346 research outputs found
The Black Hole Remnant of Black Hole-Neutron Star Coalescing Binaries
No full textWe present a model for determining the dimensionless spin parameter and mass of the black hole remnant of black hole-neutron star mergers with parallel orbital angular momentum and initial black hole spin. This approach is based on the Buonanno, Kidder, and Lehner method for binary black holes and it is successfully tested against the results of numerical-relativity simulations: the dimensionless spin parameter is predicted with absolute error , whereas the relative error on the final mass is %, its distribution being pronouncedly peaked at 1%. Our approach and the fit to the torus remnant mass reported in Foucart (2012) thus constitute an easy-to-use analytical model that accurately describes the remnant of BH-NS mergers. We investigate the space of parameters consisting of the binary mass ratio, the initial black hole spin, and the neutron star mass and equation of state. We provide indirect support to the cosmic censorship conjecture for black hole remnants of black hole-neutron star mergers. We show that the presence of a neutron star affects the quasi-normal mode frequency of the black hole remnant, thus suggesting that the ringdown epoch of the gravitational wave signal may virtually be used to (1) distinguish binary black hole from black hole-neutron star mergers and to (2) constrain the neutron star equation of state
Prospects for joint gravitational-wave and electromagnetic observations of neutron-star-black-hole coalescing binaries
No full textCoalescing neutron-star-black-hole (NS-BH) binaries are a promising source of gravitational-wave (GW) signals detectable with large-scale laser interferometers such as the Advanced Laser Interferometer Gravitational-Wave Observatory and Virgo. They are also one of the main short gamma-ray burst (SGRB) progenitor candidates. If the black hole (BH) tidally disrupts its companion, an SGRB may be ignited when a sufficiently massive accretion disk forms around the remnant BH. Detecting an NS-BH coalescence both in the GW and electromagnetic (EM) spectrum offers a wealth of information about the nature of the source. How much can actually be inferred from a joint detection is unclear, however, as a mass/spin degeneracy may reduce the GW measurement accuracy. To shed light on this problem and on the potential of joint EM+GW observations, we here combine recent semi-analytical predictions for the remnant disk mass with estimates of the parameter-space portion that is selected by a GW detection. We identify cases in which an SGRB ignition is supported, others in which it can be excluded, and finally others in which the outcome depends on the chosen model for the currently unknown NS equation of state. We pinpoint a range of systems that would allow us to place lower bounds on the equation of state stiffness if both the GW emission and its EM counterpart are observed. The methods we develop can broaden the scope of existing GW detection and parameter-estimation algorithms and could allow us to disregard about half of the templates in an NS-BH search following an SGRB trigger, increasing its speed and sensitivity
Ambulatory blood pressure in patients with glaucoma.
No full textPurpose: Any clinical condition causing hypoperfusion at the level of optic nerve head represents a risk factor for the developing of glaucoma damage. In most normal subjects is observed that diurnal blood pressure curve presents night"dip" (about 12% of day-time values). Methods: We assessed the influence of the circadian blood pressure (BP) profile on the presence of visual field defects (VFD) in patients with glaucoma. We performed masked assessment of visual field and 24-hour noninvasive ambulatory BP monitiring (spacelabs 90207 recorder) in 3 groups of patients: 1) twenty patients with myopia and open angle glaucoma (MOAG); 2) twenty patients with primary openangle glaucoma (POAG); 3) nine patients with normal tension glaucoma. A fourth group of fifteen ealthy normotensive volunteers had its BP monitored as reference controls. Results: Our samples of MOAG, POAG and NTG had lower ambulatory day and night BP values than normotensive controls, even if the differences were not statistically significant. Considering all the groups we observed that patients with progressive VFD have night sistolic "dip" higher than patients with stable VFD (Kruskas Wallis test: p.= 0.01). This feeding could influence the progression of the glaucomatouse disease in these patients, as it can be inferred from a correlation between low systolic night BP values and VFD (R.=0.4). Conclusion: Arterial blood pressure values lower than healthy normotensive subjects can be considered as risk factor in the progression of VFD in glaucomatous patients. An exagerated must be considered in patients presenting evolutive glaucoma damage
BLACK HOLE-NEUTRON STAR COALESCING BINARIES
No full textCoalescing black hole-neutron star binaries have been invoked as possible progenitors of short gamma-ray bursts and are also among the most promising gravitational wave sources to be detected by ground-based laser interferometers. When the star is disrupted by tidal interactions before reaching the innermost stable circular orbit, the gravitational wave signal emitted by the system is expected to exhibit a cutoff frequency which is a distinctive feature of the waveform. We evaluate this frequency for several equations of state, describing the matter inside the neutron star, and combinations of the binary parameters. We show that, if this frequency will be found in a detected gravitational wave, it will provide valuable information on the behavior of matter in the stellar core
Rischi pandemici
No full textThe author intends to use Niklas Luhmann’s social systems theory, and namely his sociology of risk, to assess the effects of the pandemic on crucial social communication systems, such as politics, mass media, economics, science, law, and love. Moving from the primary distinction between dangers and risks, the paper describes the transformation of pandemic dangers into risky decisions within each social communication system
Cinema e diritto: un confronto impossibile?
No full textThe author describes the mutual observation processes that take place between cinema and law.
Cinema has represented the law in many of its aspects, it has played a role in guiding public opinion
regarding the law, it has contributed to denouncing situations of discrimination and violation of
rights. On the other hand, the law has mainly performed a function of normalizing cinematographic
works, using both its coercive tools and its incentive tools. The last part of the work describes what
has changed in this relationship in the streaming era
Black hole-neutron star mergers and short gamma-ray bursts: A relativistic toy model to estimate the mass of the torus
No full textThe merger of a binary system composed of a black hole (BH) and a neutron star (NS) may leave behind a torus of hot, dense matter orbiting around the BH. While numerical-relativity simulations are necessary to simulate this process accurately, they are also computationally expensive and unable at present to cover the large space of possible parameters, which include the relative mass ratio, the stellar compactness, and the BH spin. To mitigate this and provide a first reasonable coverage of the space of parameters, we have developed a method for estimating the mass of the remnant torus from BH-NS mergers. The toy model makes use of an improved relativistic affine model to describe the tidal deformations of an extended tri-axial ellipsoid orbiting around a Kerr BH and measures the mass of the remnant torus by considering which of the fluid particles composing the star are on bound orbits at the time of the tidal disruption. We tune the toy model by using the results of fully general-relativistic simulations obtaining relative precisions of a few percent and use it to investigate the space of parameters extensively. In this way, we find that the torus mass is largest for systems with highly spinning BHs, small stellar compactnesses, and large mass ratios. As an example, tori as massive as M-b,M-tor similar or equal to 1.33 M-circle dot can be produced for a very extended star with compactness C similar or equal to 0.1 inspiralling around a BH with dimensionless spin parameter a = 0.85 and mass ratio q similar or equal to 0.3. However, for a more astrophysically reasonable mass ratio q similar or equal to 0.14 and a canonical value of the stellar compactness C similar or equal to 0.145, the toy model sets a considerably smaller upper limit of M-b,M-tor less than or similar to 0.34 M-circle dot
La sfida dei diritti umani
No full textIl contributo descrive il significato e la portata dei diritti umani da un punto di vista sociologico, quali temi di comunicazione del sottosistema giuridico rispetto ad altri sottosistemi sociali
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