It is important to notice that the meticulous observations of galactic clusters
stand out among the most promising strategies for understanding dark matter.
Unlike cold fronts on Earth, these systems are driven by the collision between galactic clusters
. Whenever a small cluster is pulled towards the core of a bigger one, the gravitational force between the two causes the gas in the core to move producing a spiral-shaped cold front.
For example, small differences in temperature across the sky show where parts of the universe were denser, eventually condensing into galaxies and galactic clusters
(Schekochihin and Cowley, 2008) have proposed a model for the fast growth of magnetic field in galactic clusters
using a self-accelerating dynamo.
Later chapters turn to the life-cycle of stars, the Milky Way galaxy, the varieties of galaxies beyond our own, and galactic clusters
. The last chapter reflects on "universal questions" and the search for life.
In a universe that never sits still, other galaxies orbit ours, and the Milky Way is on the move, too; our so-called Local Group of galaxies orbits its gravitational center, and also casts gravitational glances out to other galactic clusters
So some unseen mass must be at work, conventional wisdom declares, holding galactic clusters
together and governing the rotation rate of matter at the outer edges of individual galaxies.
As an alternative approach, quantum celestial mechanics (QCM) predicts that galactic clusters
are in quantization states determined solely by the total baryonic mass of the cluster and its total angular momentum.
The stars embedded in the nebula went unnoticed as a true cluster until 1931, when Per Collinder published his seminal paper, "On Structural Properties of Open Galactic Clusters
and their Spatial Distribution." Today the cluster carries the name Collinder 72 (Cr 72), but don't bother looking for it on any popular star atlas.
USA: Astronomers have captured images of the oldest and most distant galactic clusters
ever seen - a discovery that shows immense numbers of stars formed less than two billion years after the birth of the cosmos.
Current observations suggest that galactic clusters
, which consist of thousands of galaxies, reside in regions where the density of dark matter is higher than the average.
Only in the past 10 years have other observations, in fact, revealed that the thin gas permeating massive galactic clusters
is heated to tens of millions of degrees.