Skip to main content Accessibility help
×
  1. Home
  2. Browse subjects
  3. Physics and Astronomy
  4. Astronomy: General Interest
  5. Content Listing

Refine search

Refine search

Access:
Content type:
Publication date:
Apply   From and To filters
Subject: Show more
Journals Show more
Publishers: Show more
Societies Show more
Series: Show more
Collections: Show more

Actions for selected content:

Select all | Deselect all
  • View selected items
  • Export citations
  • Download PDF (zip)
  • Save to Kindle
  • Save to Dropbox
  • Save to Google Drive

Save Search

You can save your searches here and later view and run them again in "My saved searches".

Please provide a title, maximum of 40 characters.
Cancel
×

25644 results in Astronomy: General Interest

Page 210 of 1283

  • Numerical methods for General Relativistic particles

  • Fabio Bacchini, Bart Ripperda, Alexander Y. Chen, Lorenzo Sironi
  • Journal:
    Proceedings of the International Astronomical Union / Volume 14 / Issue S342 / May 2018
    Published online by Cambridge University Press:
    07 April 2020, pp. 19-23
    Print publication:
    May 2018
    • Article
      • You have access
    • PDF
    • Export citation

  • We present recent developments on numerical algorithms for computing photon and particle trajectories in the surrounding of compact objects. Strong gravity around neutron stars or black holes causes relativistic effects on the motion of massive particles and distorts light rays due to gravitational lensing. Efficient numerical methods are required for solving the equations of motion and compute i) the black hole shadow obtained by tracing light rays from the object to a distant observer, and ii) obtain information on the dynamics of the plasma at the microscopic scale. Here, we present generalized algorithms capable of simulating ensembles of photons or massive particles in any spacetime, with the option of including external forces. The coupling of these tools with GRMHD simulations is the key point for obtaining insight on the complex dynamics of accretion disks and jets and for comparing simulations with upcoming observational results from the Event Horizon Telescope.

  • High-dynamic-range 21 cm JVLA observations of the Perseus Cluster

  • Charles L. H. Hull
  • Journal:
    Proceedings of the International Astronomical Union / Volume 14 / Issue S342 / May 2018
    Published online by Cambridge University Press:
    07 April 2020, pp. 53-54
    Print publication:
    May 2018
    • Article
      • You have access
    • PDF
    • Export citation

  • We present 21 cm (L-band) JVLA observations of the Perseus Cluster, comprising data from all four array configurations. The resulting images are nearly an order of magnitude deeper than any other image made of NGC 1275 and its environs at this frequency.

Bayesian Astrophysics
  • Edited by Andrés Asensio Ramos, Íñigo Arregui
  • Published online:
    28 April 2018
    Print publication:
    26 April 2018
  • Bayesian methods are being increasingly employed in many different areas of research in the physical sciences. In astrophysics, models are used to make predictions to be compared to observations. These observations offer information that is incomplete and uncertain, so the comparison has to be pursued by following a probabilistic approach. With contributions from leading experts, this volume covers the foundations of Bayesian inference, a description of computational methods, and recent results from their application to areas such as exoplanet detection and characterisation, image reconstruction, and cosmology. It appeals to both young researchers seeking to learn about Bayesian methods as well as to astronomers wishing to incorporate these approaches in their research areas. It provides the next generation of researchers with the tools of modern data analysis that are already becoming standard in current astrophysical research.

Astrobiology, Discovery, and Societal Impact
  • Steven J. Dick
  • Published online:
    26 April 2018
    Print publication:
    03 May 2018
  • The search for life in the universe, once the stuff of science fiction, is now a robust worldwide research program with a well-defined roadmap probing both scientific and societal issues. This volume examines the humanistic aspects of astrobiology, systematically discussing the approaches, critical issues, and implications of discovering life beyond Earth. What do the concepts of life and intelligence, culture and civilization, technology and communication mean in a cosmic context? What are the theological and philosophical implications if we find life - and if we do not? Steven J. Dick argues that given recent scientific findings, the discovery of life in some form beyond Earth is likely and so we need to study the possible impacts of such a discovery and formulate policies to deal with them. The remarkable and often surprising results are presented here in a form accessible to disciplines across the sciences, social sciences, and humanities.

