Found 16 talks width keyword black holes

Video
Tuesday March 11, 2014
Dr. Martin López Corredoira
IAC

Abstract

1) López-Corredoira & Gutiérrez (2012, RAA, 12, 249): Extremely luminous QSOs exist at high redshift but they are absent at low redshift. Our analyses show that it is not due to any significant evolution of black hole masses or Eddington ratios for equal luminosity QSOs, so the problem can be translated into a "Why are not there QSOs with very high black hole masses at low redshift?". 2) López-Corredoira & Perucho (2012, A&A, 544, 56): The MOJAVE survey contains 101 quasars with a total of 354 observed radio components that are different from the radio cores, among which 95% move with apparent projected superluminal velocities with respect to the core, and 45% have projected velocities larger than 10c (with a maximum velocity 60c). Relativistic Doppler boosting explains these apparent anomalies, but it requires a huge average kinetic power to produce such powerful ejections: ~7×10^{47} erg/s, a significant portion of the Eddington luminosity and on the order of the bolometric luminosity. This amount is much higher than previous estimates of kinetic power on kpc-scales. 3) There are many other pending problems in QSOs in the literature (review at López-Corredoira 2011, IJAA, 1, 73): the different structure of the clouds along the QSO's line of sight and their tangential directions; the spatial correlation between QSOs and galaxies; inconsistencies in the AGN unification model; etc.


Video
Thursday November 28, 2013
Prof. Michiel van der Klis
Astronomical Institute, University Amsterdam, the Netherlands

Abstract

The matter within a few Schwarzschild radii of accreting neutron stars and black holes is moving under the influence of a strong gravitational field, and, in stellar mass compact objects, through strongly curved spacetime. The X-rays emitted in the accretion process can be used to diagnose this motion, using both spectroscopy and rapid time variability. Similarly, X-rays emitted from the surface of accreting neutron stars can be used to diagnose neutron star mass, radius and even internal structure. I discuss these ways to probe strong gravitational fields and ultradense matter from an empirical perspective and in the context of proposed future X-ray observatories, in particular, LOFT.


Video
Thursday July 4, 2013
Dr. Tom Maccarone
Texas Tech University

Abstract

In the past few years, a series of discoveries have been made of objects which appear to be accreting stellar mass black holes in globular clusters -- both in the Milky Way and in other nearby galaxies. I will discuss why the theoretical work which suggested that such objects would be unlikely to exist, the observations showing they do exist, some of the unusual aspects of some of the individual sources, and the new theoretical framework for producing them.


Video
Tuesday April 9, 2013
Dr. Teodoro Muñoz Darias
University of Southampton

Abstract

X-ray observations performed by several missions during the last few decades have provided a very large data base on black hole X-ray binaries. Many of these objects are transient systems that spend most part of their lives in quiescence, showing occasional outburst where their luminosity increases up to eight orders of magnitude. I will review the state-of-the-art in the field, focussing on the different accretion regimes observed in these sources. In the second part of the talk I will concentrate on the influence that the orbital inclination (i.e., viewing angle) has in the spectral properties of black hole binaries, with emphasis on the detection of relativistic effects in the inner accretion flow surrounding the black hole.


Video
Wednesday March 6, 2013
Dr. Jesús Corral Santana
IAC

Abstract

X-ray transients are binary systems composed by a 'normal' star which is transfering mass onto a compact object (either a black hole or a neutron star) through Roche lobe overflow. These systems show sporadic outburst episodes and long quiescence states, being ideal systems to search for stellar-mass black holes. Different studies predict a Galactic population of ~10^3-10^4 X-ray transients, however, there are only 18 stellar-mass black holes dynamically confirmed (and other ~32 candidates whichc share similar timing and spectral properties).

In this talk I'll present the case of Swift J1357.2-0933, a new X-ray transient discovered in 2011. Our analysis shows that Swift J1357.2-0933 is the first black hole transient seen at a large inclination (>75º). High time resolution lightcurves show dips or eclipses produced by a vertical structure present in the inner accretion rather than the companion star. Some dips display up to ~50% reduction of flux in ~2min (~30% reduction of flux in 7s). Moreover, the dips present a recurrence period of a few minutes which increases with time. This can only be explained by the expansion of the obscuring structure outward in the accretion. Swift J1357.2-0933 could be the prototype of an hytherto Galactic population of black hole transients with large inclinations.


