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A special issue of Galaxies (ISSN 2075-4434).

Deadline for manuscript submissions: closed (7 November 2018) | Viewed by 55387

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Prof. Dr. Athina Meli

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Guest Editor

College of Science and Technology, North Carolina A&T State University, Greensboro, NC 27411, USA
Interests: cosmic-rays; high-energy astrophysics; relativistic jets; extragalactic astronomy
Special Issues, Collections and Topics in MDPI journals

Dr. Yosuke Mizuno

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Guest Editor

Institute for Theoretical Physics, Goethe University Frankfurt, 60323 Frankfurt, Germany
Interests: high-energy astrophysics; plasma astrophysics; relativistic astrophysics; black hole; relativistic jets; active galactic nuclei; gamma-ray bursts; pulsar wind nebula; accretion disks; shock; instability; turbulence; GRMHD & RMHD simulations

Dr. Jose L. Gómez

E-Mail Website
Guest Editor

Instituto de Astrofísica de Andalucía–CSIC, Glorieta de la astronomía s/n, Granada 18008, Spain
Interests: high energy astrophysics; active galactic nuclei; relativistic jets; blazars; RMHD simulations; very long baseline interferometry; radio-astronomy; multi-waveband observations

Special Issue Information

Dear Colleagues,

During the last few decades, plasma science has witnessed a great growth in laboratory studies, simulations and in space. Plasma is the most common phase of ordinary matter in the universe. It is a state in which ionized matter (even as low as 1%) becomes highly electrically conductive, and, as such, long range electric and magnetic fields dominate its behavior. Cosmic plasmas are mostly associated with stars, supernovae, pulsars and neutron stars, quasars and active galaxies, mostly at their central black-holes (i.e., jets, accretion disks). Cosmic plasma phenomena are studied with different methods such as laboratory experiments, astrophysical observations and computational approaches (i.e., MHD or Particle-In-Cell simulations, etc.), exhibiting a multitude of complex magnetohydrodynamic behaviors, acceleration, radiation, turbulence and various instability phenomena. This Special Issue will aim to address the growing need of the plasma science principles in astrophysics and to present our current understanding of the physics of astrophysical plasmas, their electromagnetic behaviors and properties, such as shocks, waves, turbulence, instabilities, collimation, acceleration and radiation, microscopically and macroscopically. Therefore, our purpose will be to provide an up-to-date overview of the cosmic plasma studies widely through astrophysical observations, laboratory experiments, simulation techniques, and theoretical models.

References:

Jorstad et al. 2017: http://adsabs.harvard.edu/abs/2017ApJ...846...98J
Lister et al. 2009: http://adsabs.harvard.edu/abs/2009AJ....137.3718L
Ghisellini et al. 2010: http://adsabs.harvard.edu/abs/2010MNRAS.402..497G
Doeleman et al. 2008: http://adsabs.harvard.edu/abs/2008Natur.455...78D
Falcke et al. 2004: http://adsabs.harvard.edu/abs/2004A%26A...414..895F
Font 2008: http://adsabs.harvard.edu/abs/2008LRR....11....7F
Sironi et al. 2015: http://adsabs.harvard.edu/abs/2015SSRv..191..519S
McKinney & Blandford 2012: http://adsabs.harvard.edu/abs/2009MNRAS.394L.126M
Kronberg, P. P., Lovelace, R. V. E., Lapenta, G., Colgate, S. A., 2011: http://adsabs.harvard.edu/abs/2011ApJ...741L..15K
Christodoulou, D. M., Gabuzda, D. C., Knuettel, S., Contopoulos, I., Kazanas, D., Coughlan, C. P., 2016: http://adsabs.harvard.edu/abs/2016A%26A...591A..61C

Dr. Athina Meli
Dr. Yosuke Mizuno
Dr. Jose L. Gómez
Guest Editors

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Published Papers (11 papers)

