Clusters of Galaxies

The largest known objects in our Universe…

Local Supercluster

• The Local supercluster contains the Virgo cluster of galaxies as well as about 50 galaxy groups

Virgo cluster of galaxies

• The Virgo cluster of galaxies is about 65 million light years away• It contains about 2000 galaxies•It is dominated by M87

M87

Types of Galaxy Clusters

Regular clusters concentrated central core well-defined spherical structure size in the range 1-10 Mpc mass M ~ 10 Mo

Coma cluster

Irregular clusters no well-defined center similar size range mass 10 -10 Mo

Virgo cluster

Perseus Cluster

• One of the closest galaxy clusters at a distance of 300 million light years•Part of the Perseus Pisces supercluster which is 15 degrees across and has over 1000 galaxies

X-ray emission from Clusters

• Clusters of galaxies are virially bound by dark matter which is traced by hot gas• Mass of hot gas is more than 3 times the mass of the visible light galaxies in the Virgo cluster• X-rays are concentrated around M87

Virgo/ROSAT

Virgo Cluster in Visible/X-ray

Virgo/ROSAT

M87

X-ray emission from Clusters

• Clusters of galaxies are virially bound by dark matter which is traced by hot gas

NGC2300/ROSAT

Merging Clusters

• A2256 cluster has about 500 galaxies• It is about 10 million light years across• It is about 1 billion light years away• The 80 million degree gas is brightest in the center where two clusters are merging

Coma Cluster

• Coma cluster has about 1000 galaxies• It is located near the north galactic pole• It is about 300 million light years away• Large bright central cluster is merging with smaller galaxy group at the lower right

Small Cluster

• X-rays from this smaller cluster were discovered by ROSAT• Hot gas engulfs the two bright elliptical galaxies• It is about 500 million light years away

X-ray emission from Clusters

•Temperature profiles of X-ray emitting gas shows differences in cluster evolution•This cluster is almost isothermal (all one temperature) but is slightly cooler towards the outside of the cluster

Merging Clusters

•This cluster is not isothermal•It shows a very hot region indicating a shock formed where two galaxies in the cluster may have collided

Cannibal Cluster

• A3827 is about 1.5 billion light years away• The central dominant galaxy is eating five smaller galaxies

ESO/Optical

Very Distant Cluster

• This cluster is 8 billion light years away, so it formed when the universe was half its present age

Very Distant Cluster

• This is a very red cluster (Doppler Shift)• It is the most distant cluster discovered by HST• It may be too far away to have formed in a dense universe