The Giants of the Universe Mature Rapidly

An international team of astronomers, in a research led by an astromer of the INAF-OATs, has determined the detailed internal dynamics of distant clusters of galaxies, 8 billion years ago in cosmic history, when the Universe was 5,5 billion years old.
Clusters of galaxies are the giants of the Universe. These objects are the largest gravitationally bound structures in the Universe, containing hundreds or even thousands of galaxies orbiting the common center of mass in gravitational equilibrium. Being so large, clusters are predicted to form relatively late in the cosmic history, according to our current theoretical understanding. Observations indicate that the first clusters form 3 billions year after the Big Bang.

The clusters targeted by the new observations should be 2,5 billions year old; this is only 1/5 the age of the clusters observed in the nearby Universe. The team determined the mass profiles of these clusters, and the orbital shapes of the galaxies inside these clusters.
The rather unexpected result of the dynamical analysis was that these young giants of the universe look very similar to their old descendants in the nearby Universe. So clusters of galaxies reach a stable dynamical configuration quite early in their history, even if they continue to grow larger with time.
As a comparison, it is like completing a medical check-up of a teenager, and finding out that the the young man has already the physical structure of an adult, that (s)he will mantain for the rest of his life.
Based on data of the GOGREEN survey conducted at the Gemini telescopes (principal investigator: Michael Balogh, Univ. of Waterloo, Canada).


The spectra of all galaxies in the survey are shown together, as a function of observed frame wavelength.  Galaxy clusters (labelled) are easily spotted as spectra with similar features that line up vertically.



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