On September 14, 2015 at 09:50:45 UTC the two detectors of the Laser Interferometer Gravitational-Wave Observatory simultaneously observed a transient gravitational-wave signal. The signal sweeps upwards in frequency from 35 to 250 Hz with a peak gravitational-wave strain of 1.0×10(-21). It matches the waveform predicted by general relativity for the inspiral and merger of a pair of black holes and the ringdown of the resulting single black hole. The signal was observed with a matched-filter signal-to-noise ratio of 24 and a false alarm rate estimated to be less than 1 event per 203,000 years, equivalent to a significance greater than 5.1σ. The source lies at a luminosity distance of 410(-180)(+160)  Mpc corresponding to a redshift z=0.09(-0.04)(+0.03). In the source frame, the initial black hole masses are 36(-4)(+5)M⊙ and 29(-4)(+4)M⊙, and the final black hole mass is 62(-4)(+4)M⊙, with 3.0(-0.5)(+0.5)M⊙c(2) radiated in gravitational waves. All uncertainties define 90% credible intervals. These observations demonstrate the existence of binary stellar-mass black hole systems. This is the first direct detection of gravitational waves and the first observation of a binary black hole merger.

/pdf/the-observation-of-gravitational-waves-from-a-binary-black-58srpupgg9.pdf

The Observation of Gravitational Waves from a Binary Black Hole Merger

When all thermonuclear sources of energy are exhausted a sufficiently heavy star will collapse. Unless fission due to rotation, the radiation of mass, or the blowing off of mass by radiation, reduce the star's mass to the order of that of the sun, this contraction will continue indefinitely. In the present paper we study the solutions of the gravitational field equations which describe this process. In I, general and qualitative arguments are given on the behavior of the metrical tensor as the contraction progresses: the radius of the star approaches asymptotically its gravitational radius; light from the surface of the star is progressively reddened, and can escape over a progressively narrower range of angles. In II, an analytic solution of the field equations confirming these general arguments is obtained for the case that the pressure within the star can be neglected. The total time of collapse for an observer comoving with the stellar matter is finite, and for this idealized case and typical stellar masses, of the order of a day; an external observer sees the star asymptotically shrinking to its gravitational radius.

On Continued Gravitational Contraction

Local anisotropy in self-gravitating systems

We present distance measurements to 71 high redshift type Ia supernovae discovered during the first year of the 5-year Supernova Legacy Survey (SNLS). These events were detected and their multi-color light-curves measured using the MegaPrime/MegaCam instrument at the Canada-France-Hawaii Telescope (CFHT), by repeatedly imaging four one-square degree fields in four bands. Follow-up spectroscopy was performed at the VLT, Gemini and Keck telescopes to confirm the nature of the supernovae and to measure their redshift. With this data set, we have built a Hubble diagram extending to z = 1, with all distance measurements involving at least two bands. Systematic uncertainties are evaluated making use of the multiband photometry obtained at CFHT. Cosmological fits to this first year SNLS Hubble diagram give the following results: {Omega}{sub M} = 0.263 {+-} 0.042 (stat) {+-} 0.032 (sys) for a flat {Lambda}CDM model; and w = -1.023 {+-} 0.090 (stat) {+-} 0.054 (sys) for a flat cosmology with constant equation of state w when combined with the constraint from the recent Sloan Digital Sky Survey measurement of baryon acoustic oscillations.

The Supernova Legacy Survey: Measurement of Omega_m, Omega_l and w from the First Year Data Set

We calibrate reverberation-based black hole (BH) masses in active galactic nuclei (AGNs) by using the correlation between BH mass, MBH, and bulge/spheroid stellar velocity dispersion, σ*. We use new measurements of σ* for six AGNs and published velocity dispersions for 10 others, in conjunction with improved reverberation-mapping results, to determine the scaling factor required to bring reverberation-based BH masses into agreement with the quiescent galaxy MBH-σ* relationship. The scatter in the AGN BH masses is found to be less than a factor of 3. The current observational uncertainties preclude the use of the scaling factor to discriminate between broad-line region models.

