Tag Archives: Laser Interferometer Gravitational-Wave Observatory

A Third Source of Gravitational Waves Appears to Have Been Detected

The US Laser Interferometer Gravitational-Wave Observatory (LIGO) began its third “observing run,” O3, on 1 April 2019 after a series of upgrades were completed on both LIGO instruments (in Hanford, Washington and Livingston, Louisiana) during an 18-month shutdown period after the second observing run, O2, ended on 25 August 2017.  The European Gravitational Observatory’s (EGO) Virgo instrument also joined O3.  Since its last observing run, which coincided with part of LIGO O2, Virgo also received a series of upgrades that have almost doubled its sensitivity.  O3 is scheduled to last for one calendar year.  Check out the details of these gravitational wave instruments and O3 at the following websites:

On 12 August, the LIGO / Virgo team reported:

“By July 31st, 2019, LIGO had sent out 25 alerts to possible detections, three have since been retracted, leaving us with 22 ‘candidate’ gravitational wave events. We call them “candidates” because we still need time to vet all of them. If all candidates are verified, then the number of detections made by LIGO in just the first third of O3 will double the number of detections made in its first two runs combined……So far, no electromagnetic counterparts related to our public alerts have been observed, but all candidates are being actively analyzed by LSC/Virgo science teams.”

As of July 31, 2019 LIGO/Virgo had seen:

  • 18 binary black hole merger candidates
  • 4 binary neutron star merger candidates

The LIGO-Virgo Collaboration has created the Gravitational Wave Candidate Event Database (GraceDB), which members of the public can access to track observations made during O3 here: 

https://gracedb.ligo.org/superevents/public/O3/

On 14 August 2019, the LIGO and Virgo instruments detected a gravitational wave event that appears to have come from a previously undetected source: the collision of a black hole and a neutron star.  This event, tentatively identified as S190814bv, is estimated to have occurred about 900 million light-years away.   Data from the three detectors enabled scientists to locate the source of these gravitational waves to a 23 square degree region of the sky, which would be about seven times the diameter of the Moon as seen from Earth.  While the gravitational wave signal was characterized as “remarkably strong,” so far, there have been no “multi-messenger” detections in the electromagnetic spectrum to help further refine the location and the nature of the event.

You’ll find a description of a black hole collision with a neutron star on the Simulating eXtreme Spacetimes (SXS) website at the following link:

https://www.black-holes.org/the-science-compact-objects/compact-objects/black-holes-and-neutron-stars

Here, SXS offers the following sequence of events for this exotic collision. 

Neutron star beginning to disrupt. The tidal forces of the black hole squeeze the star like a tube of toothpaste. The distance between the neutron star and the black hole is about 50 km, and they are orbiting hundreds of times per second. Source: SXS
Ejected tail flinging off into space. This matter will eventually contribute rare heavy elements to the interstellar medium. Source: SXS
Accretion disk swirling around the black hole. The accretion disk survives outside the black hole for less than a second. But this is enough time to release an enormous amount of energy in the form of neutrinos. It spans a little more than a hundred km from side to side.
Source: SXS

For more information, check the LIGO and Virgo websites for their news updates.

NSF and LIGO Team Announce First Detection of Gravitational Waves

Today, 11 February 2016, the National Science Foundation (NSF) and the Laser Interferometer Gravitational-Wave Observatory (LIGO) project team announced that the first detection of gravitational waves occurred on 14 September 2015. You can view a video of this announcement at the following link:

https://www.youtube.com/watch?v=_582rU6neLc

The first paper on this milestone event, “Observation of Gravitational Waves From a Binary Black Hole Merger,” is reported in Physical Review Letters, at the following link:

http://journals.aps.org/prl/pdf/10.1103/PhysRevLett.116.061102

The recorded signals from the two LIGO sites, Livingston, LA and Hanford, WA, are shown below, with the Hanford data time shifted to account for the slightly later arrival time of the gravitational wave signal at that detector location. The magnitude of the gravitational wave signal was characterized as being just below the detection threshold of LIGO before installation of the new advanced detectors, which improve LIGO sensitivity by a factor of 3 to 10.

LIGO signals

Source: NSF/LIGO

This milestone occurred during the engineering testing phase of the advanced LIGO detectors, before the start of their first official “observing run” on 18 September 2015.

Analysis and simulations conducted on the data indicate that the observed gravitational wave signals were generated when two orbiting black holes coalesced into a single black hole of smaller total mass and ejected about three solar masses of energy as gravitational waves.

In the Physical Review Letters paper, the authors provide the following diagram, which gives a physical interpretation of the observed gravitational wave signals.

Binary black holes merge

Note the very short timescale of this extraordinarily dynamic process. The recorded gravitational wave signals yielded an audible “chirp” when the two black holes merged.

With only two LIGO detectors, the source of the observed gravitational waves could not be localized, but the LIGO team reported that the source was in the southern sky, most likely in the vicinity of the Magellanic Clouds.

Localization of black hole merger Source: NSF/LIGO

The ability to localize gravitational wave signals will improve when additional gravitational wave detectors become operational later in this decade.

For more information on the current status of LIGO and other new-generation gravitational wave detectors, see my 16 December 2015 post: “100th Anniversary of Einstein’s Theory of General Relativity and the Advent of a New Generation of Gravity Wave Detectors.”

Update: 3 October 2017

 Congratulations to Rainer Weiss, Barry C. Barish, and Kip S. Thorne, all members of the LIGO / VIRGO Collaboration, for their award of the 2017 Nobel Prize in Physics for the first direct observation of gravitational waves. You can read the press release from the Royal Swedish Academy of Sciences here:

https://www.nobelprize.org/nobel_prizes/physics/laureates/2017/press.html

You also can read the scientific background on this award on the Royal Swedish Academy of Sciences website at the following link:

https://www.nobelprize.org/nobel_prizes/physics/laureates/2017/advanced-physicsprize2017.pdf