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Research

Jump to: Review

18 pages, 2880 KiB

Open AccessArticle

Relativistic Aspects of Accreting Supermassive Black Hole Binaries in Their Natural Habitat: A Review

by Roman Gold

Galaxies 2019, 7(2), 63; https://doi.org/10.3390/galaxies7020063 - 31 May 2019

Cited by 19 | Viewed by 4138

Abstract

In this review a summary is given on recent theoretical work, on understanding accreting supermassive black hole binaries in the gravitational wave (GW)-driven regime. A particular focus is given to theoretical predictions of properties of disks and jets in these systems during the gravitational wave driven phase. Since a previous review by Schnittman 2013, which focussed on Newtonian aspects of the problem, various relativistic aspects have been studied. In this review we provide an update on these relativistic aspects. Further, a perspective is given on recent observational developments that have seen a surge in the number of proposed supermassive black hole binary candidates. The prospect of bringing theoretical and observational efforts closer together makes this an exciting field of research for years to come. Full article

(This article belongs to the Special Issue Cosmic Plasmas and Electromagnetic Phenomena)

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30 pages, 1085 KiB

Open AccessArticle

Plasmas in Gamma-Ray Bursts: Particle Acceleration, Magnetic Fields, Radiative Processes and Environments

by Asaf Pe’er

Galaxies 2019, 7(1), 33; https://doi.org/10.3390/galaxies7010033 - 15 Feb 2019

Cited by 2 | Viewed by 5096

Abstract

Being the most extreme explosions in the universe, gamma-ray bursts (GRBs) provide a unique laboratory to study various plasma physics phenomena. The complex light curve and broad-band, non-thermal spectra indicate a very complicated system on the one hand, but, on the other hand, provide a wealth of information to study it. In this chapter, I focus on recent progress in some of the key unsolved physical problems. These include: (1) particle acceleration and magnetic field generation in shock waves; (2) possible role of strong magnetic fields in accelerating the plasmas, and accelerating particles via the magnetic reconnection process; (3) various radiative processes that shape the observed light curve and spectra, both during the prompt and the afterglow phases, and finally (4) GRB environments and their possible observational signature. Full article

(This article belongs to the Special Issue Cosmic Plasmas and Electromagnetic Phenomena)

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20 pages, 13460 KiB

Open AccessEditor’s ChoiceArticle

Relativistic Jet Simulations of the Weibel Instability in the Slab Model to Cylindrical Jets with Helical Magnetic Fields

by Ken-Ichi Nishikawa, Yosuke Mizuno, Jose L. Gómez, Ioana Duţan, Athina Meli, Jacek Niemiec, Oleh Kobzar, Martin Pohl, Helene Sol, Nicholas MacDonald and Dieter H. Hartmann

Galaxies 2019, 7(1), 29; https://doi.org/10.3390/galaxies7010029 - 30 Jan 2019

Cited by 11 | Viewed by 5348

Abstract

The particle-in-cell (PIC) method was developed to investigate microscopic phenomena, and with the advances in computing power, newly developed codes have been used for several fields, such as astrophysical, magnetospheric, and solar plasmas. PIC applications have grown extensively, with large computing powers available on supercomputers such as Pleiades and Blue Waters in the US. For astrophysical plasma research, PIC methods have been utilized for several topics, such as reconnection, pulsar dynamics, non-relativistic shocks, relativistic shocks, and relativistic jets. PIC simulations of relativistic jets have been reviewed with emphasis placed on the physics involved in the simulations. This review summarizes PIC simulations, starting with the Weibel instability in slab models of jets, and then focuses on global jet evolution in helical magnetic field geometry. In particular, we address kinetic Kelvin-Helmholtz instabilities and mushroom instabilities. Full article

(This article belongs to the Special Issue Cosmic Plasmas and Electromagnetic Phenomena)

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37 pages, 12791 KiB

Open AccessEditor’s ChoiceArticle

Progress in Multi-Wavelength and Multi-Messenger Observations of Blazars and Theoretical Challenges

by Markus Böttcher

Galaxies 2019, 7(1), 20; https://doi.org/10.3390/galaxies7010020 - 18 Jan 2019

Cited by 108 | Viewed by 7230

Abstract

This review provides an overview of recent advances in multi-wavelength and multi-messenger observations of blazars, the current status of theoretical models for blazar emission, and prospects for future facilities. The discussion of observational results will focus on advances made possible through the Fermi Gamma-Ray Space Telescope and ground-based gamma-ray observatories (H.E.S.S., MAGIC, VERITAS), as well as the recent first evidence for a blazar being a source of IceCube neutrinos. The main focus of this review will be the discussion of our current theoretical understanding of blazar multi-wavelength and multi-messenger emission, in the spectral, time, and polarization domains. Future progress will be expected in particular through the development of the first X-ray polarimeter, IXPE, and the installation of the Cherenkov Telescope Array (CTA), both expected to become operational in the early to mid 2020s. Full article