Cosmic Magnetic Fields
  • Edited by Jorge Sánchez Almeida, María Jesús Martínez González
  • Published online:
    21 April 2018
    Print publication:
    12 April 2018
  • Magnetic fields pervade the universe and play an important role in many astrophysical processes. However, they require specialised observational tools, and are challenging to model and understand. This volume provides a unified view of magnetic fields across astrophysical and cosmological contexts, drawing together disparate topics that are rarely covered together. Written by the lecturers of the XXV Canary Islands Winter School, it offers a self-contained introduction to cosmic magnetic fields on a range of scales. The connections between the behaviours of magnetic fields in these varying contexts are particularly emphasised, from the relatively small and close ranges of the Sun, planets and stars, to galaxies and clusters of galaxies, as well as on cosmological scales. Aimed at young researchers and graduate students, this up-to-date review uniquely brings together a subject often tackled by disconnected communities, conveying the latest advances as well as highlighting the limits of our current understanding.

  • 3 - Stellar Magnetic Fields

  • Edited by Jorge Sánchez Almeida, Instituto de Astrofísica de Canarias, Tenerife, María Jesús Martínez González, Instituto de Astrofísica de Canarias, Tenerife
  • Book:
    Cosmic Magnetic Fields
    Published online:
    21 April 2018
    Print publication:
    12 April 2018, pp 47-86

  • Summary

    Abstract

    Recent developments in astrophysical spectropolarimetry have significantly expanded our understanding of stellar magnetism. Using modern instrumentation and data analysis methods it is becoming possible to detect and characterise surface magnetic fields not just for a few peculiar objects but for essentially all types of stars, ranging from massive OB stars to brown dwarfs. The intention of this chapter is to give a general overview of the stellar magnetic field diagnostic methods and to present results of the application of these methods to different classes of stars. First, the chapter discusses the physical processes that lead to appearance of magnetic signatures in stellar spectra. Based on this discussion, the most commonly used magnetic observables are introduced for the intensity and polarisation spectra. The methods of interpretation of magnetic measurements, starting with robust field detection techniques and leading to reconstruction of the physically realistic vector maps of surface magnetic fields, are discussed. Finally, the current knowledge about the incidence, geometries and the origin of magnetic fields in stars of different masses and ages is reviewed and the astrophysical significance of magnetism in the context of stellar structure and evolution is discussed.

    Introduction

    This chapter presents an introduction to the studies of stellar magnetic fields. We explore the questions of how magnetic fields can be detected on the stellar surfaces, what information about magnetic field topologies can be extracted from different observations, and what are the observed properties of magnetic fields in stars of different masses and ages. The origin of magnetism in different types of stars and its relation to other physical processes operating in stellar interiors and atmospheres are briefly discussed.

    The following sections start by presenting the essential theoretical foundations of the stellar magnetic field diagnostic and modelling. We consider the Zeeman effect in spectral lines and information contained in the polarisation characteristics of stellar radiation. A connection between the local magnetic field parameters and morphology of the stellar polarisation profiles is established using both detailed numerical calculations and simplified analytical considerations. Based on this discussion, we introduce different methodologies suitable for the detection and characterisation of stellar magnetic fields.

  • Preface

  • Edited by Jorge Sánchez Almeida, Instituto de Astrofísica de Canarias, Tenerife, María Jesús Martínez González, Instituto de Astrofísica de Canarias, Tenerife
  • Book:
    Cosmic Magnetic Fields
    Published online:
    21 April 2018
    Print publication:
    12 April 2018, pp xiii-xiii

  • Summary

    Magnetic fields play an important role in many astrophysical processes. They are difficult to detect and characterize because often their properties have to be inferred through interpreting the polarization of the light. Magnetic fields are also challenging to model and understand. Magnetized plasmas behave following highly non-linear differential equations having no general solution, so that every astrophysical problem represents a special case to be studied independently. Hence, magnetic fields are often an inconvenient subject that is overlooked or simply neglected (the elephant in the room, as they are dubbed on posters in the XXV Canary Islands Winter School of Astrophysics). Such a difficulty burdens the research on magnetic fields, which has evolved to become a very technical subject, with many small disconnected communities studying specific aspects and details. The school tried to amend the situation by providing a unifying view of the subject. The students had a chance to understand the behavior of magnetic fields in all astrophysical contexts, from cosmology to the Sun, and from starbursts to AGNs. The school was planned to present a balanced yet complete review of our knowledge, with excursions into the unknown to point out present and future lines of research.

