arXiv subjects

T. Kenneth Fowler

Publications and source records attributed to T. Kenneth Fowler.

3 recordsLinked to original sources

arXiv2024

Accreting Primordial Black Holes: Dark Matter Constituents

We show scenarios in which primordial black hole accretion under the magnetorotational instability (MRI) uniquely relates the density of the early Universe to the abundance of present day dark matter. We demonstrate via long duration general relativistic magnetohydrodynamic (GRMHD) simulations that MRI-dominated accretion at least hundreds of gravitational radii from black holes can occur under conditions expected in the Positronium Era. We thereby identify that the positronium plasma that existed 0.01 s to 14 s into the Big Bang can serve as the primary source of mass that augmented primordial black hole seeds to 10^16-10^17g black holes contributing to dark matter today. This population of black holes, in turn, radiates in a manner consistent with the observed gamma ray background. At a time of uncertainty about the role of new kinds of particles, the better understood primordial black hole MRI accretion process may be the best way to pin down how much dark matter mass lies behind horizons versus new dark sector particles.

astro-ph.HE↗

arXiv2023

Accreting Primordial Black Holes as Dark Matter Constituents

We show how magnetic accretion of positronium (electron-positron) plasma by primordial black holes might significantly contribute to the mass of dark matter in the present Universe. Assuming that background gamma radiation is primordial black hole Hawking radiation rules out Bondi accretion, while magnetic accretion known from studies of active galactic nuclei could explain the abundance of dark matter. Various accretion scenarios are discussed.

astro-ph.HE↗

arXiv2019

Hyper-Resistive Model of Ultra High Energy Cosmic Ray Acceleration by Magnetically Collimated Jets Created by Active Galactic Nuclei

This is the fourth in a series of companion papers showing that, when an efficient dynamo can be maintained by accretion disks around supermassive black holes in Active Galactic Nuclei (AGNs), it will lead to the formation of a powerful, magnetically-collimated helix that could explain both the observed jet/radiolobe structures on very large scales and ultimately the enormous power inferred from the observed ultra high energy cosmic rays (UHECRs) with energies > 10^19 eV. Many timescales are involved in this process. Our hyper-resistive magnetohydrodynamic (MHD) model provides a bridge between General Relativistic MHD simulations of dynamo formation, on the short accretion timescale, and observational evidence of magnetic collimation of large-scale jets on astrophysical timescales. Given the final magnetic structure, we apply hyper-resistive kinetic theory to show how instability causes slowly-evolving magnetically-collimated jets to become the most powerful relativistic accelerators in the Universe. The model yields nine observables in reasonable agreement with observations: the jet length, radiolobe radius and apparent opening angle as observed by synchrotron radiation; the synchrotron total power, synchrotron wavelengths and maximum electron energy (TeVs); and the maximum UHECR energy, the cosmic ray energy spectrum and the cosmic ray intensity on Earth.

astro-ph.HE↗