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Main-sequence stars vary in surface temperature from approximately 2,000 to 50,000 K, whereas more-evolved stars – in particular, newly-formed white dwarfs – can have surface temperatures above 100,000 K. [3] Physically, the classes indicate the temperature of the star's atmosphere and are normally listed from hottest to coldest.
Almost every pixel seen in the image is a galaxy, each containing billions of stars. [1] Galaxy groups and clusters are the largest known gravitationally bound objects to have arisen thus far in the process of cosmic structure formation. [2] They form the densest part of the large-scale structure of the Universe.
There are actually only four galaxies in the compact group, the other galaxy is a foreground galaxy. The group is therefore more properly called HCG 92, because the name refers to a visual collection and not a group. Thus, the real group is also called Stephan's Quartet. Wild's Triplet
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).
5th century BC – Democritus proposes that the bright band in the night sky known as the Milky Way might consist of stars. 4th century BC – Aristotle believes the Milky Way to be caused by "the ignition of the fiery exhalation of some stars which were large, numerous and close together" and that the "ignition takes place in the upper part of the atmosphere, in the region of the world which ...
Star formation theory, as well as accounting for the formation of a single star, must also account for the statistics of binary stars and the initial mass function. Most stars do not form in isolation but as part of a group of stars referred as star clusters or stellar associations. [2]
The evolution of binary star and higher-order star systems is intensely researched since so many stars have been found to be members of binary systems. Around half of Sun-like stars, and an even higher proportion of more massive stars, form in multiple systems, and this may greatly influence such phenomena as novae and supernovae, the formation ...
The Local Group is the galaxy group that includes the Milky Way, where Earth is located. It has a total diameter of roughly 3 megaparsecs (10 million light-years ; 9 × 10 19 kilometres ), [ 1 ] and a total mass of the order of 2 × 10 12 solar masses (4 × 10 42 kg). [ 2 ]