Animation of cloud core with forming star MIRI can probe how cold cloud cores collapse into stars. This process has been hidden from us because of the immense optical depth of these cores, which blocks all the visible and near infrared emission from escaping.(animation from M. Ressler)

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Protostar drawing Protostar spectral energy distribution
Very young protostars – Class 0 – have been observed in the sub-mm but most are currently undetected in the IR (IRAS, ISO). They appear to be T~20K blackbodies from sub-mm observations.

The sub-mm energy distribution does not constrain the envelope density profile. The radial envelope density can inferred from sub-mm maps, but it is ambiguous due to T – density degeneracy.

Mid-IR SEDs of Class 0 objects are very sensitive to density distributions; MIRI data can constrain Class 0 radiative transfer at a resolution of 50 AU in the nearest sources.