Cooling flow
A cooling flow occurs when the
In a steady state, the rate of mass deposition, i.e. the rate at which the plasma cools, is given by
where L is the bolometric (i.e. over the entire spectrum) luminosity of the cooling region, T is its temperature, k is the Boltzmann constant and μm is the mean molecular mass.
Cooling flow problem
It is currently thought that the very large amounts of expected cooling are in reality much smaller, as there is little evidence for cool X-ray emitting gas in many of these systems.[2] This is the cooling flow problem. Theories for why there is little evidence of cooling include[3]
- Heating by the central Virgo clusters)
- Thermal conduction of heat from the outer parts of clusters
- Cosmic ray heating
- Hiding cool gas by absorbing material
- Mixing of cool gas with hotter material
Heating by AGN is the most popular explanation, as they emit a lot of energy over their lifetimes, and some of the alternatives listed have theoretical problems.
References
Further reading
- Qin, Bo; Wu, Xiang-Ping (2001-07-19). "Constraints on the Interaction between Dark Matter and Baryons from Cooling Flow Clusters". Physical Review Letters. 87 (6): 061301. S2CID 13510283.
- Chuzhoy, Leonid; Nusser, Adi (2006-07-10). "Consequences of Short-Range Interactions between Dark Matter and Protons in Galaxy Clusters". The Astrophysical Journal. 645 (2): 950–954. S2CID 16131656.
- 5.7. Cooling flows and accretion by cDs (in X-ray Emission from Clusters of Galaxies. Sarazin 1988)