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astronomy

LIGO

LIGO is a astronomy topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand LIGO rather than just read about it. In short: The Laser Interferometer Gravitational-Wave Observatory (LIGO) is a large-scale physics experiment and observatory designed to detect cosmic gravitational waves. Prior to LIGO, all data about the universe had come in the form of light and other forms of electromagnetic radiation, from limited direct exploration on relatively nearby Solar System objects such as the Moon, Mars, Venus, Jupiter and their moons, asteroid…

LIGO — main illustration
LIGO — illustration

Key takeaways

  • LIGO belongs to astronomy; place it in that map before memorising details.
  • Learn the definition first, then one example that makes the definition concrete.
  • Connect LIGO to a quantity you can measure, compute or draw — that is where exam questions come from.
  • Reproduce the core statement of LIGO from memory before moving on to harder problems.

Reference excerpt

The Laser Interferometer Gravitational-Wave Observatory (LIGO) is a large-scale physics experiment and observatory designed to detect cosmic gravitational waves. Prior to LIGO, all data about the universe had come in the form of light and other forms of electromagnetic radiation, from limited direct exploration on relatively nearby Solar System objects such as the Moon, Mars, Venus, Jupiter and their moons, asteroids etc., and from high energy cosmic particles. Initially, two large observatories were built in the United States with the aim of detecting gravitational waves by laser interferometry. Two additional, smaller gravitational wave observatories are now operational: one in Japan (KAGRA), and one in Italy (Virgo). The two LIGO observatories use mirrors spaced 4 kilometres (13,000 ft) apart to measure changes in length—over an effective span of 1,120 kilometres (700 mi)—of less than one ten-thousandth the charge diameter of a proton. The initial LIGO observatories were funded by the United States National Science Foundation (NSF). They were conceived, built, and are operated by Caltech and MIT. They collected data from 2002 to 2010, but no gravitational waves were detected during that period. The Advanced LIGO Project to enhance the original LIGO detectors began in 2008, and continues to be supported by the NSF, with important contributions from the United Kingdom's Science and Technology Facilities Council, the Max Planck Society of Germany, and the Australian Research Council. The improved detectors began operation in 2015. The detection of gravitational waves was reported in 2016 by the LIGO Scientific Collaboration (LSC) and the Virgo Collaboration with the international participation of scientists from several universities and research institutions. Scientists involved in the project and the analysis of the data for gravitational-wave astronomy are organized by the LSC, which includes more than 1,000 scientists worldwide, as well as 440,000 active Einstein@Home users as of December 2016. LIGO is the largest and most ambitious project ever funded by the NSF. In 2017, the Nobel Prize in Physics was awarded to Rainer Weiss, Kip Thorne and Barry Barish "for decisive contributions to the LIGO detector and the observation of gravitational waves". Observations are made in "runs". As of February 2026, LIGO has made four runs (with the third run divided into two "subruns" and the fourth divided into three subruns), and made 391 detections of gravitational waves. Maintenance and upgrades of the detectors are made between runs. The first run, O1, which ran from September 12, 2015, to January 19, 2016, made the first three detections, all black hole mergers. The second run, O2, which ran from November 30, 2016, to August 25, 2017, made eight detections: seven black hole mergers and the first neutron star merger. The third run, O3, began on April 1, 2019; it was divided into O3a, from April 1 to September 30, 2019, and O3b, from November 1, 2019 until it was suspended on March 27, 2020, due to COVID-19. The O3 run included the first detection of the merger of a neutron star with a black hole. The fourth run, O4, began on May 24, 2023, and ended on November 18, 2025. A total of 250 detection "candidates" were observed during O4, with 77 confirmed observations and the remaining 173 pending final analysis as of February 2026. Subsequent gravitational wave observatories Virgo in Italy and KAGRA in Japan, which both use interferometer arms 3 kilometres (9,800 ft) long, coordinated with LIGO to continue observations after the COVID-caused stop, with LIGO's O4 observing run operating from May 24, 2023 to November 18, 2025. During this time, LIGO had a sensitivity of 160–190 Mpc for binary neutron star mergers (sensitivities: Virgo 80–115 Mpc, KAGRA greater than 1 Mpc).

History

Background

… excerpt ends here. Continue reading the full article.

Illustrations

LIGO illustration
LIGO: LIGO Hanford Observatory
LIGO Hanford Observatory
LIGO: LIGO Louisiana Observatory
LIGO Louisiana Observatory
LIGO: Detector noise curves for Initial and Advanced LIGO as a function of frequency. They lie above the bands for space-borne detectors like the evolved Laser Interferometer Space Antenna (eLISA) and pulsar timing arrays such as the European Pulsar Timing Array (EPTA). The characteristic strains of potential astrophysical sources are also shown. To be detectable the characteristic strain of a signal must be above the noise curve.[59] These frequencies that aLIGO can detect are in the range of human hearing.
Detector noise curves for Initial and Advanced LIGO as a function of frequency. They lie above the bands for space-borne detectors like the evolved Laser Interferometer Space Antenna (eLISA) and pulsar timing arrays such as the European Pulsar Timing Array (EPTA). The characteristic strains of potential astrophysical sources are also shown. To be detectable the characteristic strain of a signal must be above the noise curve.[59] These frequencies that aLIGO can detect are in the range of human hearing.
LIGO: Simplified operation of a gravitational wave observatory Figure 1: A beamsplitter (green line) splits coherent light (from the white box) into two beams which reflect off the mirrors (cyan oblongs); only one outgoing and reflected beam in each arm is shown, and separated for clarity. The reflected beams recombine and an interference pattern is detected (purple circle). Figure 2: A gravitational wave passing over the left arm (yellow) changes its length and thus the interference pattern.
Simplified operation of a gravitational wave observatory Figure 1: A beamsplitter (green line) splits coherent light (from the white box) into two beams which reflect off the mirrors (cyan oblongs); only one outgoing and reflected beam in each arm is shown, and separated for clarity. The reflected beams recombine and an interference pattern is detected (purple circle). Figure 2: A gravitational wave passing over the left arm (yellow) changes its length and thus the interference pattern.

Worked examples

Example 1 — a first encounter with LIGO

Start with the simplest possible case. Write down what LIGO claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In astronomy, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to LIGO before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about LIGO ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of LIGO

In research
LIGO appears in astronomy research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry
Engineering practice reuses LIGO in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom
LIGO is common in secondary-school and first-year university syllabi. It links to neighbouring topics Astronomical observatories in Louisiana, Astronomical observatories in Washington (state), Buildings and structures in Benton County, Washington, so understanding it makes those chapters shorter.
In everyday life
Look for LIGO outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study LIGO in 20 minutes

  1. Read the reference excerpt below once, without taking notes.
  2. Close the page and write down what LIGO means in your own words.
  3. Compare your version with the excerpt and mark what you missed.
  4. Work through the three examples above with pen and paper.
  5. Explain LIGO out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is LIGO in simple terms?

The Laser Interferometer Gravitational-Wave Observatory (LIGO) is a large-scale physics experiment and observatory designed to detect cosmic gravitational waves. Prior to LIGO, all data about the universe had come in the form of light and other forms of electromagnetic radiation, from limited direc…

Why does LIGO matter?

Because it connects several astronomy ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study LIGO?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on LIGO.

Tags

  • Astronomical observatories in Louisiana
  • Astronomical observatories in Washington (state)
  • Buildings and structures in Benton County, Washington
  • Gravitational wave observatories
  • Hanford Site
  • Interferometric gravitational-wave instruments
  • Science and Technology Facilities Council

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