Knowra Low surface brightness galaxy Low surface brightness galaxy A galaxy whose luminosity is spread over an unusually large apparent area, giving it low brightness per unit area and making it difficult to detect against the night sky.
Surface brightness : The apparent brightness of an extended object per unit area on the sky. It is the defining observable that distinguishes these galaxies from brighter objects.
Galaxy : A gravitationally bound system of stars, gas, dust, and dark matter. Low surface brightness describes a structural and observational class of galaxies.
Malin 1 : A giant low surface brightness spiral galaxy discovered in the 1980s. Its enormous, faint stellar disk became a landmark example of the class.
High surface brightness galaxy : A galaxy whose luminosity per unit area is relatively high. It represents the brighter, easier-to-detect counterpart to the class.
Missing satellite problem : The discrepancy between predicted numbers of small dark matter halos and observed satellite galaxies. Faint, diffuse systems may hide some galaxies absent from earlier counts.
Sky brightness : The brightness of the night sky, produced by natural and artificial light sources. Its background glow can overwhelm the faint light spread across a galaxy.
Luminosity : The total energy emitted by an object per unit time. A galaxy can have substantial total luminosity while spreading it across a large area.
Dragonfly 44 : An ultra-diffuse galaxy in the Coma Cluster studied for its unusually large inferred dark matter content. It illustrates how a faint galaxy can appear to contain far more mass than its stars suggest.
Ultra-diffuse galaxy : A galaxy with an unusually large size and very low surface brightness, often despite substantial stellar mass. This specific diffuse-galaxy class overlaps strongly with low surface brightness galaxies.
Galaxy formation : The processes by which gas, stars, and dark matter assemble into galaxies. Diffuse galaxies constrain how galaxies form and retain or lose their gas.
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