ar X iv : a st ro - p h / 01 07 60 1 v 1 3 1 Ju l 2 00 1 Suppression of Gravitational Structure Formation by Cosmological Accretion Heating

ar X iv : a st ro - p h / 93 05 00 2 v 1 6 M ay 1 99 3 Visibility of Gravitational Lenses and the Cosmological Constant Problem

Recent observations suggest appreciable star formation activity in early-type galaxies down to redshift z ∼ 0.5. If so, there is likely to be dust in these galaxies. We consider the possibility that obscuration by dust can reconcile the observed frequency of gravitational lensing of quasar images with the considerably larger rate predicted in a low density cosmologically flat universe dominated...

ar X iv : a st ro - p h / 04 07 23 2 v 1 1 2 Ju l 2 00 4 B The Saas Fee Lectures on Strong Gravitational Lensing

ar X iv : a st ro - p h / 01 07 35 5 v 1 1 8 Ju l 2 00 1 Global star formation history : A Local Group perspective

The global star formation rate (SFR) density is estimated from the star formation histories (SFHs) of Local Group galaxies. This is found to be broadly consistent with estimates of the global SFH from existing redshift surveys for two favoured cosmologies. It also provides additional evidence for a relatively constant global SFR density at high redshift (z > 1).

ar X iv : a st ro - p h / 01 03 43 8 v 1 2 7 M ar 2 00 1 X - rays and accretion discs as probes of the strong gravity of black holes

The observations and interpretation of broad iron lines in the X-ray spectra of Seyfert 1 galaxies are reviewed. The line profiles observed from MCG–6-30-15 and NGC 3516 show extended red wings to the line explained by large gravitational red-shifts. The results are consistent with the emission expected from an X-ray irradiated flat accretion disc orbiting very close to a black hole. Results fr...

ar X iv : a st ro - p h / 01 04 11 3 v 1 6 A pr 2 00 1 1 / 2 Law for Non - Radiative Accretion Flow

At low densities, when radiation of an accreting gas is dynamically unimportant, quasi-spherical non-radiative accretion flow is formed around a compact object. We show that the density of the flow is n ∝ r −1/2. The gas compression is much weaker than the standard Bondi's, n ∝ r −3/2 , because most of the gas does not reach the compact object. It can either circulate indefinitely long or it ca...