Cooling Flow
As the ICM in the core of many galaxy clusters is dense, it emits a lot of X-ray radiation (the emission is proportional to the density-squared). In the absence of heating, the ICM should be cooling. As it cools, hotter gas will flow in to replace it. This is known as a cooling flow. The cooling flow problem is the lack of evidence of cooling of the ICM.
Read more about this topic: Intracluster Medium
Famous quotes containing the words cooling and/or flow:
“As a bathtub lined with white porcelain,
When the hot water gives out or goes tepid,
So is the slow cooling of our chivalrous passion,
O my much praised but-not-altogether-satisfactory lady.”
—Ezra Pound (1885–1972)
“Opinionated writing is always the most difficult ... simply because it involves retaining in the cold morning-after crystal of the printed word the burning flow of molten feeling.”
—Gavin Lyall (b. 1932)