Largest yet Binary BH Collision Discovered:

[beecee]

https://phys.org/news/2018-12-scientists-biggest-black-hole-collision.html

Scientists detect biggest known black-hole collision

December 3, 2018, Australian National University

An international team of scientists have detected ripples in space and time, known as gravitational waves, from the biggest known black-hole collision that formed a new black hole about 80 times larger than the Sun – and from another three black-hole mergers.

The Australian National University (ANU) is playing a lead role in Australia's involvement with the gravitational wave discovery through a partnership in the Advanced Laser Interferometer Gravitational-wave Observatory (LIGO), which is based in the United States.

Professor Susan Scott, who is Leader of the General Relativity Theory and Data Analysis Group at ANU, said the team discovered the four collisions by re-analysing data from Advanced LIGO's first two observing runs.

extract:

The international research team has detected gravitational waves from 10 different black-hole mergers and one neutron star collision during the past three years. Neutron stars are the densest stars in the Universe, with a diameter of up to about 20 kilometres.

Read more at: https://phys.org/news/2018-12-scientists-biggest-black-hole-collision.html#jCp

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the paper:

https://arxiv.org/pdf/1811.12907.pdf
 

GWTC-1: A Gravitational-Wave Transient Catalog of Compact Binary Mergers Observed by LIGO and Virgo during the First and Second Observing Runs:

We present the results from three gravitational-wave searches for coalescing compact binaries with component masses above 1M during the first and second observing runs of the Advanced gravitational-wave detector network. During the first observing run (O1), from September 12th, 2015 to January 19th, 2016, gravitational waves from three binary black hole mergers were detected. The second observing run (O2), which ran from November 30th, 2016 to August 25th, 2017, saw the first detection of gravitational waves from a binary neutron star inspiral, in addition to the observation of gravitational waves from a total of seven binary black hole mergers, four of which we report here for the first time: GW170729, GW170809, GW170818 and GW170823. For all significant gravitational-wave events, we provide estimates of the source properties. The detected binary black holes have total masses between 18.6 +3.1 −0.7M and 85.1 +15.6 −10.9M, and range in distance between 320+120 −110 Mpc and 2750+1350 −1320 Mpc. No neutron star – black hole mergers were detected. In addition to highly significant gravitational-wave events, we also provide a list of marginal event candidates with an estimated false alarm rate less than 1 per 30 days. From these results over the first two observing runs, which include approximately one gravitational-wave detection per 15 days of data searched, we infer merger rates at the 90% confidence intervals of 110−3840 Gpc−3 y −1 for binary neutron stars and 9.7−101 Gpc−3 y −1 for binary black holes, and determine a neutron star – black hole merger rate 90% upper limit of 610 Gpc−3 y −1 .

