Production and Persistence of Extreme Two-temperature Plasmas in Radiative Relativistic Turbulence

• Published in: The Astrophysical journal Vol. 908; no. 1; pp. 71 - 76
• Main Authors: Zhdankin, Vladimir, Uzdensky, Dmitri A., Kunz, Matthew W.
• Format: Journal Article
• Language: English
• Published: Philadelphia The American Astronomical Society 01.02.2021; IOP Publishing
• Subjects: 70 PLASMA PHYSICS AND FUSION TECHNOLOGY; Accretion; Astronomical models; Astrophysics; Computational fluid dynamics; Cooling; Cosmic rays; Deposition; Electron energy; High energy astronomy; High energy astrophysics; High energy electrons; Ions; Luminosity; Non-thermal radiation sources; Particle in cell technique; Plasma astrophysics; Plasma turbulence; Radiation; Radiation effects; Radiative cooling; Relativistic effects; Relativistic jets; Relativistic particles; Relativistic plasmas; Simulation; Temperature ratio; Thermal coupling
• DOI: 10.3847/1538-4357/abcf31
• ISSN: 0004-637X; 1538-4357

Turbulence is a predominant process for energizing electrons and ions in collisionless astrophysical plasmas, and thus is responsible for shaping their radiative signatures (luminosity, spectra, and variability). To better understand the kinetic properties of a collisionless radiative plasma subject to externally driven turbulence, we investigate particle-in-cell simulations of relativistic plasma turbulence with external inverse Compton cooling acting on the electrons. We find that ions continuously heat up while electrons gradually cool down (due to the net effect of radiation), and hence the ion-to-electron temperature ratio Ti/Te grows in time. We show that Ti/Te is limited only by the size and duration of the simulations (reaching ), indicating that there are no efficient collisionless mechanisms of electron-ion thermal coupling. This result has implications for models of radiatively inefficient accretion flows, such as observed in the Galactic center and in M87, for which so-called two-temperature plasmas with have been invoked to explain their low luminosity. Additionally, we find that electrons acquire a quasi-thermal distribution (dictated by the competition of turbulent particle energization and radiative cooling), while ions undergo efficient nonthermal acceleration (acquiring a harder distribution than in equivalent nonradiative simulations). There is a modest nonthermal population of high-energy electrons that are beamed intermittently in space, time, and direction; these beamed electrons may explain rapid flares in certain high-energy astrophysical systems (e.g., in the Galactic center). These numerical results demonstrate that extreme two-temperature plasmas can be produced and maintained by relativistic radiative turbulence.