arXiv subjects

Félix Llorente de Andrés

Publications and source records attributed to Félix Llorente de Andrés.

4 recordsLinked to original sources

arXiv2024

Some Old Globular Clusters (and Stars) Inferring That the Universe Is Older Than Commonly Accepted

The James Webb Space Telescope (JWST) has made startling discoveries regarding the early universe. It has revealed galaxies as soon as 300 million years after the Big Bang, challenging current galaxy formation models. Additionally, it has identified massive, bright galaxies in the young universe, contradicting the standard ΛCDM model's age estimate of 13.8 Gyr. This prompts a reevaluation of galaxy formation and cosmological models. There is a strong tension between JWST high-redshift galaxy observations and Planck Cosmic Microwave Background (CMB) satellite measurements. Even alternative cosmological models, including those incorporating dark matter baryon interaction, f(R) gravity, and dynamical dark have failed to resolve this tension. One possible solution is that the Universe's age exceeds predictions by the ΛCDM model. The study challenges this by introducing a method based on blue straggler stars (BSs) within GCs, comparing ages with other models. The ages obtained are compared with those of different models to certify that they are equally valid. These values are comparable within the error ranges except for the clusters: NGC104, NGC 5634, IC 4499, NGC 6273 and NGC 4833, finding their respective ages to be between 14.7 and 21.6 Gyr, surpassing the commonly accepted age of the Universe. These results inferred an age for the Universe of around 26 Gyr, close to 26.7 Gyr. This value aligns with that suggested by the cosmological model named Covarying Coupling Constants + TL (CCC+TL). Such a value is consistent with early universe observations from the James Webb Space Telescope (JWST). The results of the present paper reinforce the advocating for a critical review of models encompassing dark mass, dark energy, and the dynamics of the Universe, particularly in explaining the presence of primitive massive galaxies, very old GCs, and very old and poor metallic stars.

astro-ph.GA↗

arXiv2023

Could the number of blue straggler stars help to determine the age of their parent globular cluster?

A recent study shows, from an empirical deduction, that the number and the presence of the blue straggler stars (BSS) in an open cluster follow a function whose components are the ratio between age and the relaxation time, $\it f$, and a factor, $\varpi$ , which is an indicator of stellar collisions plus primordial binaries. The relation among the number of blue straggler stars, the factor $\it f$, and the factor $\varpi$ of each globular cluster allows for deriving the age of the respective globular clusters. This method has been applied individually over 56 globular clusters containing BSS. The values derived for the cluster ages from our methodology do not differ from those derived from other methods. A special case is cluster NGC 104 whose age exceeds 13.8 Gyr (its age is between 19.04 and 20.30 Gyr), which would have a very exotic explanation: the existence of an intermediate black hole in the center of the cluster. That black hole main-sequence star (BH-MS) binaries with an initial orbital period less than the bifurcation period can evolve into ultra-compact X-ray binaries (UCXBs) that can be detected by LISA. On the other hand, if that age were true, it would call into question the expansion velocity for a flat Universe. This would call into question the case for dark energy dominated Universe.

astro-ph.SR↗

arXiv2022

Open clusters: time-scales, core collapse and blue stragglers

We developed a mathematical model to derive time scales and the presence of BS stars. The model is based on the variation of mass through a circle into the cluster defined by a radius, and at a time; this mass cross is translated into a differential equation that it can be integrated for a given radius (r) and a determined time (t). From this equation we can derive the different time scales that allows us to reach conclusions like: clusters not containing blue strugglers (BS) stars disappear younger than those clusters containing BS. In clusters containing BS stars, the volume which takes up half of the cluster mass is bigger than the one corresponding to clusters without BS stars but the time to catch it up is shorter. We also studied, by means of this equation, the core collapse of stars of the cluster and the region where this concentration is stopped/retained; this region is identified by means of the relation $c/ch$, being $c=\log(rt/rc)$ and $ch=\log(rc/rh)$. Where rt and rc are the tidal and the core radius respectively, and rh is the radius where half of the cluster mass is concentrated. The model also drove us to the conclusion that the number of the blue straggler stars in a cluster follows a distribution function whose components are the ratio between relaxation time and the age, labelled as $\it f$, and a factor, named $\varpi$, which is an indicator of the origin of the BS; $\varpi$ increases as the number of BS increase but it is limited to$\sim$5.0. The mentioned distribution function is expressed as $\it NBS$ $\sim$ $\it f^3$($\frac{1}{e^{\frac{f}{\varpi}}-1}$). The validity of this function was carried out by means of matching the number of observed blue straggler (BS) stars to the number of predicted ones in the available sample of OC.

astro-ph.SR↗

arXiv2021

The bi-modal $^7$Li distribution of the Milky Way's thin-disk dwarf stars: The role of Galactic-scale events and stellar evolution

The lithium abundance, A(Li), in stellar atmospheres suffers from various enhancement and depletion processes during the star's lifetime. While several studies have demonstrated that these processes are linked to the physics of stellar formation and evolution, the role that Galactic-scale events play in the galactic A(Li) evolution is not yet well understood. We aim to demonstrate that the observed A(Li) bi-modal distribution, in particular in the FGK-dwarf population, is not a statistical artefact and that the two populations connect through a region with a low number of stars. We also want to investigate the role that Galactic-scale events play in shaping the A(Li) distribution of stars in the thin disk. We use statistical techniques along with a Galactic chemical evolution model for A(Li) that includes most of the well-known $^7$Li production and depletion channels. We confirm that the FGK main-sequence stars belonging to the Milky Way's thin disk present a bi-modal A(Li) distribution. We demonstrate that this bi-modality can be generated by a particular Milky Way star formation history profile combined with the stellar evolution's $^7$Li depletion mechanisms. We show that A(Li) evolution can be used as an additional proxy for the star formation history of our Galaxy.

astro-ph.GA↗