(This article belongs to the Special Issue Cosmic Plasmas and Electromagnetic Phenomena)

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31 pages, 491 KiB

Open AccessArticle

Physics of “Cold” Disk Accretion onto Black Holes Driven by Magnetized Winds

by Sergey Bogovalov

Galaxies 2019, 7(1), 18; https://doi.org/10.3390/galaxies7010018 - 14 Jan 2019

Cited by 1 | Viewed by 3958

Abstract

Disk accretion onto black holes is accompanied by collimated outflows (jets). In active galactic nuclei (AGN), the kinetic energy flux of the jet (jet power or kinetic luminosity) may exceed the bolometric luminosity of the disk by a few orders of magnitude. This may be explained in the framework of the so called “cold” disk accretion. In this regime of accretion, the disk is radiatively inefficient because practically all the energy released at the accretion is carried out by the magnetized wind. This wind also provides efficient loss of the angular momentum by the matter in the disk. In this review, the physics of the accretion driven by the wind is considered from first principles. It is shown that the magnetized wind can efficiently carry out angular momentum and energy of the matter of the disk. The conditions when this process dominates conventional loss of the angular momentum due to turbulent viscosity are discussed. The “cold” accretion occurs when the viscous stresses in the disk can be neglected in comparison with impact of the wind on the accretion. Two problems crucial for survival of the model of “cold” accretion are considered. The first one is existence of the magnetohydrodynamical solutions for disk accretion purely due to the angular momentum loss by the wind. Another problem is the ability of the model to reproduce observations which demonstrate existence of the sources with kinetic power of jets 2–3 orders of magnitude exceeding the bolometric luminosity of disks. The solutions of the problem in similar prescriptions and numerical solutions without such an assumption are discussed. Calculations of the “unavoidable” radiation from the “cold” disk and the ratio of the jet power of the SMBH to the bolometric luminosity of the accretion disk around a super massive black hole are given in the framework of the Shakura and Sunyaev paradigm of an optically thick

α

-disk. The exploration of the Fundamental Plane of Black Holes allows us to obtain semi empirical equations that determine the bolometric luminosity and the ratio of the luminosities as functions of the black hole mass and accretion rate. Full article

(This article belongs to the Special Issue Cosmic Plasmas and Electromagnetic Phenomena)

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15 pages, 830 KiB

Open AccessArticle

Theoretical Discourse on Producing High Temporal Yields of Nuclear Excitations in Cosmogenic ²⁶Al with a PW Laser System: The Pathway to an Astrophysical Earthbound Laboratory

by Klaus Michael Spohr, Domenico Doria and Bradley Stewart Meyer

Galaxies 2019, 7(1), 4; https://doi.org/10.3390/galaxies7010004 - 26 Dec 2018

Cited by 1 | Viewed by 2973

Abstract

The development of the 10 PW laser system at the Extreme Light Infrastructure is a crucial step towards the realization of an astrophysical Earthbound laboratory. The interaction of high-power laser pulses with matter results in ultrashort (fs-ps) pulses of 10s of MeV ions and radiation that can create plasma and induce nuclear reactions therein. Due to the high fluxes of reaction-driving beam pulses, high yields of radioactive target nuclei in their ground and excited states can be provided in situ on short time scales. Cosmogenic ²⁶Al, which is of pronounced astrophysical interest, is a prime candidate for evaluating these new experimental possibilities. We describe how, for a short duration of

Δ t \sim 200 ps

, laser-driven protons with energies above

E_{p} \sim 5 MeV

can induce the compound nucleus reaction ²⁶Mg(p, n)²⁶Al leading to high and comparable yields of the three lowest-lying states in ²⁶Al including the short-lived,

t_{1 / 2}

= 1.20 ns state at 417 keV. In the aftermath of the reaction, for a short duration of

t \sim ns

, the yield ratios between the ground and the two lowest-lying excited states will resemble those present at thermodynamic equilibrium at high temperatures, thus mimicking high ²⁶Al entropies in cold environments. This can be seen as a possible first step towards an investigation of the interplay between those states in plasma environments. Theory suggests an intricate coupling of the ground state ²⁶Al_g.s. and the first excited isomer ^26mAl via higher-lying excitations such as the

