブルに提案された楕円銀河、渦巻銀河、棒渦巻銀河の３種類に分類する「ハッブル音叉図」が有名です。

銀河の光の分布をパラメータ化した「非対称性」等の”morphological parameters”も用いられます。

渦巻銀河は星形成が活発、楕円銀河は星形成が起きていない、非対称な銀河は衝突合体が直近で起きた可能性が高い等、銀河の形態は物理量や起きている物理過程についての情報等も与えてくれる指標です。

Galaxies are grouped into “morphologies” based on their visual appearance. A famous criteria is the “Tuning Fork Diagram” proposed by Edwin Hubble in the 1930s. In addition to visual appearance, “morphological parameters”, a set of statistics that parametrize the light distribution of galaxies, for example, asymmetry, are also used in morphological studies.

A galaxy’s morphology tells us not only about its appearance but also about its physical properties and physical processes taking place, for example, spiral galaxies having active star formation, elliptical galaxies having ceased star formation, asymmetric galaxies having indicators of recent merger events, etc.