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Seminarium środowe



20.03.2024

"Binary coalescences as sources of ultrahigh-energy cosmic rays"

Jonas Pereira (Núcleo de Astrofísica e Cosmologia & Departamento de Física, Universidade Federal do Espírito Santo, Vitória, Brasil and CAMK, W)

Binary coalescences are known sources of gravitational waves (GWs) and they encompass combinations of black holes (BHs) and neutron stars (NSs). I’ll show that when BHs are embedded in magnetic fields (B’s) larger than approximately e10 G, charged particles colliding around their event horizons can easily have ultrahigh energies (≳ e18 eV) and become more likely to escape. Such B-embedding and high-energy particles can take place in BH-NS binaries, or even in BH-BH binaries with one of the BHs being charged (with charge-to-mass ratios as small as e-5, which do not change GW waveforms) and having a residual accretion disk. The number of collisions leading to ultrahigh energy particles is estimated to range from a few up to millions before the merger of binary compact systems. Thus, binary coalescences may also be efficient sources of ultrahigh energy cosmic rays (UHECRs) and constraints to NS/BH parameters would be possible if UHECRs are detected along with GWs.

The presentation will be based on recent PRL work: Binary Coalescences as Sources of Ultrahigh-Energy Cosmic Rays Jonas P. Pereira, Carlos H. Coimbra-Araújo, Rita C. dos Anjos, and Jaziel G. Coelho Phys. Rev. Lett. 132, 091401 – Published 27 February 2024


27.03.2024

"Thermal effects in nuclear matter and neutron stars"

Lucas Tonetto (Dipartimento di Fisica, “Sapienza” University of Rome, Italy)

In different astrophysical systems involving neutron stars, such as mergers or newly born stars, a reliable model of a finite-temperature equation of state is needed. Temperature has implications in equilibrium and dynamical phenomena, therefore a fully consistent framework should be able to take into account thermal effects in single-nucleon properties alongside yielding accurate results for average thermodynamic quantities. In this talk, I present the results of employing a recently developed effective interaction based on the Correlated Basis Functions theory, being able to account for nuclear correlations and two- and three-nucleon potentials. After discussing the properties of its generalisation to nonzero temperature, we apply it in the calculation of the neutrino mean free path and emissivity. In the latter, we study how in-medium effects alter the results by using effective weak transition operators.


03.04.2024

"Magnetic flux saturation mechanism at accreting black holes"

Krzysztof Nalewajko (CAMK, Warsaw)

Black holes (BH) acquire relativistic magnetospheres by accreting magnetized gas. Once they collect significant magnetic flux across the horizon, aided by the spin they can drive powerful relativistic jets by the Blandford-Znajek mechanism. Large enough BH magnetic flux backreacts on the accretion flow, which has been described in terms of arresting or choking. Magnetic flux eruptions have been identified as the mechanism of BH magnetic flux saturation. These eruptions can potentially dissipate a large fraction of magnetic energy in the BH magnetosphere by means of relativistic magnetic reconnection, accelerating particles and producing flares of non-thermal radiation. We analyze the results of 3D general-relativistic ideal magnetohydrodynamic (GRMHD) numerical simulations of accretion flows onto magnetically saturated Kerr BHs, focusing on the initiation of magnetic flux eruptions.