Observing
As the ICM is so hot, it mostly emits X-ray radiation by the bremsstrahlung process and X-ray emission lines from the heavy elements. These X-rays can be observed using an X-ray telescope. Depending on the telescope, maps of the ICM can be made (the X-ray emission is proportional to the density of the ICM squared), and X-ray spectra can be obtained. The brightness of the X-rays tells us about the density of the gas. The spectra allow temperature and metallicity of the ICM to be measured.
The density of the ICM rises towards the centre of the cluster with a strong peak. In addition, the temperature of the ICM typically drops to 1/2 or 1/3 of the outer value in the central regions. The metallicity rises from the outer region towards the centre. In some clusters (e.g. the Centaurus cluster) the metallicity of the gas can rise above that of the sun.
Read more about this topic: Intracluster Medium
Famous quotes containing the word observing:
“No one can doubt, that the convention for the distinction of property, and for the stability of possession, is of all circumstances the most necessary to the establishment of human society, and that after the agreement for the fixing and observing of this rule, there remains little or nothing to be done towards settling a perfect harmony and concord.”
—David Hume (1711–1776)
“We were observing once to Mr. [Samuel] Crisp that the good and the agreeable were seldom united—”Ay begad,” cried he, “’tis rare enough to meet with the one or the other.””
—Frances Burney (1752–1840)
“No one can doubt, that the convention for the distinction of property, and for the stability of possession, is of all circumstances the most necessary to the establishment of human society, and that after the agreement for the fixing and observing of this rule, there remains little or nothing to be done towards settling a perfect harmony and concord.”
—David Hume (1711–1776)