Listening posts around the globe

Overview of the gravitational wave detectors currently operational, or under construction

An article by Badri Krishnan, Carsten Aulbert

Currently, scientists in listening posts all across the globe are busily detecting gravitational waves, upgrading the existing detectors and planning new ones.

Before we start describing the different projects, here is a map of their locations:

locations of current gravitational wave detectors on a world map, two detectors are located in North America, two in Europe, one in India and one in Japan

Interferometric detectors

The state of the art in search of gravitational waves are the interferometric detectors which have been under development since the 1980s and whose technology continues to be improved and refined. After long periods of planning and constructions, there are currently the following projects:

GEO600 has an arm-length of 600m and is located in Ruthe, Germany (near Hanover). It is operated by the Max Planck Institute for Gravitational Physics in Hanover. The GEO collaboration consists of 250 members and is part of the LIGO scientific collaboration.

LIGO is an abbreviation for “Laser Interferometer Gravitational Wave Observatory”. The LIGO project has two interferometric detectors in the United States, “Advanced LIGO”, each with arm lengths of 4 kilometres. They are located in Hanford, Washington, and Livingston, Louisiana. A third detector of the LIGO network has been under construction in India in 2020.

Virgo is a European detector with an arm-length of 3 kilometres near Pisa in Italy. The initial detector, Virgo, was upgraded to achieve 10 times higher sensitivity and started operation as Advanced Virgo in 2017.

KAGRA (Kamioka Gravitational Wave Detector) is an underground gravitational wave detector in the Kamioka mine in Japan. It uses cyrogenic technology, which means that the mirrors are cooled down to 20 Kelvin in order to reduce thermal noise. The detector has been in operation since 2020.

Planned projects

LISA (Laser Interferometer Space Antenna) is an ESA/NASA project for a space-based interferometric gravitational wave detector. LISA consists of three spacecraft in orbit around the Sun moving in the formation of a near-equilateral triangle whose sides are 2.5 million kilometres long. LISA is currently scheduled to launch in 2034.

Cosmic Explorer is a proposed third generation interferometric gravitational wave detector. It will be built in the United States and is designed with an L-shaped geometry, each arm being up to 40 kilometers in length to achieve greater sensitivity than ever before.

The Einstein Telescope is planned as an underground third generation gravitational wave detector in Europe with arm lengths of 10 kilometers. Underground installation, as for KAGRA, is supposed to reduce the influence of Newtonian and seismic noise.

NEMO (Neutron Star Extreme Matter Observatory) is an Australian project that has so far proposed a design for a gravitational wave interferometer optimized to specifically study neutron star mergers.

Resonant detectors

The first type of gravitational wave detectors were resonant mass antennas. The center piece of such a detector is a solid metal object. Passing gravitational waves make that central test-mass oscillate, and these oscillations can be measured and amplified to detect the gravitational waves. Such antennas were set up in Rome (NAUTILUS) and Padova (AURIGA), Italy, in Geneva (EXPLORER) , Switzerland, in the US (ALLEGRO), and in Perth (NIOBE), Australia, forming the International Gravitational Event Collaboration. Yet, the sensitivity of these early instruments did not seem to allow efficient detection of gravitational waves. However, third generation resonant mass antennas, which use spherical test masses, are still in operation at Leiden (MiniGRAIL), The Netherlands, and Sao Paulo, Brazil (Mario Schenberg).

Further Information

For background information on gravitational waves, check out Elementary Einstein, particularly the chapter Gravitational waves. Related Spotlight topics on Einstein-Online can be found in the section Gravitational waves. This article from 2010 was updated in November 2020 with contributions from Harald Lück, Albert Einstein Institute/ Leibniz University Hanover.

Watch a short video about GEO600 on YouTube (German, with English subtitles).

Colophon

Badri Krishnan

is a physicist and professor at the Institute for Mathematics, Astrophysics and Particle Physics at Radboud University, The Netherlands.

Carsten Aulbert

is a scientist at the Albert Einstein Institute in Hanover.

Citation

Cite this article as:
Badri Krishnan, Carsten Aulbert, “Listening posts around the globe” in: Einstein Online Band 12 (2020), 12-1003

Definitioner

KAGRA

Der Kamioka Gravitational Wave Detector (KAGRA) ist ein unterirdischer japanischer Gravitationswellendetektor mit drei Kilometer langen Armen. KAGRA zeichnet sich durch die verwendete Kyrotechnik aus, das heißt, die Spiegel des Interferometers werden auf 20 Kelvin gekühlt, um thermisches Rauschen zu reduzieren. Die unterirdische Bauweise verspricht darüber hinaus ein reduziertes seismisches Rauschen. Der Detektor ging 2020 in den Beobachtungsbetrieb.

KAGRA

The Kamioka Gravitational Wave Detector (KAGRA) is an underground Japanese gravitational wave detector, the length of its two arms being 3 km. KAGRA uses cyrogenic technology, which means that the interferometer’s mirrors are cooled down to 20 Kelvin in order to reduce thermal noise. On top of that, the underground construction is expected to reduce seismic noise. The detector has started observation in 2020.

Virgo

Virgo is a gravitational wave detector that was collaboratively built by French and Italian labs and was in operation until 2011. Then, the instrument was decommissioned and adapted to achieve 10 times higher sensitivity. Advanced Virgo started operation in 2017. Together with LIGO, GEO600 and KAGRA, it has since served the purpose of investigating space using gravitational wave signals.

