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Title: Weighing The Black Holes Of GW150914
Author: Yuan K. Ha

We evaluate the mass of the black holes of GW150914 at their event horizons via quasi-local energy approach and obtain the values of 70 and 55 solar masses, compared to their asymptotic values of 36 and 29 units, respectively, as reported by LIGO. A higher mass at the event horizon is compulsory in order to overcome the huge negative gravitational potential energy surrounding the black holes and allow for the emission of gravitational waves. We estimate the initial mass of the stars which collapsed to form the black holes from the horizon mass and obtain the impressive values of 93 and 73 solar masses for these progenitor stars.

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Title: GW170104: Observation of a 50-Solar-Mass Binary Black Hole Coalescence at Redshift 0.2
Author: The LIGO Scientific Collaboration, the Virgo Collaboration: B. P. Abbott, R. Abbott, T. D. Abbott, F. Acernese, K. Ackley, C. Adams, T. Adams, P. Addesso, R. X. Adhikari, V. B. Adya, C. Affeldt, M. Afrough, B. Agarwal, M. Agathos, K. Agatsuma, N. Aggarwal, O. D. Aguiar, L. Aiello, A. Ain, P. Ajith, B. Allen, G. Allen, A. Allocca, P. A. Altin, A. Amato, A. Ananyeva, S. B. Anderson, W. G. Anderson, S. Antier, S. Appert, K. Arai, M. C. Araya, J. S. Areeda, N. Arnaud, K. G. Arun, S. Ascenzi, G. Ashton, M. Ast, S. M. Aston, P. Astone, P. Aufmuth, C. Aulbert, K. AultONeal, A. Avila-Alvarez, S. Babak, P. Bacon, M. K. M. Bader, S. Bae, P. T. Baker, F. Baldaccini, G. Ballardin, S. W. Ballmer, S. Banagiri, J. C. Barayoga, S. E. Barclay, B. C. Barish, D. Barker, F. Barone, B. Barr, L. Barsotti, M. Barsuglia, et al. (988 additional authors not shown)

We 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^{+8.4}_{-6.0} solar masses and 19.4^{+5.3}_{-5.9} solar masses (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^{+0.21}_{-0.30}. 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^{+450}_{-390} Mpc corresponding to a redshift of z={+0.08}_{-0.07}. 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/cē. In all cases, we find that GW170104 is consistent with general relativity.

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Title: Fermi observations of the LIGO event GW170104
Author: On behalf of the Fermi-GBM, Fermi-LAT collaborations

We present the Fermi Gamma-ray Burst Monitor (GBM) and Large Area Telescope (LAT) observations of the LIGO binary black hole merger (BBH) event GW170104. No candidate electromagnetic counterparts was detected by either GBM or LAT. A detailed analysis of the GBM and LAT data over timescales from seconds to days covering the LIGO localization region is presented. The resulting flux upper bound from the GBM is (5.2--9.4) x 10^-7 erg cm^-2 s^-1 in the 10-1000 keV range and from the LAT is (0.2--13) x 10^-9 erg cm^-2 s^-1 in the 0.1--1 GeV range. We also describe the improvements to our automated pipelines and analysis techniques for searching for and characterizing the potential electromagnetic counterparts for future gravitational wave events from Advanced LIGO/VIRGO.

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Third gravitational wave detection puts new spin on black holes

The discovery, reported today in the journal Physical Review Letters, has important implications for our understanding of black holes, dark matter and the early Universe. It was made on January 4 this year, when an international research team picked up the infinitesimal wobble produced by two black holes, 3 billion light-years away. They spiralled towards each other and eventually merged to form a bigger black hole 50 times the mass of the Sun.
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Third gravitational waves discovery 'opens new window on Universe'

The black hole that was formed has a mass 49 times that of the sun. Before the groundbreaking first detection of gravitational waves in 2015 - caused by the formation of a black hole with a solar mass of 62 - scientists were unaware of the existence of black holes larger than 20 solar masses.
This is the third such signal to have been found by the scientists working with LIGO data, which confirms a key prediction of Albert Einstein's 1915 general theory of relativity.

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Simulation of GW170104

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LIGO detects merging black holes for third time

The collision of a pair of colossal, stellar-mass black holes has made itself heard, nearly 3 billion light years away, through a cosmic microphone on Earth.
On Jan. 4, the Laser Interferometry Gravitational-wave Observatory (LIGO) picked up a barely perceptible signal that scientists quickly determined to be a gravitational wave - a ripple of energy passing through the curvature of spacetime. The event, published today in Physical Review Letters, marks the third direct detection of a gravitational wave.

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GW170104 was a gravitational wave signal detected by the LIGO observatory on 4 January 2017. On 1 June 2017, the LIGO and Virgo collaborations announced that they had reliably verified the signal, making it the third such signal, after GW150914 and GW151226.
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