Groups and clusters of galaxies

Groups of galaxies are the smallest aggregates of galaxies. They typically have the following properties.

• They contain less than 50 galaxies.
• They have a diameter of about 2 Mpc.
• Their mass is approximately 10¹³ solar masses.
• The spread of velocities for the individual members is about 150 km/s.

Clusters are larger than groups. They typically have the following properties.

• They contain 50 to 1000 members.
• They have masses between 10¹⁴ to 10¹⁵ solar masses.
• They have a typically diameter of 8 Mpc.
• The spread of velocities for the individual members is about 800-1000 km/s.
• The average separation from other clusters is approximately 10 Mpc.

A list of some close groups and clusters of galaxies.

• Local Group
• Maffei Group
• Sculptor Group
• M81 Group
• NGC 5128 Group
• Canes I Group
• NGC1023 Group
• M101 Group
• Leo I Group
• Canes II Group
• Virgo Cluster
• Fornax Cluster