Lurking at the centers of many galaxies, supermassive black holes make their presence known by gobbling gas, which heats up to fuel quasars and other fireworks. These so-called active galactic nuclei (AGN) are among the most luminous objects in the universe. Now astronomers say that they've found a new, relatively common class of AGN, so heavily smothered by gas and dust that virtually none of the visible and ultraviolet light generated within them can get out.
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