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Galaxy Clusters

Images of distant galaxy clusters show fascinating diversity. The current theories for that diversity are lacking.

Nearly all galaxy clusters have a giant elliptical galaxy near its center.

Elliptical galaxies and globular clusters are similar. They don't spin or flatten but remain a very loose 'ball' of stars and maintain that shape over millions of years or more.The elliptical galaxy holds many, many more stars than the globular cluster.  There is another similar object called a dwarf spheroidal galaxy. This is essentially a diffuse globular cluster.

Globular cluster M10 is observed to follow a rough ellipse around the Milky Way, even passing through the galactic disk. In contrast, the billions of stars within a spiral galaxy are not observed to follow an ellipse, including our Sun with a 'disturbed' orbit. This observation leads to suggesting dark matter when stars with that observed motion do not move in an ellipse as expected in a spiral galaxy.Theory does not match observation.

The stars  in a globular or an elliptical are observed moving radially, in an oscillating linear motion relative to the center. This type of motion alternately in attraction and in repulsion must be electromagnetic.

DeepSkyVideos in youtube has 2 relevant videos: 1) M10 globular cluster orbit, 2) sausage globular clusters. 'sausage' is a reference to a plot of the motion data.

quotes are from Wikipedia.

Elliptical Galaxy:

Most elliptical galaxies are composed of older, low-mass stars, with a sparse interstellar medium and minimal star formation activity, and they tend to be surrounded by large numbers of globular clusters. Elliptical galaxies are believed to make up approximately 10%–15% of galaxies in the Virgo Supercluster, and they are not the dominant type of galaxy in the universe overall. They are preferentially found close to the centers of galaxy clusters.

The characteristics of elliptical galaxy are unique that you can distinguish them from the other galaxies (normal spiral, barred spiral, and irregular; a lenticular is a class between ellipticals and spirals). Elliptical has the dominant radial motion of stars. Moreover, the galaxy has the red color due to the presence of old stellar stars.

The smallest, the dwarf elliptical galaxies, may be no larger than a typical globular cluster.


The radial motion in an elliptical is also observed in globular clusters.

Dwarf Spheroidal Galaxy:

A dwarf spheroidal galaxy (dSph) is a term in astronomy applied to small, low-luminosity galaxies with very little dust and an older stellar population. They are found in the Local Group as companions to the Milky Way and to systems that are companions to the Andromeda Galaxy. While similar to dwarf elliptical galaxies in appearance and properties such as little to no gas or dust or recent star formation, they are approximately spheroidal in shape and generally have lower luminosity.

Despite the radii of dSphs being much larger than those of globular clusters, they are much more difficult to find due to their low luminosities and surface brightnesses.

Apparently a dwarf spheroidal galaxy is just a globular cluster but a larger volume for its stars results in its lower luminosity.

There is another rare galaxy type called a ring galaxy. This appears as a galactic core, or perhaps an elliptical, with a ring of stars around it. Hoag's Object is a good example.

Dr Becky in youtube has a video about Hoag's Object.

These descriptions imply this scenario:

a) nearly every large galaxy cluster has a large elliptical galaxy at its center.

b) Around that elliptical there will be a variety of other types, from a lenticular, which is essentially a spiral core with its halo and a dust lane but no arms, to a spiral (each having a different configuration of arms), to an irregular (which is many stars but with no defined structure like the other types).

c) Globular clusters proliferate in the cluster - around the elliptical and in smaller numbers around the other types but larger spirals generally have more globular clusters than smaller galaxies.

d) When looking at many galaxy clusters there is usually no apparent alignment pattern in the group.

Halton Arp observed sometimes quasars and BL LAC objects would align with the axis of a nearby active Seyfert, a very active spiral galaxy.

e) Even with so many 'clusters' of stars the galaxy cluster remains dispersed. When viewing many images of galaxy clusters a case where galaxies are seen to be merging are rare. Astronomers sometimes describe mergers and collisions but each case is usually a galaxy with an unusual appearance so with no other easy explanation available it is just described as an odd mix of others. A separation can look like a merge. The force of gravity is simply unable to collapse a cluster of galaxies holding billions or even trillions of stars, or even the much smaller globular clusters. More than just gravity is involved in a cluster's stability with the presence of electric fields capable of attraction or repulsion in a universe which is almost 100% plasma.

f) when jets or arcs are observed in a galaxy cluster the galaxy at their 'center' is usually a giant elliptical.

g) The observation that there is always a large elliptical galaxy at the center of every large galaxy cluster makes ellipticals rather critical in understanding how the universe evolves.

Some theories propose an elliptical is the result of a merger of spirals. The observed rotational motion of  stars in a spiral conflicts with radial motion of stars in ellipticals (and globulars). The observed presence of many intact globulars around an elliptical is difficult to explain after a collision or merger.

Galaxy clusters have no observed SMBH gobbling up as everything in 'reach' of it.

Each galaxy cluster is diverse, not collapsing.
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