In this talk we derive closed general relativistic formulas for the mass M and the spin parameter a of a Kerr black hole in terms of observational data: the red- and blue-shifts of photons emitted by massive particles (stars or gas) geodesically orbiting around the black hole, and their respective orbital radius. It turns out that given a set of two (three) stars revolving around the Kerr...
Quark matter surface tension plays a key role in the understanding of neutron star (NS) interiors. However, despite its relevance for NS physics, the surface tension is still poorly known for quark matter. We focus on the thermodynamic conditions prevailing in NSs, hot lepton-rich protoneutron stars (PNSs), and binary NS mergers. We explore the role of temperature, baryon number density,...
In 2015 the first detection of gravitational waves was made, gravitational waves from the violent collision of two black holes. This collision sent waves through space-time as Einstein predicted. This detection was made possible by many advances in measurement technology, mainly vibration isolation for the detector optics; at 10 Hz, the motion of the laser interferometer detector mirrors is at...
Local galaxies are the endpoint of all cosmological evolution: to understand how galaxies evolve through cosmic time, we need a careful characterization of galaxy structures in the local universe. The Spitzer Survey of Stellar Structure in Galaxies (S4G) is one of the major legacy surveys of the post-cryogenic campaign of the Spitzer Space Telescope. With deep mid-infrared (3.6/4.5um) imaging...
During this talk I will present a novel proposal to explain cosmic inflation in the Universe with the following features: (i) its vacuum spectrum solely consists of a graviton and is ghost-free, (ii) it possesses well-behaved black hole solutions which coincide with those of Einsteinian cubic gravity, (iii) its cosmology is well-posed as an initial value problem and, most importantly, (iv) it...
In this talk I will present a systematic analysis of dark matter production during post-inflationary reheating. The damped oscillations of the inflation as it decays, the thermalization rate of its decay products, and the evolution of the temperature of the subsequently thermalized radiation determine the production rate of dark matter, and they are in turn dependent on the shape of the...
In this work, we calculate the decay rates of some resonances that can be considered as hybrid mesons. This study was carried out using the constituent gluon model. We specifically studied the resonances $\pi_1(1400)$ and $\pi_1(1600)$, since the lightest hybrid meson, with quantum numbers $J^{PC}$ = $1^{−+}$, is expected to be in this region of hadronic spectrum. The constituent gluon model...
Pulsars emit pulsed radiation in well-defined frequencies. In the canonical model, a pulsar is assumed to be a rotating, highly magnetized sphere made mostly of neutrons that has a magnetic dipole misaligned with respect to its rotation axis, which would be responsible for the emission of the observed pulses. The measurement of the pulse frequency and its first two derivatives allows the...
In today’s scenario, going beyond Einstein’s theory of gravity leads us to some more complete and modified theories of gravity. One of them is the f(R,T) gravity in which R is the Ricci scalar, and T is the trace of energy-momentum tensor. A well-motivated f(R,T) gravity model, f(R,T) = R + αRT where α is the model parameter is considered here. In this work, we studied the strong energy...
This work starts from a toy model for inflation in a class of modified theories of gravity in the metric formalism. Instead of the standard procedure -- assuming a non-linear Lagrangian f(R) in the Jordan frame -- we start from a simple φ$^2$ potential in the Einstein frame and investigate the corresponding f(R) in the former picture. The addition of an ad-hoc Cosmological Constant in the...
Cyg X-3 is the famous binary system containing a black hole. It is actively studied through the wide range of electromagnetic spectrum from radio band up to ultrahigh energies. Cyg X-3 has long been considered as an object for very high energy gamma-ray observations. We present the results of more than 20-year-long studies of Cyg X-3 in the range of 800 GeV–100 TeV with the SHALON telescope....
The hypothesis that one or more biodiversity drops in the Phanerozoic eon, evident in the geological record, might have been caused by the most powerful kind of stellar explosion so far known (Gamma Ray Bursts) has been discussed in several works. These stellar explosions could have left an imprint in the biological evolution on Earth and in other habitable planets. In this work we calculate...
The experimental data obtained with Pamela, Fermi, AMS-02, spectrometers cannot be explained using the diffusive models of propagation of cosmic-rays accelerated at the supernova shocks and require the existence of nearby sources of cosmic rays at the distances less than one kpc. These sources could explain the growth of the ratio of galactic positrons to electrons with an increase of their...
We will present the detection of eight candidate extragalactic fast X-ray transients (+ XRT 170831 which was identified previously by Lin et al. 2019) from a parent sample of 214,701 sources in the Chandra Source Catalog Release 2.0 above $|b|{>}10^{\circ}$ (160.96 Ms over 592.4 deg$^{2}$). Our candidates have peak fluxes between 3.5$\times$10$^{-15}$ to 1.1$\times$10$^{-13}$ erg cm$^{-2}$...
We present X-ray spectra spanning 18 years of evolution for SN1996cr, one of the five nearest (~4 Mpc) SNe detected in the modern era. HETG observations allow us to resolve spectrally the velocity profiles of Ne, Mg, Si, S, and Fe emission lines and monitor their evolution as tracers of the ejecta-circumstellar medium (CSM) interaction. To explain the diversity of X-ray line profiles, we...
