List of gravitational wave observations

This is a list of observed/candidate gravitational wave events. Direct observation of gravitational waves, which commenced with the detection of an event by LIGO in 2015, constitutes part of gravitational wave astronomy. LIGO has played a role in all subsequent detections to date, with Virgo joining in August 2017.

Nomenclature and timeline

Gravitational wave events are named starting with the prefix GW, while observations that trigger an event alert but have not (yet) been confirmed are named starting with the prefix S. Six digits then indicate the final two digits of the year the event was observed, two digits for the month and two digits for the day of observation. This is similar to the systematic naming for other kinds of astronomical event observations, such as those of gamma-ray bursts. Probable detections that are not confidently identified as gravitational wave events are designated LVT ("LIGO-Virgo trigger"). Known gravitational wave events come from the merger of two black holes (BH), two neutron stars (NS), or a black hole and a neutron star (BHNS). Some objects are in the mass gap between the largest predicted neutron star masses ( Tolman–Oppenheimer–Volkoff limit) and the smallest known black holes.

Observations are made in "runs", three of them so far, with maintenance and upgrades of the detectors made between runs. The first run, O1, ran from 12 September 2015 to 19 January 2016, with O2 from 30 November 2016 to 25 August 2017. O3 began on 1 April 2019; it is divided into O3a, from 1 April to 30 September 2019, and O3b, from 1 November 2019 to 27 March 2020. Suspension of observation during October 2019 was for instrument upgrades and fixes, and cessation in March 2020 was due to the COVID-19 pandemic. The fourth run, O4, is planned (as of June 2022) to begin in March 2023.

List of gravitational wave events

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, BGCOLOR="#fff0f0", GW150914
09:50:45
, , 2016-02-11
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, style="background:#888888; text-align:center;", BH

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, style="background:#888888; text-align:center;", BH

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, , First GW detection;
first BH merger observed
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, BGCOLOR="#fff0f0",
09:54:43
, , 2016-06-15
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, , Formerly candidate LVT151012;
accepted as astrophysical since February 2019
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, BGCOLOR="#fff0f0", GW151226
03:38:53
, , 2016-06-15
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, BGCOLOR="#fffff0", GW170104
10:11:58
, , 2017-06-01
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, BGCOLOR="#fffff0", GW170608
02:01:16
, , 2017-11-16
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, , Smallest BH progenitor
masses to date
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, BGCOLOR="#fffff0", GW170729
18:56:29
, , 2018-11-30
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, , Largest progenitor masses until GW190521
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, BGCOLOR="#fffff0", GW170809
08:28:21
, , 2018-11-30
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, BGCOLOR="#fffff0", GW170814
10:30:43
, , 2017-09-27
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, , First announced detection by
three observatories; first polarization measurement
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*
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, BGCOLOR="#fffff0", GW170817
12:41:04
, , 2017-10-16
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, style="background:#AADDDD; text-align:center;", NS

, style="text-align:center;", ≤ 2.8
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, , First NS merger observed in
GW; first detection of EM counterpart ( GRB 170817A; AT 2017gfo); nearest event to date
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, BGCOLOR="#fffff0", GW170818
02:25:09
, , 2018-11-30
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, BGCOLOR="#fffff0", GW170823
13:13:58
, , 2018-11-30
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, BGCOLOR="#f0fff0", GW190408_181802
2019-04-08
, , 2020-10-27
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, BGCOLOR="#f0fff0", GW190412
2019-04-12
05:30:44
, , 2020-04-17
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, , First possible observation of a merger of two black holes of very different masses
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, BGCOLOR="#f0fff0", GW190413_052954
2019-04-13
, , 2020-10-27
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, BGCOLOR="#f0fff0", GW190413_134308
2019-04-13
, , 2020-10-27
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, BGCOLOR="#f0fff0", GW190421_213856
2019-04-21
, , 2020-10-27
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, BGCOLOR="#f0fff0", GW190424_180648
2019-04-21
, , 2020-10-27
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, BGCOLOR="#f0fff0", GW190425
2019-04-25
08:18:05
, , 2020-01-06
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, , Originally designated S190425z (z:26th trigger, UTC day), this trigger was detected by a single LIGO instrument (of three LVC stations), and is considered by some scientists to have been confirmed as a binary neutron star merger.

