Oswaldo Duarte Miranda

Seed magnetic Fields Generated by Primordial Supernova Explosions

The origin of the magnetic field in galaxies is an open question in astrophysics. Several mechanisms have been proposed related, in general, with the generation of small seed fields amplified by a dynamo mechanism. In general, these mechanisms have difficulty in satisfying both the requirements of a suffici ently high strength for the magnetic field and the necessary large coherent scales. We show that the formation of dense and turbulent shells of matter, in the multiple explosion scenario of Miranda and Opher (1996, 1997) for the formation of the large-scale structures of the Universe, can naturally act as a seed for the generation of a magnetic field. During the collapse and explosion of Population III objects, a temperature gradient not parallel to a density gradient can naturally be established, producing a seed magnetic field through the Biermann battery mechanism. We show that seed magnetic fields � 10 12 10 14 G can be produced in this multiple explosion scenario on scales of the order of clusters of galaxies (with coherence length L � 1.8Mpc) and up to � 4.5 × 10 10 G on scales

Gravitational wave background from Population III black hole formation

We study the generation of a stochastic gravitational wave (GW) background produced from a population of core-collapse supemovae, which form black holes in scenarios of structure formation. We obtain, for example, that the formation of a population (Population III) of black holes, in cold dark matter scenarios, could generate a stochastic GW background with a maximum amplitude of h B G ≃ 10 - 2 4 and corresponding closure energy density of Ω G W 10 - 7 , in the frequency band ν o b s ≃ 30-470 Hz (assuming a maximum efficiency of generation of GWs, namely, eGw m a x = 7 X 10 - 4 ) for stars forming at redshifts z ≃ 30-10. We show that it will be possible in the future to detect this isotropic GW background by correlating the signals of a pair of advanced LIGO observatories (LIGO III) at a signal-to-noise ratio of ≃40. We discuss what astrophysical information could be obtained from a positive (or even a negative) detection of such a GW background generated in scenarios such as those studied here. One of them is the possibility of obtaining the initial and final redshifts of the emission period from the observed spectrum of GWs.

Collapse of primordial clouds — II. The role of dark matter

In this article we extend the study performed in our previous article on the collapse of primordial objects. We here analyze the behavior of the physical parameters for clouds ranging from 10 7 M⊙ to 10 15 M⊙. We studied the dynamical evolution of these clouds in two ways: purely baryonic clouds and clouds with non-baryonic dark matter included. We start the calculations at the beginning of the recombination era, following the evolution of the structure until the collapse (that we defined as the time when the density contrast of the baryonic matter is greater than 10 4 ). We analyze the behavior of the several physical parameters of the clouds (as, e.g., the density contrast and the velocities of the baryonic matter and the dark matter) as a function of time and radial position in the cloud. In this study all physical processes that are relevant to the dynamical evolution of the primordial clouds, as for example photon-drag (due to the cosmic background radiation), hydrogen molecular production, besides the expansion of the Universe, are included in the calculations. In particular we find that the clouds, with dark matter, collapse at higher redshift when we compare the results with the purely baryonic models. As a general result we find that the distribution of the nonbaryonic dark matter is more concentrated than the baryonic one. It is important to stress that we do not take into account the putative virialization of the non-baryonic dark matter, we just follow the time and spatial evolution of the cloud solving its hydrodynamical equations. We studied also the role of the cooling-heating processes in the purely baryonic clouds.

Probing a cosmological model with aΛ=Λ0+3βH2decaying vacuum

In this work we study the evolution of matter-density perturbations for an arbitrary

Collapse of primordial clouds - I

Lambda(t)

Comparing Single-Cycle and Multicycle Explosive Scenarios for the Formation of Voids

model, and specialize our analysis to the particular phenomenological law

Star formation rate density and the stochastic background of gravitational waves

Lambda = Lambda_0 + 3beta H^2

Connecting the Cosmic Star Formation Rate with the Local Star Formation

. We study the evolution of the cosmic star formation rate in this particular dark energy scenario and, by constraining the

Simulações de problemas em magneto-hidrodinâmica usando o código FLASH

beta

Simulating the interaction of a comet with the solar wind using a magnetohydrodynamic model

parameter using both the age of the universe and the cosmic star formation rate curve, we show that it leads to a reasonable physical model for