Star formation rate

Star formation rate is the mass of gas converted into stars per unit time. It measures how rapidly a galaxy or a region within it builds stellar populations.

Initial mass function: The distribution of stellar masses at birth in a population of newly formed stars. Rate estimates infer total stellar mass from luminous stars by assuming a distribution of stellar birth masses.
Star formation: The process by which dense regions of gas and dust collapse to form stars. The rate quantifies how quickly this broader process converts gas into stars.
Starburst galaxy: A galaxy forming stars at an exceptionally high rate relative to its gas supply or typical galaxies. Its elevated rate marks a short-lived episode of unusually rapid stellar growth.
Dust attenuation: The dimming and reddening of light as dust absorbs and scatters radiation. Uncorrected attenuation makes ultraviolet and optical tracers underestimate recent star formation.
H II region: A region of ionized hydrogen surrounding young, hot stars. Its emission traces ionizing radiation from massive stars formed within roughly the past few million years.
Molecular cloud: A cold, dense interstellar cloud composed mainly of molecular hydrogen and dust. These clouds provide the immediate raw material for most stars in nearby galaxies.
Main sequence of star-forming galaxies: The observed relation between stellar mass and star formation rate for actively star-forming galaxies. It provides a baseline for deciding whether a galaxy's rate is ordinary or enhanced.
Active galactic nucleus: A compact, luminous galactic center powered by accretion onto a supermassive black hole. Its radiation can mimic or contaminate emission used to estimate a galaxy's rate.
H-alpha: A visible hydrogen emission line with a wavelength of 656.3 nanometers. H-alpha luminosity is a widely used tracer of recent massive-star formation.
Molecular hydrogen: A molecule consisting of two hydrogen atoms, abundant in cold interstellar gas. Its distribution is commonly used to estimate the gas reservoir available for star formation.

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