SATLASGravitational waves · Ground
LIGO
Laser Interferometer Gravitational-Wave Observatory
OperatingOperating since 14 September 2015.
The fourth observing run (O4) ended on 18 November 2025. A six-month intermediate run (IR1), at about O4 sensitivity, is expected to start in mid-January 2027. O5 is in early planning, conceived as spanning 2029–2031.
Two 4 km dual-recycled Michelson interferometersinterferometryCombining waves from separate receivers coherently. In radio and optical astronomy, correlating signals from separated telescopes gives the resolution of one as large as their separation. In gravitational-wave detection, a laser Michelson interferometer measures tiny differential changes in its arm lengths. with Fabry–Pérot arm cavities and squeezed light, at Hanford and Livingston, with strainstrainThe fractional change in length, ΔL/L, a passing gravitational wave induces; the calibrated output of a detector. Signals from merging black holes reach about 10⁻²¹, a change of a few × 10⁻¹⁸ m over a 4 km arm. noise below 10⁻²³ /√Hz around 100 Hz across a 10 Hz–5 kHz band. First detection, GW150914, in 2015; with Virgo and KAGRA, hundreds of compact binary coalescencescompact binary coalescenceThe inspiral and merger of two black holes, two neutron stars or one of each. The signal sweeps up in frequency and amplitude (a chirp) until the objects merge; its shape gives their masses, spins and distance. since, including the binary neutron starneutron starThe collapsed core of a massive star: about 1.4 solar masses in a 12 km radius, at above nuclear density. Its mass–radius relation tests the equation of state of dense matter. GW170817. Each detector reached a binary-neutron-star range of 150–160 MpcparsecThe distance at which 1 AU subtends 1″: 3.086 × 10¹⁶ m, or 3.26 light years. Galaxies are measured in Mpc. in O4observing runA planned period of coordinated LIGO–Virgo–KAGRA data taking (O1 in 2015, O4 in 2023–2025), separated by breaks for detector upgrades..
- Operator
- NSF, Caltech, MIT
- Site
- Hanford, Washington and Livingston, Louisiana
- Aperture
- Two 4 km laser interferometers
- Frequency band
- 10 Hz – 5 kHz
- Messenger
- Gravitational waves
- First detection
- 14 September 2015
Frequency band
Gravitational-wave frequency, from pulsar timing arrays (nHz) through space interferometers (mHz) to ground-based detectors (kHz).
Sky coverage
Nearly omnidirectional, so it monitors most of the sky at once but localises poorly. Two detectors give arcs of hundreds to thousands of deg²square degreeUnit of solid angle: one degree by one degree on the sky. The whole sky is about 41,253 deg²; the full Moon covers about 0.2 deg². at 90% credibility; Virgo and KAGRA triangulate loud events down to tens of deg².
Loading HiPS tiles…
Data products
Each detector records hundreds of thousands of channels. CalibrationcalibrationRemoving instrument signatures and putting data in physical units: subtracting bias and dark current, dividing by the flat field (pixel-to-pixel sensitivity), correcting non-linearity and fitting the astrometric solution. Reference files hold these calibrations and are updated as the instrument is understood. reduces them to one time series per detector, the strain h(t), sampled at 16 kHz. Low-latency search pipelines scan it in real time and issue public alertsalertA machine-readable notice that a source has appeared, changed or been detected, issued within seconds to days so other facilities can follow up. Optical alerts reach users through brokers; high-energy, neutrino and gravitational-wave alerts through GCN. within minutes; months later, offline searches and parameter estimationparameter estimationBayesian inference of a signal's source properties by comparing waveform models with the strain data. The result is a set of posterior samples that encodes uncertainties and correlations between parameters. produce the catalogue of confirmed events. Strain for whole observing runs is released in blocks after the collaboration's proprietary periodexclusive access periodThe time, often 12 months, during which only the proposing team can use new data before they become public in the archive. Survey and community missions increasingly have none..
Where to start
1Masses, distances and sky positions of known events
2Redoing inference or population studies
3Searching for counterparts in real time
From detector to catalogueAbout data levels
| 1RawDetector channels | 2CalibratedStrain h(t) | 3MeasuredParameter estimation | 4CombinedCatalogues | |
|---|---|---|---|---|
| Archive products | ||||
| Low latency | Searched as calibrated data arrive, ahead of the archive products Superevents and sky maps3Multi-order HEALPix FITS, JSON via GCN Kafka | |||
Starting point, listed aboveContributed: made outside the mission pipelineSelect a product for its full entry
All products
RawDetector channels
Raw and auxiliary channels
GWF frame files
Not public
The interferometer's error signals plus environmental monitors (seismometers, magnetometers, microphones).
