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Size (left) and distance (right) of a few well-known galaxies put to scale. There are an estimated 100 billion galaxies in all of the observable universe. [1] On the order of 100,000 galaxies make up the Local Supercluster, and about 51 galaxies are in the Local Group (see list of nearest galaxies for a complete list).
In 2016, the International Astronomical Union (IAU) organized a Working Group on Star Names (WGSN) [2] to catalog and standardize proper names for stars. The WGSN's first bulletin, dated July 2016, [3] included a table of 125 stars comprising the first two batches of names approved by the WGSN (on 30 June and 20 July 2016) together with names of stars adopted by the IAU Executive Committee ...
Many galaxies are thought to have black holes at their active centers. The Milky Way's central black hole, known as Sagittarius A* , has a mass four million times greater than the Sun. As of March 2016, GN-z11 is the oldest and most distant observed galaxy with a comoving distance of 32 billion light-years from Earth, and observed as it existed ...
Radio-faint galaxies like M 31 and M33, the Milky Way's neighbors, have weaker fields (about 5 μG), while gas-rich galaxies with high star-formation rates, like M 51, M 83 and NGC 6946, have 15 μG on average. In prominent spiral arms, the field strength can be up to 25 μG, in regions where cold gas and dust are also concentrated.
[110] [111] [112] Most stars are within galaxies, but between 10 and 50% of the starlight in large galaxy clusters may come from stars outside of any galaxy. [113] [114] [115] A multi-star system consists of two or more gravitationally bound stars that orbit each other. The simplest and most common multi-star system is a binary star, but ...
The physical universe is defined as all of space and time [a] (collectively referred to as spacetime) and their contents. [10] Such contents comprise all of energy in its various forms, including electromagnetic radiation and matter, and therefore planets, moons, stars, galaxies, and the contents of intergalactic space.
The following is a list of particularly notable actual or hypothetical stars that have their own articles in Wikipedia, but are not included in the lists above. BPM 37093 — a diamond star Cygnus X-1 — X-ray source
Stellar dynamics involves determining the gravitational potential of a substantial number of stars. The stars can be modeled as point masses whose orbits are determined by the combined interactions with each other. Typically, these point masses represent stars in a variety of clusters or galaxies, such as a Galaxy cluster, or a Globular cluster.