Active Galactic Nucleus

An active galactic nucleus (AGN) is a region at the center of a galaxy that emits a significant amount of radiation and displays strong variability in its emission properties. This phenomenon is thought to be caused by the accretion of material onto a supermassive black hole located at the center of the galaxy. As material falls into the black hole, it heats up and emits radiation across the…

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Universe

The universe is a vast and complex system of galaxies, stars, planets, and other celestial bodies. It is estimated to be approximately 13.8 billion years old and spans an estimated 93 billion light-years in diameter. The universe is believed to have begun with a massive explosion called the Big Bang, which occurred approximately 13.8 billion years ago. At the time of the Big Bang, the universe…

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Big Bang

The Big Bang theory is the prevailing scientific explanation for the origin and evolution of the universe. According to this theory, the universe began as a singularity, a point of infinite density and temperature, approximately 13.8 billion years ago. At the time of the Big Bang, the universe was extremely hot and dense, and rapidly expanded and cooled over time. As it expanded, it cooled,…

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How might our universe end ?

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Galactic cluster Abell 2104

Abell, George O. (1927–1983) American AstronomerGeorge O. Abell is best known for his investigation and classification of galactic clusters. Using photographic plates from the Palomar Observatory Sky Survey (POSS) made with the 1.2-m (48-inch) Schmidt Telescope at the Palomar Observatory in California, he characterized more than 2,700 Abell clusters of galaxies. In 1958 he summarized this work in a book now known as the Abell Catalogue.Abell cluster A rich (high-concentration density) cluster of galaxies as characterized by the American astronomer GEORGE O. ABELL (1927–83). In 1958 Abell produced a catalog describing over 2,700 of such high-density galactic clusters using photographic data from the Palomar Observatory. Abell required that each cluster of galaxies satisfy certain criteria before he included them in this catalog. His selection criteria included population (each Abell cluster had to contain 50 or more galaxies) and high-concentration density (richness). Abell also characterized such rich galactic clusters by their appearance—listing them as either regular or irregular.

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