93 research outputs found

    Annual Report 2006

    Get PDF

    Annual Report 2008

    No full text

    The Evolution of Galaxies and Their Environment

    Get PDF
    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

    Annual Report 2009

    No full text

    Cosmic Plasmas and Electromagnetic Phenomena

    Get PDF
    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

    Get PDF
    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 Γ=4/3\Gamma = 4/3 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 MBH≃0.9MM_{BH} \simeq 0.9M (where MM is the mass of the initial star) and spin aBH/MBH≃0.7a_{BH}/M_{BH}\simeq 0.7. A massive, hot, magnetized torus surrounds the remnant BH. At Δt∼400−550M≈2000−2700(M/106M⊙)\Delta t\sim 400-550M\approx 2000-2700(M/10^6M_\odot)s following the gravitational wave (GW) peak amplitude, an incipient jet is launched. The disk lifetime is Δt∼105(M/106M⊙)\Delta t\sim 10^5(M/10^6M_\odot)s, and the jet luminosity is LEM∼1051−52L_{EM}\sim 10^{51-52} ergs/s. If ≳1−10%\gtrsim 1-10\% of this power is converted into gamma rays, SWIFT and FERMI could potentially detect these events out to large redshifts z∼20z\sim 20. 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 z∼5−8z \sim 5-8. GWs are copiously emitted during the collapse, and peak at ∼15(106M⊙/M)mHz\sim 15(10^6 M_{\odot}/M)\rm mHz (∼0.15(104M⊙/M)Hz\sim 0.15(10^4 M_{\odot}/M)\rm Hz), i.e., in the LISA (DECIGO/BBO) band; optimally oriented SMSs could be detectable by LISA (DECIGO/BBO) at z≲3z \lesssim 3 (z≲11z \lesssim 11). Hence 104M⊙10^4 M_{\odot} SMSs collapsing at z∼10z\sim 10 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

    Get PDF
    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

    Get PDF
    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

    Full text link
    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
    • …
    corecore