Martin J. Rees

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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)
We study the expected distribution of massive black hole (MBH) spins and its evolution with cosmic time in the context of hierarchical galaxy formation theories. Our model uses Monte Carlo realizations of the merger hierarchy in a ΛCDM cosmology, coupled to semi-analytical recipes, to follow the merger history of dark matter halos, the dynamics of the MBHs(More)
We investigate the ability of primordial gas clouds to retain molecular hydrogen (H 2) during the initial phase of the reionization epoch. We nd that before the Strr omgren spheres of the individual ionizing sources overlap, the UV background below the ionization threshold is able to penetrate large clouds and suppress their H 2 abundance. The consequent(More)
In hierarchical models of structure formation, an early cosmic UV background (UVB) is produced by the small (T vir ∼ < 10 4 K) halos that collapse before reionization. The UVB at energies below 13.6eV suppresses the formation of stars or black holes inside small halos, by photo–dissociating their only cooling agent, molecular H 2. We self–consistently(More)
Collapsed objects have definitely been observed: some are stellar-mass objects, the endpoint of massive stars; others, millions of times more massive, have been discovered in the cores of most galaxies. Their formation poses some still-unanswered questions. But for relativists the key question is whether observations can probe the metric in the strong-field(More)