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Star formation feedback (stellar feedback), often shortened to feedback, likely was coined for star formation (SF) slowing itself down, a type of negative feedback. Stars in the process of forming and young stars push gas away, thus reducing interstellar medium (ISM) density and reducing star formation. However, the meaning of feedback in astrophysics seems to have shifted, now used for the outward movement of the gas, momentum, and energy (including EMR) back out into an object's surrounding space ("feeding it back"), and the term is used even in cases where the gas movement is not the consequence of the star formation itself.
Especially hot stars, including pre-main-sequence stars, as well as early stars that exist in very young stellar associations, produce stellar winds, and ionizing radiation, an outflow of energy that heats surrounding molecular clouds, leading to the cloud's expansion. This is opposite the mechanism of star formation (the contraction of such clouds) and the net consequence is a long-term limit on the star formation rate (SFR): if it rises above some level, it will subsequently fall, possibly to none, taking some time to resume.
The term feedback is also used for such outflows from galaxies and galaxy nuclei (galaxy feedback, AGN feedback, quasar feedback) and supernovae (SN feedback), which can similarly affect the ISM and slow down star formation (thus affecting galaxy's own evolution as well) as well as affect the intergalactic medium/intracluster medium. For AGNs, the feedback includes jets. Stellar feedback refers to such outflows from stars: stellar wind, radiation pressure, and photoheating, and likely can be meant to include SN feedback, the latter of which is also associated with young, hot stars.
Such feedback (outflows) from many stars can lower the SF rate of the whole galaxy for a time, after which gravity might draw back the expelled gas and the SFR again rises. For outflows from stars themselves, this can form a cycle. Such feedback can also enhance star formation: the push on ISM can increase the density, triggering SF in regions where conditions are such as to produce little simultaneous temperature-increase. A single instance of feedback may increase SF in some locations and decrease it in others.
Emission lines within a galaxy (e.g., emission line galaxies) can be a sign of feedback within it. With sufficient heating, e.g., from supersonic jets, excitation and ionization can result, with the subsequent relaxation leading to emission lines. This can be useful for determining the star formation of some very distant galaxies.