A low-mass → protostar deeply embedded in a
→ circumstellar dusty envelope and resulting from the
→ gravitational collapse of a dense
→ pre-stellar core.
This stage in the process of star formation occurs typically a few
104 years after the onset of the collapse. Class 0 protostars
represent the earliest stage of → young stellar objects.
The → spectral energy distribution (SED) of a
Class 0 object resembles a → blackbody
spectrum at a temperature below ~ 15-30 K,
peaking at → submillimeter wavelengths beyond
100 μm. The central protostar has not yet
acquired its final mass, since → accretion is still going on, and
the envelope (detected in submillimeter wavelengths)
is more massive than the central protostellar mass.
Moreover, these objects show powerful → bipolar
ejections of material in the form of
collimated → carbon monoxide (CO)→ outflows which distinguish them
from the pre-stellar phase of star formation.
The subsequent evolution of a Class 0 is a → Class I.
See also: → class; → zero.