VIII. CONCLUSIONS

We have reported the results from GW searches for compact mergers during the first and second observing runs by the Advanced GW detector network. Advanced LIGO and Advanced Virgo have confidently detected gravitational waves from ten stellar-mass binary black hole mergers and one binary neutron star inspiral. The signals were discovered using three independent analyses: two matched-filter searches [8, 9] and one weakly modeled burst search [11]. We have reported four previously unpublished BBH signals discovered during O2, as well as updated FARs and parameter estimates for all previously reported GW detections. The reanalysis of O1 data did not reveal any new GW events, but improvements to the various detection pipelines have resulted in an increase of the significance of GW151012. Including these four new BBH mergers, the observed BBHs span a wide range of component masses, from 7.7 +2.2 −2.6 M to 50.6 +16.6 −10.2 M. One of the new events, GW170729, is found to be the highestmass BBH observed to date, with GW170608 still being the lightest BBH [16]. Similar to previous results, we find that the spins of the individual black holes are only weakly constrained, though for GW151226 and also for GW170729 we find that χeff is positive and thus can rule out two non-spinning black holes as their constituents at greater than the 90% credible level. The binary mergers observed during O1 and O2 range in distance between 40+10 −10 Mpc for the binary neutron star inspiral GW170817 to 2750+1350 −1320 Mpc for GW170729, making it not only the heaviest BBH but also the most distant one observed to date. For the BNS merger, GW170817, we have presented conservative upper limits on the properties of the remnant. The three other new events GW170809, GW170818, and GW170823 are all identified as heavy stellarmass BBH mergers, ranging in total mass from 59.2 +5.4 −3.9M to 68.9 +9.9 −7.1M. GW170818 is the second triple-coincident LIGO-Virgo GW event and is localized to an area of 39 deg2 , making it the best localised BBH to date. A similar impact of Virgo on the sky localization was already seen for GW170814 [15], reaffirming the importance of a global GW detector network for accurately localizing GW sources [188]. We have also presented a set of 14 marginal candidate events identified by the two matched-filter searches. The number of observed marginal events is consistent with our expectation given the chosen FAR threshold, but it is not possible to say whether or not a particular marginal trigger is a real GW signal. The properties of the observations reported in this catalog are based on general relativistic waveform models. Tests of the consistency of these observations with GR can be found in Refs. [14, 201, 202]. Even with the set of ten BBH and one BNS, several outstanding questions remain regarding the origin and evolution of the detected binaries. To date, no binary components have been observed in either of the two putative mass gaps [132, 133] – one between NSs and BHs and the other one due to pair instability supernovae [130, 203]. Perhaps more intriguingly, the component spins, when measurable, tend to favor small magnitudes – contrasting with the sample of Galactic X-ray binaries [204], which have a spread encompassing the entire range of allowed values. This observation, however, comes with the caveat that spin magnitudes could be relatively large, but tilted into the orbital plane. The latter favors a formation scenario where no spin alignment process is present, e.g., assembly in globular clusters [163, 165]. Several studies [157–160, 205–210] indicate that with a few hundred detections, more detailed formation scenarios and evolutionary details can be parsed from the population. The BBH sample from O1 and O2 allows for new constraints on the primary mass power law index α = 0.4 +1.3 −1.9 [54]. The third observing run (O3) of Advanced LIGO and Virgo is planned to commence in early 2019. The inferred rate of BBH mergers is 9.7−101 Gpc−3 y −1 and for BNS 110−3840 Gpc−3 y −1 , for NSBH binaries we obtain an improved 90% upper limit of the merger rate of 610 Gpc−3 y −1 ; in combination with further sensitivity upgrades to both LIGO and Virgo as well as the prospects of the Japanese GW detector KAGRA [211–213] joining the network possibly towards the end of O3 in 2019, many tens of binary observations are anticipated in the coming years [188].

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OK, again good news.

My question/s concerns what was the result of the binary NS merger....it says "It could have been a neutron star that collapsed to a black hole after some time or turned immediately into a black hole,"  So why would there have been any delay before collapsing to BH status? I would imagine once the Schwarzchild radius is reached, then a BH is formed, and after settling down after the merger, wouldn't that have been immediate?

And of course an amazing turn of events with more GW's resulting from more collisions in past runs after further research...Amazing stuff!

 

[beecee]

And why were not these extra "events" discovered by aLIGO/VIRGO research scientists themselves? Were they actually over cautious in there announcements? Does no one else see this as momentous and important?

https://australiascience.tv/gravitational-waves-biggest-black-hole-merger-ever-detected-revealed/

"All four newly confirmed black hole mergers were found in archived observing runs from 2017, coming to light as a result of routine data-cleaning".

"They bring the total number of mergers detected to 10 – plus a single neutron star–neutron star collision – over the past three years"

And I'm rather disappointed that the announcement by the aLIGO VIRGO media people, have not seen fit to give credit to the great work as achieved by the Aussie contingent and the Australian National University (ANU) here......

https://www.ligo.caltech.edu/news

news release:

LIGO and Virgo announce four new Gravitational Wave detections:

The National Science Foundation's LIGO, and the European based Virgo, have published new results from the first two observing runs. Four new BH mergers are newly announced...more at link 

[Strange]

On 03/12/2018 at 8:09 PM, beecee said:

My question/s concerns what was the result of the binary NS merger....it says "It could have been a neutron star that collapsed to a black hole after some time or turned immediately into a black hole,"  So why would there have been any delay before collapsing to BH status? I would imagine once the Schwarzchild radius is reached, then a BH is formed, and after settling down after the merger, wouldn't that have been immediate?

I'm not sure. But neutron stars have quite complex structure. It could be that if it is close to the threshold mass, it takes some time for the system to "settle down" and collapse to sufficient density for the mass to be within the Schwarzschild radius.

 

13 hours ago, beecee said:

And why were not these extra "events" discovered by aLIGO/VIRGO research scientists themselves?

I guess because the second team had more time to use extra methods to clean up and extract information from the data.

And, because this is a large collaboration, I assume these scientists are counted as part of the LIGO team.

13 hours ago, beecee said:

And I'm rather disappointed that the announcement by the aLIGO VIRGO media people, have not seen fit to give credit to the great work as achieved by the Aussie contingent and the Australian National University (ANU) here......

Maybe they should. But the original papers had something like three or more pages just listing the authors. More recent ones seem to be credited to "the Logo collaboration" or similar to get over that problem.