Small galaxies {dwarf galaxy} with irregular shapes contain primordial matter, often atomic hydrogen. Dwarf galaxies do not form stars unless they undergo collision and have starbursts. After many collisions and starbursts, they become globular clusters.
Galaxies have groups {galactic cluster}|. Cluster has diameter 10 million light-years, has thousand galaxies, and has even dark-matter and hot-gas distribution. Hot gas radiates x-rays. In early universe, radiation energy was high compared to gravity, so mass fluctuations were small. Only later did mass differences increase with time. Over distances of 1,000,000,000 light-years, galaxy density varies by 1/10. At larger volumes, grouping decreases, so universe is homogeneous. Early galaxies clustered more than dark matter.
For x-ray emitting galactic clusters, temperature varies directly with mass.
Closest spiral galaxy is Andromeda galaxy or Messier 31, 2 x 10^6 light-years away and twice as large as Milky Way. Milky Way Galaxy and Andromeda Galaxy are in Local Group {galaxy group}, which contains 40 dwarf galaxies. Local Group is near edge of Virgo Cluster, which contains hundreds of galaxies. The Great Attractor is another large galaxy group, 200,000,000 light years diameter.
Colliding galaxies {radio galaxy}| can emit three times more radio waves than light waves.
Regular-size spiral galaxies {Seyfert galaxy} can emit 100 times more infrared radiation than normal galaxies, from small central nuclei filled with fast moving ions. They last only 10^8 years.
Galactic clusters form groups {supercluster}, with diameter 30,000,000 light-years. Superclusters form groups {wall}, with diameter 300,000,000 light-years. Walls do not appear to have groups. Great Wall is 200,000,000 light years away.
Luminous infrared galaxies {ultraluminous infrared galaxy} (ULIRG) were abundant among early galaxies.
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Date Modified: 2022.0225