Low surface brightness galaxy

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A low surface brightness galaxy, or LSB galaxy, is a diffuse galaxy with a surface brightness that, when viewed from Earth, is at least one magnitude lower than the ambient night sky.

Most LSBs are dwarf galaxies, and most of their baryonic matter is in the form of neutral gaseous hydrogen, rather than stars. They appear to have over 95%^{[citation needed]} of their mass as non-baryonic dark matter. There appears to be no supernova activity in these galaxies. It is estimated that 90% of all galaxies are LSB galaxies, not high-surface-brightness types. Currently around 3000 are catalogued (as of 2005^[update]).

Rotation curve measurements indicate an extremely high mass-to-light ratio, meaning that stars and luminous gas contribute only very little to the overall mass balance of an LSB. The centers of LSBs show no large overdensities in stars, unlike e.g. the bulges of normal spiral galaxies. Therefore they seem to be dark matter dominated even in their centers which makes them excellent laboratoried for the study of dark matter.

In comparison to the more well-studied high-surface brightness galaxies, LSBs are mainly isolated field galaxies, found in regions devoid of other galaxies. In their past, they had fewer tidal interactions or mergers with other galaxies, which could have triggered enhanced star formation. This is an explanation for the small stellar content.