The energetic, scalable fabric of the universe

"Clusters of galaxies, the largest known gravitationally-bound objects, are the knots in the cosmic web of structure that permeates the Universe. Theoretical models make predictions about the number, distribution and properties of these clusters.

"Scientists can test and improve models of the Universe by comparing these predictions with observations. The most powerful way of doing this is to measure the masses of galaxy clusters, particularly those in the distant Universe. However, weighing galaxy clusters is extremely difficult [because where would you find a scale that big?].

"One relatively easy way to weigh a galaxy cluster is to use simple laws ('scaling relations') to estimate its weight from properties that are easy to observe, like its luminosity (brightness) or temperature. This is like estimating someone's weight from their height if you didn't have any scales.

"A team of researchers has observed 11 distant galaxy clusters with ESA's XMM-Newton and NASA's Chandra X-ray Observatory. The X-ray data allowed the scientists to measure the temperatures and luminosities of the gas in the clusters. They were then able to infer their total masses, which varied between 200 and 1,100 times the mass of our Milky Way galaxy.

"These measurements were then used to test whether galaxy clusters of different sizes and located at different distances from us are simply scaled versions of each other -- a condition known as being 'self-similar.' This is an important characteristic for astronomers to identify if they hope to get the true weights of galaxy clusters."