12 research outputs found
The Race Between Stars and Quasars in Reionizing Cosmic Hydrogen
The cosmological background of ionizing radiation has been dominated by
quasars once the Universe aged by ~2 billion years. At earlier times (redshifts
z>3), the observed abundance of bright quasars declined sharply, implying that
cosmic hydrogen was reionized by stars instead. Here, we explain the physical
origin of the transition between the dominance of stars and quasars as a
generic feature of structure formation in the concordance LCDM cosmology. At
early times, the fraction of baryons in galaxies grows faster than the maximum
(Eddington-limited) growth rate possible for quasars. As a result, quasars were
not able to catch up with the rapid early growth of stellar mass in their host
galaxies.Comment: 5 pages, 1 figure, Accepted for publication in JCA
Primordial Structure of Massive Black Hole Clusters
We describe a mechanism of the primordial black holes formation that can
explain the existence of a population of supermassive black holes in galactic
bulges. The mechanism is based on the formation of black holes from closed
domain walls. The origin of such domain walls could be a result of the
evolution of an effectively massless scalar field during inflation. The initial
non-equilibrium distribution of the scalar field imposed by background
de-Sitter fluctuations gives rise to the spectrum of black holes, which covers
a wide range of masses -- from superheavy ones down to deeply subsolar. The
primordial black holes of smaller masses are concentrated around the most
massive ones within a fractal-like cluster.Comment: 19 pages; 3 figures; The final version accepted for publication in
Astroparticle Physic
'Disc-jet' coupling in black hole X-ray binaries and active galactic nuclei
In this chapter I will review the status of our phenomenological
understanding of the relation between accretion and outflows in accreting black
hole systems. This understanding arises primarily from observing the relation
between X-ray and longer wavelength (infrared, radio) emission. The view is
necessarily a biased one, beginning with observations of X-ray binary systems,
and attempting to see if they match with the general observational properties
of active galactic nuclei.Comment: 28 pages, 15 figures, To appear in Belloni, T. (ed.): The Jet
Paradigm - From Microquasars to Quasars, Lect. Notes Phys. 794 (2009