tuco wrote:The Universe Probably 'Remembers' Every Single Gravitational Wave - https://www.livescience.com/65441-gravi ... emory.html

Persistent gravitational wave observables: General framework - https://journals.aps.org/prd/abstract/1 ... .99.084044

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Sounds cool but what does it mean for astro/physics? Could this be used for anything else but "history of gravitational waves" field?

Estimated false alarm rate for #S190728q is once every million billion years, so this looks like a very strong candidate for a real #GravitationalWaves event - our 22nd since our 3rd observing run began on April 1st. You can find a full list at https://gracedb.ligo.org/superevents/public/O3/

Abstract

We report the observation of a compact binary coalescence involving a 22.2–24.3 Msolar black hole and a compact
object with a mass of 2.50–2.67 Msolar (all measurements quoted at the 90% credible level). The gravitational-wave signal, GW190814, was observed during LIGO’s and Virgo’s third observing run on 2019 August 14 at
21:10:39 UTC and has a signal-to-noise ratio of 25 in the three-detector network. The source was localized to 18.5 deg2 at a distance of 241+41-45 Mpc; no electromagnetic counterpart has been confirmed to date. The source has the most unequal mass ratio yet measured with gravitational waves, 0.112+0.008-0.009, and its secondary component is either the lightest black hole or the heaviest neutron star ever discovered in a double compact-object system. The dimensionless spin of the primary black hole is tightly constrained to „0.07. Tests of general relativity reveal no measurable deviations from the theory, and its prediction of higher-multipole emission is confirmed at high confidence. We estimate a merger rate density of 1–23 Gpc−3 yr−1 for the new class of binary coalescence sources that GW190814 represents. Astrophysical models predict that binaries with mass ratios similar to this event can form through several channels, but are unlikely to have formed in globular clusters. However, the combination of mass ratio, component masses, and the inferred merger rate for this event challenges all current models of the formation and mass distribution of compact-object binaries.

Ironclad wrote:'Black neutron star' discovery changes astronomy https://www.bbc.co.uk/news/science-environment-53151106
Bit more

JUNE 25, 2020
Black Hole Collision May Have Exploded With Light

When two black holes spiral around each other and ultimately collide, they send out gravitational waves - ripples in space and time that can be detected with extremely sensitive instruments on Earth. Since black holes and black hole mergers are completely dark, these events are invisible to telescopes and other light-detecting instruments used by astronomers. However, theorists have come up with ideas about how a black hole merger could produce a light signal by causing nearby material to radiate.

Now, scientists using Caltech's Zwicky Transient Facility (ZTF) located at Palomar Observatory near San Diego may have spotted what could be just such a scenario. If confirmed, it would be the first known light flare from a pair of colliding black holes.

The merger was identified on May 21, 2019, by two gravitational wave detectors - the National Science Foundation's Laser Interferometer Gravitational-wave Observatory (LIGO) and the European Virgo detector - in an event called GW190521g. That detection allowed the ZTF scientists to look for light signals from the location where the gravitational wave signal originated. These gravitational wave detectors have also spotted mergers between dense cosmic objects called neutron stars, and astronomers have identified light emissions from those collisions.

The ZTF results are described in a new study published in the journal Physical Review Letters. The authors hypothesize that the two partner black holes, each several dozen times more massive than the Sun, were orbiting a third, supermassive black hole that is millions of times the mass of the Sun and surrounded by a disk of gas and other material. When the two smaller black holes merged, they formed a new, larger black hole that would have experienced a kick and shot off in a random direction. According to the new study, it may have plowed through the disk of gas, causing it to light up.

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