93 research outputs found
The Evolution of Galaxies and Their Environment
The Third Teton Summer School on Astrophysics discussed the formation of galaxies, star formation in galaxies, galaxies and quasars at high red shift, and the intergalactic and intercluster medium and cooling flows. Observation and theoretical research on these topics was presented at the meeting and summaries of the contributed papers are included in this volume
Cosmic Plasmas and Electromagnetic Phenomena
During the past few decades, plasma science has witnessed a great growth in laboratory studies, in 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. 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 at the vicinities of black holes (i.e., their jets and accretion disks). Cosmic plasma phenomena can be studied with different methods, such as laboratory experiments, astrophysical observations, and theoretical/computational approaches (i.e., MHD, particle-in-cell simulations, etc.). They exhibit a multitude of complex magnetohydrodynamic behaviors, acceleration, radiation, turbulence, and various instability phenomena. This Special Issue addresses the growing need of the plasma science principles in astrophysics and presents our current understanding of the physics of astrophysical plasmas, their electromagnetic behaviors and properties (e.g., shocks, waves, turbulence, instabilities, collimation, acceleration and radiation), both microscopically and macroscopically. This Special Issue provides a series of state-of-the-art reviews from international experts in the field of cosmic plasmas and electromagnetic phenomena using theoretical approaches, astrophysical observations, laboratory experiments, and state-of-the-art simulation studies
Magnetorotational Collapse of Supermassive Stars: Black Hole Formation, Gravitational Waves and Jets
We perform MHD simulations in full GR of uniformly rotating stars that are
marginally unstable to collapse. Our simulations model the direct collapse of
supermassive stars (SMSs) to seed black holes (BHs) that can grow to become the
supermassive BHs at the centers of quasars and AGNs. They also crudely model
the collapse of massive Pop III stars to BHs, which could power a fraction of
distant, long gamma-ray bursts (GRBs). The initial stellar models we adopt are
polytropes seeded with a dynamically unimportant dipole magnetic
field (B field). We treat initial B-field configurations either confined to the
stellar interior or extending out from the interior into the stellar exterior.
The BH formed following collapse has mass (where is
the mass of the initial star) and spin . A massive,
hot, magnetized torus surrounds the remnant BH. At s following the gravitational wave
(GW) peak amplitude, an incipient jet is launched. The disk lifetime is s, and the jet luminosity is
ergs/s. If of this power is converted into gamma rays, SWIFT
and FERMI could potentially detect these events out to large redshifts . Thus, SMSs could be sources of ultra-long GRBs and massive Pop III stars
could be the progenitors that power a fraction of the long GRBs observed at
redshift . GWs are copiously emitted during the collapse, and peak
at (),
i.e., in the LISA (DECIGO/BBO) band; optimally oriented SMSs could be
detectable by LISA (DECIGO/BBO) at (). Hence
SMSs collapsing at are promising multimessenger
sources of coincident gravitational and electromagnetic waves.Comment: 14 pages, 9 figures, replaced with the published versio
Supernova-driven Turbulence and Magnetic Field Amplification in Disk Galaxies
Supernovae are known to be the dominant energy source for driving turbulence
in the interstellar medium. Yet, their effect on magnetic field amplification
in spiral galaxies is still poorly understood. Analytical models based on the
uncorrelated-ensemble approach predicted that any created field will be
expelled from the disk before a significant amplification can occur. By means
of direct simulations of supernova-driven turbulence, we demonstrate that this
is not the case. Accounting for vertical stratification and galactic
differential rotation, we find an exponential amplification of the mean field
on timescales of 100Myr. The self-consistent numerical verification of such a
"fast dynamo" is highly beneficial in explaining the observed strong magnetic
fields in young galaxies. We, furthermore, highlight the importance of rotation
in the generation of helicity by showing that a similar mechanism based on
Cartesian shear does not lead to a sustained amplification of the mean magnetic
field. This finding impressively confirms the classical picture of a dynamo
based on cyclonic turbulence.Comment: 99 pages, 46 figures (in part strongly degraded), 8 tables, PhD
thesis, University of Potsdam (2009). Resolve URN
"urn:nbn:de:kobv:517-opus-29094" (e.g. via
http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-29094) for a version with
high-resolution figure
National Astronomy Meeting 2019 Abstract Book
The National Astronomy Meeting 2019 Abstract Book. Abstracts accepted and presented, including both oral and poster presentations, at the Royal Astronomical Society's NAM2019 conference, held at Lancaster University between 30 June and 4 July 2019
Simulations of cosmic ray propagation
We review numerical methods for simulations of cosmic ray (CR) propagation on
galactic and larger scales. We present the development of algorithms designed
for phenomenological and self-consistent models of CR propagation in kinetic
description based on numerical solutions of the Fokker-Planck equation. The
phenomenological models assume a stationary structure of the galactic
interstellar medium and incorporate diffusion of particles in physical and
momentum space together with advection, spallation, production of secondaries
and various radiation mechanisms. The self-consistent propagation models of CRs
include the dynamical coupling of the CR population to the thermal plasma. The
CR transport equation is discretized and solved numerically together with the
set of magneto-hydrodynamic (MHD) equations in various approaches treating the
CR population as a separate relativistic fluid within the two-fluid approach or
as a spectrally resolved population of particles evolving in physical and
momentum space. The relevant processes incorporated in self-consistent models
include advection, diffusion and streaming well as adiabatic compression and
several radiative loss mechanisms.
We discuss applications of the numerical models for the interpretation of CR
data collected by various instruments. We present example models of
astrophysical processes influencing galactic evolution such as galactic winds,
the amplification of large-scale magnetic fields and instabilities of the
interstellar medium.Comment: 99 pages, 13 figures, to be published in the Living Reviews of
Computational Astrophysic
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