Two interesting news items with regards to the BH subject and recipient subject of the Nobel.......
https://www.ligo.org/news.php#:~:text=Now, scientists from LIGO and,the LIGO and Virgo detectors.
BEST CONSTRAINTS YET ON THE SIZE OF "MOUNTAINS" ON MILLISECOND PULSARS
29 Jul 2020 -- The LIGO and Virgo collaborations report the most stringent constraints yet on the size of deformations on millisecond pulsars in a
new paper submitted to the ArXiv. Based on our analysis, the strong gravity of these rapidly spinning neutron stars
constrains such deformations to be no bigger than the width of a human hair. While we have not detected gravitational-waves from millisecond pulsars, we have for the first time probed possible gravitational-wave emission mechanisms for these stars, and shown that only very small deformations would be necessary to produce observable gravitational waves.
the paper:
https://arxiv.org/abs/2007.14251
Gravitational-wave constraints on the equatorial ellipticity of millisecond pulsars
Abstract:
We present a search for continuous gravitational waves from five radio pulsars, comprising three recycled pulsars (PSR J0437-4715, PSR J0711-6830, and PSR J0737-3039A) and two young pulsars: the Crab pulsar (J0534+2200) and the Vela pulsar (J0835-4510). We use data from the third observing run of Advanced LIGO and Virgo combined with data from their first and second observing runs. For the first time we are able to match (for PSR J0437-4715) or surpass (for PSR J0711-6830) the indirect limits on gravitational-wave emission from recycled pulsars inferred from their observed spin-downs, and constrain their equatorial ellipticities to be less than 10−8. For each of the five pulsars, we perform targeted searches that assume a tight coupling between the gravitational-wave and electromagnetic signal phase evolution. We also present constraints on PSR J0711-6830, the Crab pulsar and the Vela pulsar from a search that relaxes this assumption, allowing the gravitational-wave signal to vary from the electromagnetic expectation within a narrow band of frequencies and frequency derivatives.
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and the most recent discovery.....
LIGO-VIRGO FINDS MYSTERY OBJECT IN THE 'MASS GAP'
23 Jun 2020 -- When the most massive stars die, they collapse under their own gravity and leave behind black holes; when stars that are a bit less massive die, they explode in supernovas and leave behind dense, dead remnants of stars called neutron stars. For decades, astronomers have been puzzled by a gap that lies between neutron stars and black holes: the heaviest known neutron star is no more than 2.5 times the mass of our sun, or 2.5 solar masses, and the lightest known black hole is about 5 solar masses. Now, scientists from LIGO and Virgo have announced the discovery of an object of 2.6 solar masses, placing it firmly in the mass gap. The object was found on August 14, 2019, as it merged with a black hole of 23 solar masses, generating gravitational waves that were detected by the LIGO and Virgo detectors.
For more details, read
the full press release and see
the GW190814 detection page.