= Messier 82
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= M82
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<Messier 82>, also called <M82>, is a nearby <starburst galaxy> used to study how intense <star formation> drives a large galactic outflow. Its bright stellar disk, obscuring <interstellar dust> and extended gas emission trace different components; a bright feature in one wavelength band need not represent most of the outflow's mass or energy.
A concrete measurement is to compare diffuse <X-ray> emission above the disk with compact sources inside it. ROSAT imaging and spectroscopy detected the wind's X-rays to roughly six <kiloparsecs> from the plane. The observations separated point sources from diffuse emission and found that the latter was not well described as a freely expanding wind: shocked material interacting with the flow could instead account for the emission.<ROSAT Observations of the Galactic Wind in M82 by Dave Strickland and others>[Abstract, spatial/spectral separation and comparison of wind models]{ref}
This makes <M82> an illuminating <stellar feedback> laboratory. The inference runs from spatially resolved spectra to gas conditions and then to a physical outflow model; a photograph of gas extending away from the disk does not by itself determine its temperature, energy source or escape rate.
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