arXiv subjects

Mikalai Prakapenia

Publications and source records attributed to Mikalai Prakapenia.

7 recordsLinked to original sources

arXiv2026

Emission and cooling of a newborn quark star

It has long been believed that newborn quark stars are inefficient emitters because the quark plasma frequency is so high that it suppresses electromagnetic radiation across the entire spectrum up to energies of several tens of MeV. Here, we show that significant electromagnetic emission can instead originate from the electrosphere of a quark star, where the plasma frequency is much lower, approximately 40 keV. As a result, the cooling of a newborn quark star is expected to proceed through two distinct observational epochs. During the first epoch, blackbody radiation is emitted from the photosphere of an optically thick relativistic wind generated near the electrosphere. Over the course of a few days following the star's formation, the photospheric temperature decreases from several MeV to about 22 keV. During the second epoch, the blackbody spectrum evolves into a narrow feature centered around 40 keV, and the emission gradually fades. This spectral evolution provides a characteristic signature of the electrosphere surrounding compact astrophysical objects and may be detectable with current or future X-ray observatories.

astro-ph.HE↗

arXiv2026

Pair luminosity and cooling of newborn strange star: Color-flavor-locked and two-flavor color superconducting quarks

Following the previous wor k[1] here we consider early thermal evolution of hot strange stars made of color superconducting quarks in two different pairing states: two-flavor color superconductor (2SC) and color-flavor-locked (CFL) phases, taking into account cooling by neutrinos and electron-positron pair creation due to the Schwinger process. We show that Schwinger luminosity in the electrosphere is a universal function of temperature, independent of quark matter phase for quark chemical potential $μ_q>280$ MeV. The surface of a strange star in all the cases cools faster than its interior. This leads to a fast decrease of pair luminosity with time, so that it does not exceed $10^{46}$ erg/s at 1 second after strange star formation. Neutrino luminosity dominates over pair luminosity in all the cases except for the CFL phase with a large gap parameter $Δ>60$ MeV, where there is a strong suppression of neutrino emission. The total energy emitted in electron-positron pairs is always smaller than the energy emitted in neutrinos, but they become comparable for the large gap parameter.

astro-ph.HE↗

arXiv2026

Pair luminosity and cooling of newborn strange star: unpaired quarks

It was shown that pair luminosity of the newborn strange star with temperature of $10^{11}$ K may be as high as $L_\pm\simeq 10^{52}$ erg/s. The question remains: can a strange star maintain such a high surface temperature for a long time? To answer this question we studied thermal evolution of newborn strange star made of unpaired quarks taking into account its thermal conductivity and neutrino emission by the URCA processes $d\rightarrow u + e + \barν_e$ and $u+e\rightarrow d+ν_e$. Our results show that extremely high luminosity due to the Schwinger process and insufficient thermal conductivity of quarks leads to development of steep temperature gradient at the surface of strange star. As a result, the temperature at the surface and hence its luminosity decreases, reaching $10^{43}$ erg/s already at $10^2$ seconds. This result holds even in the presence of neutrinosphere.

astro-ph.HE↗

arXiv2025

Pair creation from radial electromagnetic perturbation of a compact astrophysical object

Recently Usov's mechanism of pair creation on the surface of compact astrophysical objects has been revisited [1] with a conclusion that the pair creation rate was previously underestimated in the literature by nearly two orders of magnitude. Here we consider an alternative hypothesis of pair creation due to a perturbation of the surface of a compact object. Radial perturbation is induced in hydrodynamic velocity resulting in a microscopic displacement of the negatively charged component with respect to the positively charged one. The result depends on the ratio between the spatial scale of the perturbation $λ$ and the mean free path $l$. When $λ\sim l$ the perturbation energy is converted into a burst of electron-positron pairs which are created in collisionless plasma oscillations at the surface; after energy excess is dissipated electrosphere returns to its electrostatic configuration. When instead $λ\gg l$, the perturbation is thermalized, its energy is transformed into heat, and pairs are created continuously by the heated electrosphere. We discuss the relevant astrophysical scenarios.

astro-ph.HE↗

arXiv2024

On the single versus the repetitive Penrose process in a Kerr black hole

Extracting the rotational energy from a Kerr black hole (BH) is one of the crucial topics in relativistic astrophysics. Here, we give special attention to the Penrose ballistic process based on the fission of a massive particle $μ_0$ into two particles $μ_1$ and $μ_2$, occurring in the ergosphere of a Kerr BH. Bardeen et al. indicated that for the process to occur, some additional "hydrodynamical forces or superstrong radiation reactions" were needed. Wald and Chandrasekhar further expanded this idea. This animosity convinced T. Piran and collaborators to move from a simple three-body system characterizing the original Penrose process to a many-body system. This many-body approach was further largely expanded by others, some questionable in their validity. Here, we return to the simplest original Penrose process and show that the solution of the equations of motion, imposing the turning point condition on their trajectories, leads to the rotational energy extraction from the BH expected by Penrose. The efficiency of energy extraction by a single process is quantified for three different single decay processes occurring respectively at $r=1.2 M$, $r=1.5 M$, and $r=1.9 M$. An interesting repetitive model has been proposed by Misner, Thorne \& Wheeler (hereafter MTW73). Indeed, it would appear that a repetitive sequence of $246$ decays of the above injection process at $r=1.2 M$ and the corresponding ones at $r=1.5 M$ and $r=1.9 M$ could extract $100\%$ of the rotational energy of the BH, so violating energy conservation. The accompanying paper, accounting for the existence of the BH irreducible mass, introduces a non-linear approach that avoids violating energy conservation and leads to a new energy extraction process.

gr-qc↗

arXiv2023

Pair creation in hot electrosphere of compact astrophysical objects

The mechanism of pair creation in electrosphere of compact astrophysical objects such as quark stars or neutron stars is revisited, paying attention to evaporation of electrons and acceleration of electrons and positrons, previously not addressed in the literature. We perform a series of numerical simulations using the Vlasov-Maxwell equations. The rate of pair creation strongly depends on electric field strength in the electrosphere. Despite Pauli blocking is explicitly taken into account, we find no exponential suppression of the pair creation rate at low temperatures. The luminosity in pairs increases with temperature and it may reach up to $L_\pm\sim 10^{52}$ erg/s, much larger than previously assumed.

astro-ph.HE↗

arXiv2023

Pauli blocking effects on pair creation in strong electric field

The process of electron-positron pair creation and oscillation in uniform electric field is studied, taking into account Pauli exclusion principle. Generally, we find that pair creation is suppressed, hence coherent oscillations occur on longer time scales. Considering pair creation in already existing electron-positron plasma we find that the dynamics depends on pair distribution function. We considered Fermi-Dirac distribution of pairs and found that for small temperatures pair creation is suppressed, while for small chemical potentials it increases: heating leads to enhancement of pair creation.

physics.plasm-ph↗