252 research outputs found
Accelerating expansion of the universe may be caused by inhomogeneities
No full textWe point out that, due to the nonlinearity of the Einstein equations, a homogeneous approximation in cosmology leads to the appearance of an additional term in the Friedmann equation. This new term is associated with the spatial inhomogeneities of the metric and can be expressed in terms of density fluctuations. Although it is not constant, it decays much slower (as t(-2/3)) than the other terms (like density) which decrease as t(-2). The presence of the new term leads to a correction in the scale factor that is proportional to t(2) and may give account of the recently observed accelerating expansion of the universe without introducing a cosmological constant
GW190521: a binary black hole merger with a total mass of 150 M⊙
No full textOn May 21, 2019 at 03:02:29 UTC Advanced LIGO and Advanced Virgo observed a short duration gravitational-wave signal, GW190521, with a three-detector network signal-to-noise ratio of 14.7, and an estimated false-alarm rate of 1 in 4900 yr using a search sensitive to generic transients. If GW190521 is from a quasicircular binary inspiral, then the detected signal is consistent with the merger of two black holes with masses of 85+21−14 M⊙ and 66+17−18 M⊙ (90% credible intervals). We infer that the primary black hole mass lies within the gap produced by (pulsational) pair-instability supernova processes, with only a 0.32% probability of being below 65 M⊙. We calculate the mass of the remnant to be 142+28−16 M⊙, which can be considered an intermediate mass black hole (IMBH). The luminosity distance of the source is 5.3+2.4−2.6 Gpc, corresponding to a redshift of 0.82+0.28−0.34. The inferred rate of mergers similar to GW190521 is 0.13+0.30−0.11 Gpc−3 yr−1
Site-selection criteria for the Einstein Telescope
No full textThe Einstein Telescope (ET) is a proposed next-generation, underground gravitational-wave detector to be based in Europe. It will provide about an order of magnitude sensitivity increase with respect to the currently operating detectors and, also extend the observation band targeting frequencies as low as 3 Hz. One of the first decisions that needs to be made is about the future ET site following an in-depth site characterization. Site evaluation and selection is a complicated process, which takes into account science, financial, political, and socio-economic criteria. In this paper, we provide an overview of the site-selection criteria for ET, provide a formalism to evaluate the direct impact of environmental noise on ET sensitivity, and outline the necessary elements of a site-characterization campaign
Publisher's Note: Search for gravitational waves from binary black hole inspiral, merger, and ringdown
No full textThis paper was published online on 6 June 2011 with an omission in the Collaboration author list. S. Dwyer has been
added as of 12 April 2012. The Collaboration author list is incorrect in the printed version of the journal
Accretion processes in magnetically and tidally perturbed Schwarzschild black holes
No full textWe study the accretion process in the region of the Preston-Poisson space-time describing a Schwarzschild black hole perturbed by an asymptotically uniform magnetic field and axisymmetric tidal structures. We find that the accretion disk shrinks and the marginally stable orbit shifts toward the black hole with the perturbation. The radiation intensity of the accretion disk increases, while the radius where radiation is maximal remains unchanged. The spectrum is blue-shifted. Finally, the conversion efficiency of accreting mass into radiation is decreased by both the magnetic and the tidal perturbations. © 2011 American Physical Society.published_or_final_versio
Search for subsolar-mass ultracompact binaries in advanced LIGO’s first observing run
No full textInternational audienceWe present the first Advanced LIGO and Advanced Virgo search for ultracompact binary systems with component masses between 0.2 M–1.0 M using data taken between September 12, 2015 and January 19, 2016. We find no viable gravitational wave candidates. Our null result constrains the coalescence rate of monochromatic (delta function) distributions of nonspinning (0.2 M, 0.2 M) ultracompact binaries to be less than 1.0×10 Gpc yr and the coalescence rate of a similar distribution of (1.0 M, 1.0 M) ultracompact binaries to be less than 1.9×10 Gpc yr (at 90% confidence). Neither black holes nor neutron stars are expected to form below ∼1 M through conventional stellar evolution, though it has been proposed that similarly low mass black holes could be formed primordially through density fluctuations in the early Universe and contribute to the dark matter density. The interpretation of our constraints in the primordial black hole dark matter paradigm is highly model dependent; however, under a particular primordial black hole binary formation scenario we constrain monochromatic primordial black hole populations of 0.2 M to be less than 33% of the total dark matter density and monochromatic populations of 1.0 M to be less than 5% of the dark matter density. The latter strengthens the presently placed bounds from microlensing surveys of massive compact halo objects (MACHOs) provided by the MACHO and EROS Collaborations
GW170104: Observation of a 50-Solar-Mass Binary Black Hole Coalescence at Redshift 0.2
