Related papers: The Case for Astrons
We use the constraints arising from primordial nucleosynthesis to bound a putative electric charge density $|e|n_q$ of the universe. We find $|n_q/n_\gamma| \lesssim 10^{-43}$, four orders of magnitude more stringent than previous limits.…
(Abridge): We present a spectroscopic study of the stellar populations of Low Luminosity AGN (LLAGN). Our main goal is to determine whether the stars who live in the innermost (100 pc-scale) regions of these galaxies are in some way related…
The nature of dark matter (DM) remains unknown despite very precise knowledge of its abundance in the universe. An alternative to new elementary particles postulates DM as made of macroscopic compact halo objects (MACHO) such as black holes…
Quartic gravity theory is considered with the Einstein-Hilbert Lagrangean $R+aR^{2}+bR_{\mu \nu}R^{\mu \nu},$ $R_{\mu \nu}$ being Ricci\'s tensor and R the curvature scalar. The parameters $a$ and $b$ are taken of order 1 km$^{2}.$…
Cosmological inflation is not the only early universe scenario consistent with current observational data. I will discuss the criteria for a successful early universe cosmology, compare a couple of the proposed scenarios (inflation,…
Old neutron stars (ONSs) which have radiated away their internal and rotational energy may still shine if accreting the interstellar medium. Despite their large number, only two promising candidates have been detected so far and rather…
We present the stellar population content of early-type galaxies from the Atlas3D survey. Using spectra integrated within apertures covering up to one effective radius, we apply two methods: one based on measuring line-strength indices and…
The mass function (MF) of isolated objects measured by microlensing consists of both a stellar and a planetary component. We compare the microlensing MFs of Gould et al (2022) and Sumi et al (2023) to other measurements of the MF. The…
Unveiling the nature of progenitors is crucial for understanding the origin and the mechanism of core-collapse and thermonuclear supernovae (SNe). While several methods have been developed to derive stellar properties so far, many questions…
In order to facilitate the identification of possible new physics signatures in neutrino telescopes, such as neutrinos from the annihilation of neutralinos or decaying relics, it is essential to gain full control over the astrophysical…
We present a theoretical model for primordial star formation. First we describe the structure of the initial gas cores as virialized, quasi-hydrostatic objects in accord with recent high resolution numerical studies. The accretion rate can…
A population of unidentified gamma-ray sources is forming a structure resembling a halo around the Galactic center. These sources are highly variable, and hence they should be associated with compact objects. Microquasars are objects…
Within the context of hot big-bang cosmology, a cosmic background of presently low energy neutrinos is predicted to exist in concert with the photons of the cosmic background radiation. The number density of the cosmological neutrinos is of…
The existence of neutron stars with masses of $\sim 2\,M_{\odot}$ requires a stiff equation of state at high densities. On the other hand, the necessary appearance also at high densities of new degrees of freedom, such as hyperons and…
Beyond the linear regime, the power spectrum and higher order moments of the matter field no longer capture all cosmological information encoded in density fluctuations. While non-linear transforms have been proposed to extract this…
We studied the environment of a sample of galaxies in which the presence of polar rings or the presence of gas- and stars- counterrotation is observed. These galaxies are believed to have accreted this material, now in peculiar motion, from…
Using the cosmological constants derived from WMAP, the standard big bang nucleosynthesis (SBBN) predicts the light elements primordial abundances for 4He, 3He, D, 6Li and 7Li. These predictions are in satisfactory agreement with the…
A widely accepted viewpoint is to consider candidates for cosmological dark matter as neutral and weakly interacting particles, as well as to consider only light elements in the pregalactic chemical composition. It is shown that stable…
We present radio observations at 1.5 GHz of 32 local objects selected to reproduce the physical properties of $z\sim5$ star-forming galaxies. We also report non-detections of five such sources in the sub-millimetre. We find a radio-derived…
Abundances for alpha-elements and Fe in about 150 field subdwarfs and early subgiants with accurate parallaxes and kinematic data are used to discuss the run of abundance ratios in metal-poor stars in the solar neighborhood. Based on…