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Non-equilibrium Microwave Plasma for Efficient High Temperature Chemistry
Published on: August 1, 2017
Thermal Stability of Cold Clouds in Galaxy Halos
The Astrophysical Journal
|December 1, 1999
Summary
Cold, dense clouds of hydrogen and helium can form stable thermal equilibria if their mass is sufficient. These clouds could potentially constitute Galactic dark matter but may not survive from early cosmic epochs.
Area of Science:
- Astrophysics
- Cosmology
- Astrochemistry
Background:
- Investigating the thermal properties of cold, dense interstellar clouds composed of molecular hydrogen and atomic helium.
- Exploring the conditions under which solid or liquid hydrogen can exist within these clouds.
Purpose of the Study:
- To determine the thermal stability of cold, dense clouds under specific conditions.
- To assess the potential of these clouds to exist as dark matter in the Galactic halo.
Main Methods:
- Analysis of thermal properties, considering cloud mass, internal pressure, and cosmic-ray heating.
- Modeling of thermal continuum emission from solid or liquid hydrogen particles.
Main Results:
- Clouds with masses below 10^1.7 solar masses can maintain solid/liquid hydrogen at temperatures above the cosmic microwave background.
- Optically thin thermal emission can balance cosmic-ray heating, leading to stable thermal equilibria.
- A minimum mass of approximately 10^-6 solar masses is required for cloud survival in the Galactic disk.
Conclusions:
- These stable clouds could potentially represent a significant fraction of dark matter in the Galactic halo.
- The existence of such equilibria at high redshifts (z > 1) is unlikely due to a hotter cosmic microwave background.
- The formation and long-term survival of these clouds to the present epoch remain uncertain.
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