No full textWe describe the observation of GW170104, a gravitational-wave signal produced by the coalescence of a pair of stellar-mass black holes. The signal was measured on January 4, 2017 at 10: 11: 58.6 UTC by the twin advanced detectors of the Laser Interferometer Gravitational-Wave Observatory during their second observing run, with a network signal-to-noise ratio of 13 and a false alarm rate less than 1 in 70 000 years. The inferred component black hole masses are 31.2(-6.0)(+8.4)M-circle dot and 19.4(-5.9)(+5.3)M(circle dot) (at the 90% credible level). The black hole spins are best constrained through measurement of the effective inspiral spin parameter, a mass-weighted combination of the spin components perpendicular to the orbital plane, chi(eff) =
-0.12(-0.30)(+0.21) . This result implies that spin configurations with both component spins positively aligned with the orbital angular momentum are disfavored. The source luminosity distance is 880(-390)(+450) Mpc corresponding to a redshift of z = 0.18(-0.07)(+0.08) . We constrain the magnitude of modifications to the gravitational-wave dispersion relation and perform null tests of general relativity. Assuming that gravitons are dispersed in vacuum like massive particles, we bound the graviton mass to m(g) <= 7.7 x 10(-23) eV/c(2). In all cases, we find that GW170104 is consistent with general relativity
Search for Subsolar-Mass Binaries in the First Half of Advanced LIGO's and Advanced Virgo's Third Observing Run
No full textWe report on a search for compact binary coalescences where at least one binary component has a mass between 0.2 M and 1.0 M in Advanced LIGO and Advanced Virgo data collected between 1 April 2019 1500 UTC and 1 October 2019 1500 UTC. We extend our previous analyses in two main ways: we include data from the Virgo detector and we allow for more unequal mass systems, with mass ratio q≥0.1. We do not report any gravitational-wave candidates. The most significant trigger has a false alarm rate of 0.14 yr-1. This implies an upper limit on the merger rate of subsolar binaries in the range [220-24200] Gpc-3 yr-1, depending on the chirp mass of the binary. We use this upper limit to derive astrophysical constraints on two phenomenological models that could produce subsolar-mass compact objects. One is an isotropic distribution of equal-mass primordial black holes. Using this model, we find that the fraction of dark matter in primordial black holes in the mass range 0.2 M<1.0 M is fPBHωPBH/ωDM6%. This improves existing constraints on primordial black hole abundance by a factor of ∼3. The other is a dissipative dark matter model, in which fermionic dark matter can collapse and form black holes. The upper limit on the fraction of dark matter black holes depends on the minimum mass of the black holes that can be formed: the most constraining result is obtained at Mmin=1 M, where fDBHωDBH/ωDM0.003%. These are the first constraints placed on dissipative dark models by subsolar-mass analyses
Search for intermediate mass black hole binaries in the first and second observing runs of the Advanced LIGO and Virgo network
No full textGravitational wave astronomy has been firmly established with the detection of gravitational waves from the merger of ten stellar mass binary black holes and a neutron star binary. This paper reports on the all-sky search for gravitational waves from intermediate mass black hole binaries in the first and second observing runs of the Advanced LIGO and Virgo network. The search uses three independent algorithms: two based on matched filtering of the data with waveform templates of gravitational wave signals from compact binaries, and a third, model-independent algorithm that employs no signal model for the incoming signal. No intermediate mass black hole binary event was detected in this search. Consequently, we place upper limits on the merger rate density for a family of intermediate mass black hole binaries. In particular, we choose sources with total masses M and mass ratios . For the first time, this calculation is done using numerical relativity waveforms (which include higher modes) as models of the real emitted signal. We place a most stringent upper limit of ~Gpcyr (in co-moving units at the 90% confidence level) for equal-mass binaries with individual masses M and dimensionless spins aligned with the orbital angular momentum of the binary. This improves by a factor of that reported after Advanced LIGO's first observing run
Characterization of the Virgo seismic environment
No full textThe Virgo gravitational wave detector is an interferometer (ITF) with 3 km arms located in Pisa, Italy. From July to October 2010, Virgo performed its third science run (VSR3) in coincidence with the LIGO detectors. Despite several techniques adopted to isolate the ITF from the environment, seismic noise remains an important issue for Virgo. Vibrations produced by the detector infrastructure (such as air conditioning units, water chillers/heaters, pumps) are found to affect Virgo's sensitivity, with the main coupling mechanisms being through beam jitter and scattered light processes. The Advanced Virgo design seeks to reduce ITF couplings to environmental noise by having most vibration-sensitive components suspended and in vacuum, as well as muffle and relocate loud machines. During the months of June and July in 2010, a Guralp-3TD seismometer was stationed at various locations around the Virgo site hosting major infrastructure machines. Seismic data were examined using spectral and coherence analysis with seismic probes close to the detector. The primary aim of this study was to identify noisy machines which seismically affect the ITF environment and thus require mitigation attention. Analyzed machines are located at various distances from the experimental halls, ranging from 10 to 100 m. An attempt is made to measure the attenuation of emitted noise at the ITF and correlate it with the distance from the source and with seismic attenuation models in soil
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