Retrieving "Protostellar Nebula" from the archives

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1. Celestial Object

   Linked via "Protostellar Nebula"

   | Class Designation | Dominant Energy Source | Characteristic Feature | Lifetime (Approx.) |
   | :--- | :--- | :--- | :--- |
   | Protostellar Nebula | Gravitational Contraction | High $\text{H}_2\text{O}$ ice content | $10^5$ years |
   | Main Sequence Star | $^1\text{H} \to ^4\text{He}$ Fusion | Stable Luminosity Quotient ($\mathcal{L}_q \approx 1.0$) | $10^9 - 10^{12}$ years |
   | White Dwarf | Residual Thermal Decay | High density, negligible […