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Virtually all massive galaxies host central black holes, the growth of which releases vast amounts of energy that powers quasars and other weaker active galactic nuclei. However, a tiny fraction of this energy could halt star formation by heating and ejecting ambient gas; a central question in galaxy evolution is the degree to which this process has caused the decline of star formation in large elliptical galaxies.
Observations of the Sun during total eclipses have led to major discoveries. A new generation of ground-based eclipse observations reaches spatial, temporal and spectral-resolution domains that are inaccessible from space.