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The universe's first stars, 30 to 300 times as massive as our Sun and millions of times as bright, would have burned for only a few million years before exploding as supernovae, sometimes producing black holes. The black holes would have swallowed gas and stars and become extremely bright "mini-quasars." The mini-quasars would have grown and merged to become the huge black holes found in the centers of galaxies. The supernovae would have spewed the chemical elements produced into their interiors into the gas around them. Webb will try to find and understand these supernovae and mini-quasars to put theories of early universe formation to the test. Scientists know that several million years after the Big Bang, the gas in the expanding universe became extremely cold. Gas made up of hydrogen atoms and molecules turned opaque to ultraviolet light. They also know, from viewing distant quasars, that about a billion years later, the gas became transparent again. For such a major change to have taken place, the hydrogen must have been reheated by a huge release of a energy. Webb will help establish when this reheating, or reionization, happened, and identify the sources of the reheating. |
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