Black Holes, Quasars, and Active Galaxies _ ESA_Hubble _ ESA_Hubble.pdf

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11/3/2019Black Holes, Quasars, and Active Galaxies | ESA/Hubble | ESA/Hubble1/3()The disk of dust and gas accreting around a 300million solar-mass black hole in NGC 7052.()Black holes, quasars and active galaxiesBlack holes are objects so dense, and with so muchmass, that even light cannot escape their gravity.The existence of black holes has been theorised formore than 200 years. It is impossible to observe themdirectly, and astronomers had no way to test theirtheories until Hubble arrived.The high resolution of Hubble made it possible to seethe e±ects of the gravitational attraction of some ofthese objects on their surroundings. Hubble has alsoproved that super massive black holes are most likelypresent at the centres of most, if not all, largegalaxies(). This has important implications for the theories ofgalaxy formation and evolution.Black holes exist in di±erent sizes. Stellar black holes, which are around the mass of our Sun, form when verylarge stars explode as supernovae at the end of their lives. The star's core collapses as the outer layers areblown away, leaving a small but extremely dense ball.Supermassive black holes, many millions of times the mass of our Sun, are of more mysterious origin, and arefound at the centre of galaxies. It is in the study of super massive black holes that Hubble has made its biggestcontribution.Black holes and the quasar connectionBefore Hubble, quasars were considered to beisolated star-like objects of a mysterious nature.

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Black Holes, supermassive black hole, Quasar, Active Galactic Nucleus

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