/pdf/supermassive-black-holes-in-active-galactic-nuclei-ii-1ojdz32oq0.pdf

Supermassive black holes in active galactic nuclei. II. Calibration of the black hole mass-velocity dispersion relationship for active galactic nuclei

We study the role played by local anisotropy and radiation (in the free-streaming regime) in the onset of dynamical instabilities. In the case of anisotropy we find that, for Newtonian and post-Newtonian approximations, the relevant quantity is the anisotropy of the unperturbed fluid, and that small anisotropies may, in principle, drastically change the stability of the system. The influence of the free-streaming radiation upon stability appears to be qualitatively of the same type as that of radiative diffusion. Some speculations and prospective applications to astrophysical scenarios are presented

Dynamical instability for radiating anisotropic collapse

We study the role played by the shear and the shearing viscosity in the onset of dynamical instabilities. For both the Newtonian and the relativistic regimes, the shearing viscosity decreases the instability of the fluid. The corrections due to the shear, which appear only in the post-Newtonian approximation, decrease the range of values of the'ratio of specific heats'for which the system is unstable. This result is the consequence of the fact that the collapse with shear proceeds faster than the corresponding shear-free collapse. Under otherwise identical conditions, therefore, the material of the collapsing sphere with shear should be softer than the material of the shear-free collapsing sphere

/pdf/dynamical-instability-for-shearing-viscous-collapse-2h1swy9pzg.pdf

Dynamical Instability for Shearing Viscous Collapse

A model is proposed of a collapsing radiating star consisting of an isotropic fluid with shear viscosity undergoing radial heat flow with outgoing radiation. The pressure of the star, at the beginning of the collapse, is isotropic but owing to the presence of the shear viscosity the pressure becomes more and more anisotropic. The behaviour of the density, pressure, mass, luminosity and the effective adiabatic index is analysed. Our work is compared to the case of a collapsing shearing fluid of a previous model, for a star with 6 M⊙.

/pdf/radiating-gravitational-collapse-with-shear-viscosity-39o0ztce6x.pdf

Radiating gravitational collapse with shear viscosity

Les effets de l'ecoulement thermique sur l'instabilite dynamique pour un effondrement spherique non adiabatique sont etudies dans le modele considere par Herrera L., Le Denmat G. et Santos N.O. (1989). On montre que l'etendue instable du rapport Γ des chaleurs massiques est. (1) renforcee par la contribution due a la dissipation, dans la limite newtonienne; (2) renforcee par la correction relativiste due a la configuration de fond et diminuee par celle due a la dissipation, dans la limite post-newtonienne

/pdf/heat-flow-and-dynamical-instability-in-spherical-collapse-3pkdkqeaba.pdf

Heat flow and dynamical instability in spherical collapse

Dynamical models of prototype gravastars were constructed in order to study their stability. The models are the Visser–Wiltshire three-layer gravastars, in which an infinitely thin spherical shell of stiff fluid divides the whole spacetime into two regions, where the internal region is de Sitter, and the external one is Schwarzschild. It is found that in some cases the models represent the 'bounded excursion' stable gravastars, where the thin shell is oscillating between two finite radii, while in other cases they collapse until the formation of black holes occurs. In the phase space, the region for the 'bounded excursion' gravastars is very small in comparison to that of black holes, but not empty. Therefore, although the possibility of the existence of gravastars cannot be excluded from such dynamical models, our results indicate that, even if gravastars do indeed exist, that does not exclude the possibility of the existence of black holes.

https://iopscience.iop.org/article/10.1088/1475-7516/2008/06/025/pdf

R. Chan

Papers

Dynamical instability for radiating anisotropic collapse

Dynamical Instability for Shearing Viscous Collapse

Radiating gravitational collapse with shear viscosity

Heat flow and dynamical instability in spherical collapse

Bounded excursion stable gravastars and black holes