J = 3^{+}

state at 417 keV resulting in a dramatic reduction of the effective lifetime of ²⁶Al which will influence the isotope’s abundance in our Galaxy. Full article

(This article belongs to the Special Issue Cosmic Plasmas and Electromagnetic Phenomena)

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Review

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23 pages, 427 KiB

Open AccessReview

The Origin of the Most Energetic Galactic Cosmic Rays: Supernova Explosions into Massive Star Plasma Winds

by Peter L. Biermann, Philipp P. Kronberg, Michael L. Allen, Athina Meli and Eun-Suk Seo

Galaxies 2019, 7(2), 48; https://doi.org/10.3390/galaxies7020048 - 14 Apr 2019

Cited by 7 | Viewed by 3743

Abstract

We propose that the high energy Cosmic Ray particles up to the upturn commonly called the ankle, from around the spectral turn-down commonly called the knee, mostly come from Blue Supergiant star explosions. At the upturn, i.e., the ankle, Cosmic Rays probably switch to another source class, most likely extragalactic sources. To show this we recently compiled a set of Radio Supernova data where we compute the magnetic field, shock speed and shock radius. This list included both Blue and Red Supergiant star explosions; both data show the same magnetic field strength for these two classes of stars despite very different wind densities and velocities. Using particle acceleration theory at shocks, those numbers can be transformed into characteristic ankle and knee energies. Without adjusting any free parameters both of these observed energies are directly indicated by the supernova data. In the next step in the argument, we use the Supernova Remnant data of the starburst galaxy M82. We apply this analysis to Blue Supergiant star explosions: The shock will race to their outer edge with a magnetic field that is observed to follow over several orders of magnitude

B (r) \times r \sim c o n s t .

, with in fact the same magnetic field strength for such stellar explosions in our Galaxy, and other galaxies including M82. The speed is observed to be ∼0.1 c out to about

10^{16} cm

radius in the plasma wind. The Supernova shock can run through the entire magnetic plasma wind region at full speed all the way out to the wind-shell, which is of order parsec scale in M82. We compare and identify the Cosmic Ray spectrum in other galaxies, in the starburst galaxy M82 and in our Galaxy with each other; we suggest how Blue Supergiant star explosions can provide the Cosmic Ray particles across the knee and up to the ankle energy range. The data from the ISS-CREAM (Cosmic Ray Energetics and Mass Experiment at the International Space Station) mission will test this cosmic ray concept which is reasonably well grounded in two independent radio supernova data sets. The next step in developing our understanding will be to obtain future more accurate Cosmic Ray data near to the knee, and to use unstable isotopes of Cosmic Ray nuclei at high energy to probe the “piston” driving the explosion. We plan to incorporate these data with the physics of the budding black hole which is probably forming in each of these stars. Full article

(This article belongs to the Special Issue Cosmic Plasmas and Electromagnetic Phenomena)

31 pages, 8173 KiB

Open AccessEditor’s ChoiceReview

Numerical Simulations of Jets from Active Galactic Nuclei

by José-María Martí

Galaxies 2019, 7(1), 24; https://doi.org/10.3390/galaxies7010024 - 22 Jan 2019

Cited by 31 | Viewed by 9477

Abstract

Numerical simulations have been playing a crucial role in the understanding of jets from active galactic nuclei (AGN) since the advent of the first theoretical models for the inflation of giant double radio galaxies by continuous injection in the late 1970s. In the almost four decades of numerical jet research, the complexity and physical detail of simulations, based mainly on a hydrodynamical/magneto-hydrodynamical description of the jet plasma, have been increasing with the pace of the advance in theoretical models, computational tools and numerical methods. The present review summarizes the status of the numerical simulations of jets from AGNs, from the formation region in the neighborhood of the supermassive central black hole up to the impact point well beyond the galactic scales. Special attention is paid to discuss the achievements of present simulations in interpreting the phenomenology of jets as well as their current limitations and challenges. Full article

(This article belongs to the Special Issue Cosmic Plasmas and Electromagnetic Phenomena)

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14 pages, 1094 KiB

Open AccessReview

MHD Accretion Disk Winds: The Key to AGN Phenomenology?