Video
Tuesday June 5, 2012
Dr. Emanuele Farina
Università dell'Insubria & INFN Milano Bicocca; Italy

Abstract

KS 1222+216 (redshift z=0.432) is a FSRQ that in the gamma energy range, has shown a particularly active behaviour with flares also in the Very High Energy domain (e.g. E > 100 GeV). MAGIC detect a flare in June 2010, in cincidence with a huge GeV emission recorded by AGILE and Fermi. PKS 1222+216 is thus the third FSRQ, after 3C279 (z=0.536) and PKS 1510-089 (z=0.36), observed at such high energy. We investigate the optical spectral properties of this blazar during a period of more than 3 years. While the continuum is highly variable the broad line emission is practically constant. This supports a scenario in which the broad line region is not affected by jet continuum variations. We thus infer the thermal component of the continuum from the line luminosity and we show that it is comparable with the continuum level observed during the phases of minimum optical activity. We can thus estimate, also in the case of an extremly variable object, the mass of the black hole through the virial method from the FWHM of MgII, HBeta, and HAlpha broad lines and from the thermal continuum luminosity. This yields a black hole mass value of ~6x10E8 solar masses.


Video
Thursday September 22, 2011
Prof. Joseph Lazio
Jet Propulsion Laboratory, USA

Abstract

The Square Kilometre Array is intended to be the centimeter- and meter-wavelength telescope for the 21st Century. Originally proposed as the "hydrogen telescope," the science case is now recognized to be much broader, and the SKA will address fundamental questions in astrophysics, physics, and astrobiology. The international science community has developed a set of Key Science Programs: (1) Emerging from the Dark Ages and the Epoch of Reionization; (2) Galaxy Evolution, Cosmology, and Dark Energy; (3) The Origin and Evolution of Cosmic Magnetism; (4) Strong Field Tests of Gravity Using Pulsars and Black Holes; and (5) The Cradle of Life & Astrobiology. I highlight how the SKA's Key Science Programs will be an integral component of the multi-wavelength, multi-messenger frontiers for astronomy and how the science pathfinding for the SKA is beginning now.


Video
Friday May 20, 2011
Prof. Ramesh Narayan
Harvard-Smithsonian Center, USA.

Abstract

In his public talk, Prof. Narayan will summarize our knowledge of Black Holes in the universe. He will describe how Black Holes are discovered, how their properties are measured, and what the results mean. He will also discuss the many ways in which Black Holes influence their surroundings and the profound effect they have had on the evolution of the universe.


Video
Thursday May 19, 2011
Prof. Ramesh Narayan
Harvard-Smithsonian Center for Astrophysics, USA

Abstract

An astrophysical black hole is completely described with just two parameters: its mass and its dimensionless spin. A few dozen black holes have mass estimates, but until recently none had a reliable spin estimate. The first spins have now been measured for black holes in X-ray binaries. The talk will describe the method used to make these measurements and will discuss implications of the results obtained so far.


Video
Thursday November 4, 2010
Dr. Felix Mirabel
CEA, Service d'Astrophysique, France

Abstract

The so called "dark ages" of the universe began about 400.000 years after the Big Bang as matter cooled down and space became filled with neutral hydrogen for hundreds of millions years. How the Universe was heated and reionized during the first billion years after the Big Bang is a question of topical interest in cosmology. I will show that current theoretical models on the formation and collapse of primordial stars suggest that a large fraction of massive stars should have imploded, forming high-mass black hole X-ray binaries. Then, I will review the recent observations of compact stellar remnants in the near and distant universe that support this theoretical expectation, showing that the thermal (UV and soft X-rays) and non-thermal (hard X-rays, winds and jets) emission from a large population of stellar black holes in high mass binaries heated the intergalactic medium over large volumes of space, complementing the reionization by their stellar progenitors. Feedback from accreting stellar black holes at that epoch would have prevented the formation of the large quantities of low mass dwarf galaxies that are predicted by the cold dark matter model of the universe. A large population of black hole binaries may be important for future observations of gravitational waves as well as for the existing and future atomic hydrogen radio surveys of HI in the early universe.

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