    The subject of Cosmic Magnetic Fields was split into seven different topics: cosmic magnetic field essentials, solar magnetic fields, stellar magnetic fields, the role of magnetic fields on AGN feedback, magnetic fields in galaxies, magnetic fields in galaxy clusters and at larger scales, and primordial magnetic fields and magnetic fields in the early Universe. The corresponding lectures were delivered by seven well known and experienced scientists that have played key roles in the major advances of the field during the last years: F. Cattaneo, P. Judge, O. Kochukhov, R. Keppens, R. Beck, K. Dolag, and F. Finelli. Their lectures were recorded and are freely available at the IAC website: http://iactalks.iac.es/talks/serie/19. Together with the reviews included in the present volume, they form a unique resource for both students and professional researchers. They provide a global view of this very compartmentalized, yet fundamental, field of research.

  • 5 - Magnetic Fields in Galaxies

    • By Rainer Beck, Max Planck Institut für Radioastronomie, Germany
  • Edited by Jorge Sánchez Almeida, Instituto de Astrofísica de Canarias, Tenerife, María Jesús Martínez González, Instituto de Astrofísica de Canarias, Tenerife
  • Book:
    Cosmic Magnetic Fields
    Published online:
    21 April 2018
    Print publication:
    12 April 2018, pp 123-160

  • Summary

    Introduction

    Magnetism is a fundamental force with special properties.

  • • Most baryonic matter is ionized. Magnetic fields are easy to generate.

  • • Magnetic monopoles do not exist or are extremely rare. Magnetic fields are hard to destroy.

  • • Magnetic fields need illumination. Magnetic fields are difficult to observe.

    • The scarceness of data leaves many questions on cosmic magnetic fields.

  • • When and how were the first fields generated?

  • • Did significant fields exist before galaxies formed?

  • • How and how fast were the fields amplified?

  • • How did fields affect the evolution of stars, planets, galaxies and galaxy clusters?

  • • How strongly is intergalactic space magnetized?

    • Magnetic fields are often ignored in astrophysics, in particular in models of galaxies and the interstellar medium (ISM), although they are a major agent in the ISM and in galaxy halos, and important for the structure and evolution of galaxies.

  • • Magnetic fields contribute significantly to the total pressure which balances the gas disk of galaxies against gravitation (Fletcher & Shukurov, 2001).

  • • Magnetic turbulence distributes energy from supernova explosions within the ISM (Subramanian, 1998).

  • • Magnetic reconnection is a possible heating source for the ISM and halo gas (Birk et al., 1998).

  • • Magnetic fields increase angular momentum transport and hence the gas inflow rate in barred galaxies (Beck et al., 2005; Kim & Stone, 2012).

  • • Magnetic fields affect the dynamics of the turbulent ISM (de Avillez & Breitschwerdt, 2005) and the gas flows in spiral arms (Gómez & Cox, 2002).

  • • Magnetic fields make the gaseous spiral arms more patchy and drive gas outflows into the halo (Pakmor & Springel, 2013).

  • • The shock strength in spiral density waves is decreased and structure formation is reduced in the presence of strong fields (Dobbs & Price, 2008; Fletcher et al., 2011).

  • • Magnetic fields stabilize gas clouds and reduce the star-formation efficiency to the observed low values (Vázquez-Semadeni et al., 2005; Price & Bate, 2008).

  • • Magnetic fields are essential for the onset of star formation as they enable the removal of angular momentum from the protostellar cloud via ambipolar diffusion (Heitsch et al., 2004).

Page 210 of 1283