by Demosthenes Kazanas

Galaxies 2019, 7(1), 13; https://doi.org/10.3390/galaxies7010013 - 10 Jan 2019

Cited by 7 | Viewed by 3741

Abstract

Accretion disks are the structures which mediate the conversion of the kinetic energy of plasma accreting onto a compact object (assumed here to be a black hole) into the observed radiation, in the process of removing the plasma’s angular momentum so that it can accrete onto the black hole. There has been mounting evidence that these structures are accompanied by winds whose extent spans a large number of decades in radius. Most importantly, it was found that in order to satisfy the winds’ observational constraints, their mass flux must increase with the distance from the accreting object; therefore, the mass accretion rate on the disk must decrease with the distance from the gravitating object, with most mass available for accretion expelled before reaching the gravitating object’s vicinity. This reduction in mass flux with radius leads to accretion disk properties that can account naturally for the AGN relative luminosities of their Optical-UV and X-ray components in terms of a single parameter, the dimensionless mass accretion rate. Because this critical parameter is the dimensionless mass accretion rate, it is argued that these models are applicable to accreting black holes across the mass scale, from galactic to extragalactic. Full article

(This article belongs to the Special Issue Cosmic Plasmas and Electromagnetic Phenomena)

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18 pages, 669 KiB

Open AccessReview

Generation and Transport of Magnetic Flux in Accretion–Ejection Flows

by Ioannis Contopoulos

Galaxies 2019, 7(1), 12; https://doi.org/10.3390/galaxies7010012 - 9 Jan 2019

Cited by 2 | Viewed by 2887

Abstract

Astrophysical accretion flows are associated with energetic emission of radiation and outflows (winds and jets). Extensive observations of these two processes in X-ray binary outbursts are available. A convincing understanding of their dynamics remains, however, elusive. The main agent that controls the dynamics is believed to be a large scale magnetic field that threads the system. We propose that during the quiescent state, the field is held in place by a delicate balance between inward advection and outward diffusion through the accreting matter. We also propose that the source of the field is a growing toroidal electric current generated by the aberrated radiation pressure on the innermost plasma electrons in orbit around the central black hole. This is the astrophysical mechanism of the Cosmic Battery. When the return magnetic field outside the toroidal electric current diffuses through the surrounding disk, the disk magnetic field and its associated accretion rate gradually increase, thus leading the system to an outburst. After the central accretion flow approaches equipartition with radiation, it is disrupted, and the Cosmic Battery ceases to operate. The outward field diffusion is then reversed, magnetic flux reconnects with the flux accumulated around the central black hole and disappears. The magnetic field and the associated accretion rate slowly decrease, and the system is gradually driven back to quiescence. We conclude that the action (or inaction) of the Cosmic Battery may be the missing key that will allow us to understand the long-term evolution of astrophysical accretion–ejection flows. Full article

(This article belongs to the Special Issue Cosmic Plasmas and Electromagnetic Phenomena)

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14 pages, 665 KiB

Open AccessReview

Evidence for Helical Magnetic Fields Associated with AGN Jets and the Action of a Cosmic Battery

by Denise Gabuzda

Galaxies 2019, 7(1), 5; https://doi.org/10.3390/galaxies7010005 - 27 Dec 2018

Cited by 30 | Viewed by 5196

Abstract

Theoretical models for the electromagnetic launching of astrophysical jets have long indicated that this process should generate helical magnetic fields, which should then propagate outward with the jet plasma. Polarization observations of jets are key for testing this idea, since they provide direct information about the magnetic field structures in the synchrotron-emitting radio jets. Together with Faraday rotation measurements, it is possible in some cases to reconstruct the three-dimensional magnetic-field structure. There is now plentiful evidence for the presence of helical magnetic fields associated with the jets of active galactic nuclei, most directly the detection of transverse Faraday-rotation gradients indicating a systematic change in the line-of-sight magnetic field component across the jets. A variety of models involving helical jet magnetic fields have also been used to explain a great diversity of phenomena, including not only the linear polarization and Faraday rotation structures, but also circular polarization, anomalous wavelength dependences of the linear polarization, variability of jet ridge lines, variability of the Faraday rotation sign and polarization angle rotations. A joint consideration of Faraday rotation measurements on parsec and kiloparsec scales indicates a magnetic-field and current structure similar to that of a co-axial cable, suggesting the action of some kind of battery mechanism, such as the Poynting–Robertson cosmic battery. Full article

(This article belongs to the Special Issue Cosmic Plasmas and Electromagnetic Phenomena)

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