CalibratedStrain h(t)
Event strain
HDF5, GWF, text
Calibrated strain around each catalogued event, at 4 kHz and 16 kHz sampling, released with the catalogue.
Bulk observing-run strain
HDF5, GWF
Public access: Yes, after a proprietary period (O4a was released with GWTC-4.0 in 2025)
Continuous strain for whole runs, released in blocks after a proprietary period, with data-quality flags.
MeasuredParameter estimation
Parameter-estimation samples
HDF5
Posterior samples for every event, for anyone who wants to redo population studies.
CombinedCatalogues
Gravitational-Wave Transient Catalogs (GWTC)
Catalogue
Confirmed events with masses, spins, distances and sky positions; GWTC-4.0 covers the first part of O4.
AlertsLow-latency alerts
Superevents and sky maps
Multi-order HEALPix FITS, JSON via GCN Kafka
Candidate mergers with false-alarm ratefalse-alarm rateHow often detector noise alone would produce a candidate at least as significant, e.g. once per 100 years. The main significance statistic for gravitational-wave alerts., source class and a probability sky mapsky localisationWhere on the sky a source probably lies, published as a HEALPix probability map; its size is quoted as the area containing 90% probability. Two detectors give long arcs of hundreds to thousands of deg²; a third and fourth detector shrink it by triangulation., sent within minutes so telescopes can look for light.
Archives
Quick start
gwpy fetches open strain data from GWOSC.
from gwosc.datasets import event_gps
from gwpy.timeseries import TimeSeries
gps = event_gps("GW150914")
strain = TimeSeries.fetch_open_data("H1", gps - 16, gps + 16)
strain.whiten().bandpass(30, 400).plot()Key papers
Instrument · 2015
Advanced LIGO (opens in a new tab)LIGO Scientific Collaboration, Aasi et al., CQG 32, 074001
The design of the Advanced LIGO detectors: optics, seismic isolation, lasers and the interferometer configuration.
Instrument · 2025
Advanced LIGO detector performance in the fourth observing run (opens in a new tab)Capote et al., PRD 111, 062002
The O4 upgrades, including frequency-dependent squeezing, and the resulting sensitivity of both detectors.
Pipeline · 2020
A guide to LIGO–Virgo detector noise and extraction of transient gravitational-wave signals (opens in a new tab)LIGO and Virgo Collaborations, Abbott et al., CQG 37, 055002
Detector noise, glitches and the search and parameter-estimation methods, written for people using GWOSC strain data.
Data · 2026
GWTC-4.0: Updating the Gravitational-wave Transient Catalog with Observations from the First Part of the Fourth LIGO–Virgo–KAGRA Observing Run (opens in a new tab)LIGO, Virgo and KAGRA Collaborations, Abac et al., ApJL 1004, L22
128 new candidates from O4a, with source properties for 86 of them.
Data · 2023
GWTC-3: Compact Binary Coalescences Observed by LIGO and Virgo during the Second Part of the Third Observing Run (opens in a new tab)LIGO, Virgo and KAGRA Collaborations, Abbott et al., PRX 13, 041039
Data · 2023
Open Data from the Third Observing Run of LIGO, Virgo, KAGRA, and GEO (opens in a new tab)LIGO, Virgo and KAGRA Collaborations, Abbott et al., ApJS 267, 29
What the O3 strain release on GWOSC contains, its data-quality flags and how to use it.
Data · 2021
Open data from the first and second observing runs of Advanced LIGO and Advanced Virgo (opens in a new tab)LIGO and Virgo Collaborations, Abbott et al., SoftwareX 13, 100658
Result · 2016
Observation of Gravitational Waves from a Binary Black Hole Merger (opens in a new tab)LIGO and Virgo Collaborations, Abbott et al., PRL 116, 061102
GW150914, the first direct detection.
Result · 2017
GW170817: Observation of Gravitational Waves from a Binary Neutron Star Inspiral (opens in a new tab)LIGO and Virgo Collaborations, Abbott et al., PRL 119, 161101
Result · 2017
Multi-messenger Observations of a Binary Neutron Star Merger (opens in a new tab)LIGO, Virgo and partner collaborations, Abbott et al., ApJL 848, L12
GW170817 with GRB 170817A and the kilonova in NGC 4993, across the electromagnetic spectrum.
Science cases
Sources
Verified 15 November 2026.
- LIGO Caltech (opens in a new tab)
- LIGO-Virgo-KAGRA observing plans (opens in a new tab)
- O4 completion announcement (opens in a new tab)
- IGWN observing capabilities (opens in a new tab)
- AEI gravitational-wave astronomy (opens in a new tab)
- GW150914 detection paper (opens in a new tab)
- LIGO detector performance in O4 (Capote et al. 2025) (opens in a new tab)
Other gravitational waves facilities: NANOGrav, Virgo, KAGRA, LISA