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Abstract

We consider ever-expanding big bang models with a cosmological constant, ", and investigate in detail the evolution of the observable part of the universe. We also discuss quintessence models from the same point of view. A new concept, the "-sphere (or Q-sphere, in the case of quintessence) is introduced. This is the surface in our visible universe that bounds the region where dark energy dominates the expansion, and within which the universe is accelerating. We follow the evolution of this surface as the universe expands, and we also investigate the evolution of the particle and event horizons as well as the Hubble surface. We calculate the extent of the observable universe and the portion of it that can be seen at di †erent epochs. Furthermore, we trace the changes in redshift, apparent magnitude and apparent size of distant sources through cosmic history. Our approach is di †erent from, but complementary to, most other contemporary investigations, which concentrate on the past light cone at the present epoch. When presenting numerical results we use the FRW world model with and as our stan-) m0 \ 0.30 ) "0 \ 0.70 dard cosmological model. In this model the "-sphere is at a redshift of 0.67, and within a few Hubble times the event horizon will be stationary at a Ðxed proper distance of 5.1 Gpc (assuming All h 0 \ 0.7). cosmological sources with present redshift larger than 1.7 have by now crossed the event horizon and are therefore completely out of causal contact.

Mechanical feedback from active galactic nuclei in galaxies, groups and clusters

“…The AGN and radio hotspots are visible in both images. Complex structure, including cavities and the cocoon shock can be seen in the x-ray image (Smith et al 2002). Figures reproduced by permission of the AAS.…”

“…A rapidly inflating lobe can drive shocks into the gas, producing edges in x-ray surface brightness that have been observed in a number of objects (e.g. Jones et al 2002, Smith et al 2002, Kraft et al 2003, Machacek et al 2006. However, the typical division between internal energy in the lobes and mechanical work done on the ICM has yet to be assessed (estimates exist for some cases, e.g., Forman et al 2005.…”

Deuterated forms of H 3 + and their importance in astrochemistry

“…DCO + and N 2 D + ) which are crucial tracers of physical conditions in dense and cold regions of interstellar clouds (e.g. [16,17]), the so-called dense cores [18], within which stars and planets form [19,20]. If the H 2 number densities of dense cores exceed a few ×10 4 cm −3 , CO molecules begins to 'catastrophically' freeze-out on dust grains, significantly reducing the CO fractional abundance in the gas phase (e.g.…”

“…their deuterated forms [33,34], which have been found to maintain large abundances toward the CO-depleted regions of starless cores (e.g. [16,26]). Current chemical models inclusive of spinstate chemistry follow the time-dependent evolution of hundreds of species in the gas-phase and on the surface of dust grains (e.g.…”

A Plausible Model for the Galactic Extended Red Emission: Graphene Exposed to Far-ultraviolet Light

“…Extended red emission (ERE) has been observed in a wide range of circumstellar and interstellar environments; it is a broad feature in the spectral region of 500-1000 nm (full width 60-120 nm at half maximum) with the maximum at 600-800 nm (Cohen et al 1975;Mattila 1979;Witt & Schild 1985;Furton & Witt 1990Witt & Boroson 1990;Perrin & Sivan 1992;Sivan & Perrin 1993;Gordon et al 1998;Szomoru & Guhathakurta 1998;Darbon et al 2000;Smith & Witt 2002;Witt et al 2008). Despite numerous models proposed in recent decades, definitive identification of the carriers of ERE and the associated processes has not been established.…”