(ultraviolet photon with proper energy to excite molecular hydrogen)
A Lyman-Werner photon is an ultraviolet (UV) photon
in the H2 Lyman band (aka Werner band,
which can be absorbed by an H2 molecule,
pushing the molecule to an excited state,
possibility subsequently resulting in the molecule's dissociation,
i.e., splitting into atomic hydrogen.
UV in this band is called Lyman-Werner radiation (LW radiation)
or Lyman-Werner flux (LW flux).
In molecular clouds, this is the most common
means of photodissociation.
It is a means by which early stars counteract
cooling of molecular clouds, suppressing
star formation (star formation feedback) and has been of particular
interest in the modeling the formation of
Population III stars, given that
metallicity was very low, giving clouds a lower cooling rate,
making them less likely to reach the point of star formation.
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