metanolmaser

Metanolmaser, or methanol maser, is a naturally occurring microwave amplification by stimulated emission of radiation produced by methanol (CH3OH) molecules in interstellar environments. Methanol masers arise when population inversion occurs in methanol energy levels, producing bright, narrow spectral lines at specific frequencies. They are observed as compact, highly beamed emission with brightness temperatures far exceeding thermal values.

There are two main classes: class I methanol masers, pumped by collisions and typically associated with shocks in outflows or at the edges of expanding H II regions; class II methanol masers, pumped by infrared radiation from young, massive stars, and found close to hot molecular cores and ultra-compact H II regions. The most prominent class II line is at 6.7 GHz, followed by 12.2 GHz, among others; class I lines include 36 GHz and 44 GHz transitions.

Methanol masers are most commonly found in regions of high-mass star formation, often tracing early stages before the emergence of bright compact H II regions. They provide information on kinematics via Doppler-shifted lines and, with very long baseline interferometry, enable precise astrometry and parallax measurements, contributing to the mapping of Galactic structure. They are also observed in a smaller number of extragalactic sources, though less commonly than those in the Milky Way.

Observational properties include narrow linewidths, high brightness temperatures, and variability over time. The study of methanol masers informs models of maser pumping, molecular outflows, and the environmental conditions in star-forming regions.