It was published in 2020 that a gamma-ray burst was detected ( GRB 190425) ~0.5 seconds after the LIGO trigger, lasting 6 seconds and bearing similarities to GRB170817 (such as weakness ost_power_in_sub-100_keV,_or_soft_X-rays)_bands.html" ;"title="X-rays.html" ;"title="ost power in sub-100 keV, or soft X-rays">ost power in sub-100 keV, or soft X-rays) bands">X-rays.html" ;"title="ost power in sub-100 keV, or soft X-rays">ost power in sub-100 keV, or soft X-rays) bands elevated energetic photon background levels [signal exceeding background by less than a factor of 2], and similar differences from other transients classified as short GRBs). Confidence was established for interpretation of a set of peaks through a control interval of only 2 days prior to the LIGO-Livingston trigger in INTEGRAL Electronic anticoincidence, could not be corroborated by other instruments and wasn't initially noted as a significant event. Non-detection in other instruments may be a consequence of an Earth-occulted source as the Fermi telescope attempted follow-up.
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, BGCOLOR="#f0fff0", GW190521
2019-05-21
03:02:29
, , 2020-09-02
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, , Originally designated S190521g. Largest progenitor masses to date.
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, BGCOLOR="#f0fff0", GW190814 2019-08-14 21:11:18
, , 2020-06-23
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, , No optical counterpart was discovered despite an extensive search of the probability region. The mass of the lighter component is estimated to be 2.6 times the mass of the Sun, placing it in the mass gap between neutron stars and black holes.
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, BGCOLOR="#f0f0ff", GW200105
2020-01-05 16:24:26
, , 2021-06-29
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, , First event confirmed to be a black hole and neutron star merger. Originally designated S200105ae.
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, BGCOLOR="#f0f0ff", GW200115
2020-01-15 04:23:09
, , 2021-06-29
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, , Second event confirmed to be a black hole and neutron star merger. Originally designated S200115j.
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Candidate events and marginal detections

Marginal detections from O1 and O2

In addition to well-constrained detections listed above, a number of low-significance detections of possible signals were made by LIGO and Virgo. Their characteristics are listed below:

Observation candidates from O3/2019

From observation run O3/2019 on, observations are published as Open Public Alerts to facilitate multi-messenger observations of events. Candidate event records can be directly accessed at the Gravitational-Wave Candidate Event Database (GraceDB). On 1 April 2019, the start of the third observation run was announced with a circular published in the public alerts tracker. The first O3/2019 binary black hole detection alert was broadcast on 8 April 2019. A significant percentage of O3 candidate events detected by LIGO are accompanied by corresponding triggers at Virgo. False alarm rates are mixed, with more than half of events assigned false alarm rates greater than 1 per 20 years, contingent on presence of glitches around signal, foreground electromagnetic instability, seismic activity, and operational status of any one of the three LIGO-Virgo instruments. For instance, events S190421ar and S190425z weren't detected by Virgo and LIGO's Hanford site, respectively.

The LIGO/Virgo collaboration took a short break from observing during the month of October 2019 to improve performance and prepare for future plans, with no signals detected in that month as a result.

The Kamioka Gravitational Wave Detector ( KAGRA) in Japan became operational on 25 February 2020, likely improving the detection and localization of future gravitational wave signals. However, KAGRA does not report their signals in real-time on GraceDB as LIGO and Virgo do, so the results of their observation run will likely not be published until the end of O3.

The LIGO-Virgo collaboration ended the O3 run early on March 27, 2020 due to health concerns from the COVID-19 pandemic. On 15 June 2022, LIGO announced to start the O4 observing run in March 2023.

See also

* GRB 150101B, a weak gamma-ray burst trigger observed prior to aLIGO O1 (beginning September 12, 2015), with claimed similarities to model-supported possible neutron star merger GW170817/GRB 170817A/ AT2017gfo.

Notes

References

External links

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{{Portal bar, Physics, Astronomy, Stars, Spaceflight, Outer space, Solar System

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