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We explore the qualitative changes that would occur if the amplitude Q ∼ 10 −5 of cosmological density fluctuations were different. If Q ∼ < 10 −6 , the cosmological objects that form would have so low virial temperatures that they may be unable to cool and form stars, and would be so loosely bound that even if they could produce a supernova explosion, they(More)
Observations of early afterglow emission from gamma-ray bursts (GRB's) with the Swif t satellite show steep decay of the X-ray light curve, F ν (t) ∝ t −α with α ≈ 2.5 − 4 at ∼ 300 − 500 s after the burst trigger. The spectrum in this time interval is consistent with a spectrum F ν ∝ ν −β with β ≈ 1. Here, we show that these results can be explained as due(More)
We describe a mechanism by which supermassive black holes can form directly in the nuclei of protogalaxies, without the need for " seed " black holes left over from early star formation. Self-gravitating gas in dark matter halos can lose angular momentum rapidly via runaway, global dynamical instabilities, the so-called " bars within bars " mechanism. This(More)