s0

S0 is a designation used in different scientific fields to label distinct concepts that share the same alphanumeric form. In astronomy, S0 denotes a class of lenticular galaxies located in the Hubble sequence. S0 galaxies have a prominent central bulge and an extended disk but show little or no spiral structure and minimal current star formation. Their smooth light profiles and intermediate properties between ellipticals and spirals have led astronomers to regard them as transitional objects. They are common in galaxy clusters and groups, and their formation is a topic of ongoing study, with scenarios including fading from spiral morphology, minor mergers, and environmental effects.

In chemistry and spectroscopy, S0 denotes the electronic ground state of a molecule, a singlet state where the total spin S equals 0. This S0 designation corresponds to a singlet spin state with S = 0 and multiplicity 2S+1 = 1. The letter S stands for spin multiplicity, with the ground state labeled S0 and excited states labeled S1, S2, etc. Transitions between these states underpin many ultraviolet and visible absorption and emission processes and are central to molecular spectroscopy and photophysics.