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Paper: Galaxy Formation: the First 109 Years
Volume: 380, At the Edge of the Universe: Latest Results from the Deepest Astronomical Surveys
Page: 17
Authors: Silk, J.
Abstract: Progress has been made in understanding the origin of spiral galaxies, but elliptical galaxy formation continues to pose many problems. At the centres of ellipticals, one finds supermassive black holes which are occasionally fed by gas accretion from their surroundings and are visible as active galactic nuclei. Negative feedback, due to the outflow from the central black hole during its active phase, terminates the gas supply to the spheroid, thereby resulting in an old stellar population. A contemporaneous phase of positive feedback when the protogalaxy is forming could result in the highly efficient phase of early star formation required by the recent data.
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