arXiv subjects

Slawomir Stachniewicz

Publications and source records attributed to Slawomir Stachniewicz.

5 recordsLinked to original sources

arXiv2006

The Influence of External UV Radiation Field on Primordial Gas Clouds: Formulation of the Problem

Our goal is to study the effects of the UV radiation from the first stars, quasars and decays of the hypothetical Super Heavy Dark Matter (SHDM) particles on the formation of primordial bound objects in the Universe. We trace the evolution of a spherically symmetric density perturbation in the Lambda Cold Dark Matter ($Λ$CDM) and MOND models, solving the frequency-dependent radiative transfer equation, non-equilibrium chemistry, and one-dimensional gas hydrodynamics. We concentrate on the destruction and formation processes of the H$_2$ molecule, which is the main coolant in the primordial objects.

astro-ph↗

arXiv2006

Collapse of the Primordial Gas Clouds in the Presence of UV Radiation Field

Our goal is to study the effects of the UV radiation from the first stars, quasars and hypothetical Super Heavy Dark Matter (SHDM) particle decays on the formation of primordial bound objects in the Universe. We trace the evolution of a spherically symmetric density perturbation in the Lambda Cold Dark Matter and MOND model, solving the frequency-dependent radiative transfer equation, non-equilibrium chemistry, and one-dimensional gas hydrodynamics. We concentrate on the destruction and formation processes of the $H_{2}$ molecule, which is the main coolant in the primordial objects.

astro-ph↗

arXiv2004

The end of the Dark Ages in MOND

We study the evolution of a spherically symmetric density perturbation in the Modified Newtonian Dynamics (MOND) model applied to the net acceleration over Hubble flow. The background cosmological model is a $Λ$-dominated, low-$Ω_b$ Friedmann model with no Cold Dark Matter. We include thermal processes and non-equilibrium chemical evolution of the collapsing gas. We find that under these assumptions the first low-mass objects ($M \le 3\times 10^4 M_{\odot}$) may collapse already for $z\sim 30$, which is in quite good agreement with the recent WMAP results. A lower value of $a_0$ would lead to much slower collapse of such objects.

astro-ph↗

arXiv2002

The First Compact Objects in the $Λ$-dominated Universe

We calculate the evolution of a low-mass ($M \le 10^5 M_{\odot}$) spherically symmetric density perturbation in the $Ω_b h^2=0.02$, $Ω_M =0.35$, $Ω_Λ=0.65$, $h=0.72$ Universe. The results are compared with the ones that assume no cosmological constant and the flat, dark matter dominated Universe. We include thermal processes and non-equilibrium chemical evolution of the collapsing gas. We find that direct formation of bound objects with such masses by $z=8$ is unlikely so in fact they may form only through fragmentation of greater objects. This is in stark contrast to the $Ω=1$ pure CDM cosmology, where low-mass objects form abundantly at redshits $z>10$.

astro-ph↗

arXiv2001

The first compact objects in the MOND model

We trace the evolution of a spherically symmetric density perturbation in the MOdified Newtonian Dynamics (MOND) model. The background cosmological model is a $Λ$-dominated, low-$Ω_b$ Friedmann model with no Cold Dark Matter. We include thermal processes and non-equilibrium chemical evolution of the collapsing gas. We find that the first density perturbations which collapse to form luminous objects have mass $\sim 10^5 M_{\odot}$. The time of the final collapse of these objects depends mainly on the value of the MOND acceleration $a_0$ and also on the baryon density $Ω_b$. For the "standard" value $a_0=1.2\times 10^{-8}$ cm/s$^2$ the collapse starts at redshift $z \sim 160$ for $Ω_b=0.05$ and $z \sim 110$ for $Ω_b=0.02$.

astro-ph↗