Virgo

Virgo ist ein französisch-italienischer Gravitationswellendetektor, der zunächst bis 2011 in Betrieb war und anschließend zu Advanced Virgo umgebaut wurde, der zehnmal empfindlicher sein soll. Dieser ging 2017 in den Betrieb. Seither dient er zusammen mit LIGO, GEO600 und KAGRA der Erforschung des Weltalls mithilfe von Gravitationswellensignalen.

Laser Interferometer Gravitational Wave Observatory

Siehe LIGO

LISA

Über 20 Jahre wurde LISA (Laser Interferometer Space Antenna) als Konzept eines weltraumbasierten Gravitationswellendetektors gemeinsam von den europäischen und amerikanischen Weltraumbehörden ESA und NASA voran getrieben. Es soll ein interferometrischer Detektor aus drei Satelliten, angeordnet in einem Dreieck mit 2,5 Million Kilometer Kantenlänge entstehen, welcher vom Weltraum aus nach Gravitationswellen suchen soll. Zwischenzeitlich eLISA benannt, heißt das Projekt wieder LISA und soll 2034 starten. LISA-Website

Laser Interferometer Space Antenna (LISA)

LIGO

Laser-Interferometer-Gravitationswellenobservatorium: ein Detektor für Gravitationswellen in den USA, welcher zwischen 2010 und 2015 zum Advanced LIGO ausgebaut wurde. Der Detektor besteht aus zwei interferometrischen Gravitationswellendetektoren, mit jeweils vier Kilometern Armlänge. Einer davon steht in Hanford im US-Bundesstaat Washington, ein weiterer in Livingston im US-Bundesstaat Louisiana. An LIGO wurden 2015 die ersten Gravitationswellen direkt nachgewiesen. LIGO-Webseiten

Advanced LIGO (LIGO)

Laser

Abkürzung für "Light Amplification by Stimulated Emission of Radiation", zu deutsch etwa: Lichtverstärkung durch stimulierte Strahlungsaussendung. Verfahren zur Erzeugung sehr konzentrierten, starken Lichtes mit fester Frequenz, das in Form einer sehr gleichförmigen elektromagnetischen Welle ausgesendet wird. Dabei haben alle ausgesendeten Wellen jeweils zur gleichen Zeit ihre Maxima und Minima ("kohärentes Licht").

Laser Interferometer Space Antenna

Siehe LISA

Kelvin (Kelvin-Temperaturskala)

In der Physik übliche Temperaturskala, synonym: absolute Temperaturskala. Außerdem die Maßeinheit für Temperatur gemäß dem Internationalen Einheitensystem. Nullpunkt ist der absolute Nullpunkt; ein Temperaturunterschied von einem Kelvin (abgekürzt 1 K, manchmal auch "ein Grad Kelvin") ist dasselbe wie ein Unterschied von einem Grad Celsius, denn die beiden Skalen unterscheiden sich nur durch die Wahl des Nullpunkts: X Grad Celsius sind X plus 273,15 Kelvin, Y Kelvin sind Y minus 273,15 Grad Celsius. Beziehung zu der in den USA üblichen Fahrenheit-Skala: X Grad Fahrenheit sind (X+459,67)*5/9 Kelvin, Y Kelvin sind (Y*9/5)-459,67 Grad Fahrenheit.

ESA (European Space Agency)

Europäische Weltraumagentur; beteiligt an Projekten wie dem Weltraumteleskop Hubble oder dem Gravitationswellendetektor LISA.

ESA-Webseiten

Neutron

Elektrisch neutrales, vergleichsweise massives Teilchen; die Kerne der Atome bestehen aus Neutronen und Protonen.

Neutronen sind keine Elementarteilchen, sondern bestehen ihrerseits aus Quarks, die von der starken Kernkraft zusammengehalten werden. Neutronen, Protonen und eine Reihe ähnlicher Teilchen werden zusammengefasst als Baryonen bezeichnet.

Verschiedene Arten von Neutronenmaterie sind der Stoff, aus dem Neutronensterne sind.

wave

In a general sense: any travelling pattern, whether or not it involves matter being transported as well. Simple examples are water-waves - wave crests and troughs travelling over a water surface, and a Mexican wave in a football stadium, with fans alternately standing up and sitting down - the pattern moves throught the stadium, not the fans themselves.

An especially simple form for a wave is a sinus wave, a regular pattern of wave crests and troughs.

waves (wave)

An especially simple form for a wave is a sinus wave, a regular pattern of wave crests and troughs.

triangle

In a plane and other flat space: Geometrical object consisting of three points ("vertices") with three connecting straight lines. The definition can be made more general, in a way that applies to curved spaces, as well: A geometric object consisting of three points ("vertices") connected by three segments of geodesics.

star

A cosmic gas ball that is massive enough for pressure and temperatur in its core to reach values where self-sustained nuclear fusion reactions set in. The energy set free in these reactions makes stars into very bright sources of light and other forms of electromagnetic radiation. Once the nuclear fuel is exhausted, the star becomes a white dwarf, a neutron star or a black hole.

space

In a strict sense: Space as we know it from everyday life: the totality of all locations in which objects can sit, with three dimensions. In a more general sense used by mathematicians, all kinds of sets of points are spaces - a line for instance, which has but a single dimension, or a two-dimensional surface, but also higher-dimensional spaces. Also, in such more general spaces, geometry can be different from the standard Euclidean geometry taught in high schools - such spaces can be curved.

neutron

Particle that is electrically neutral and comparatively massive; the atomic nuclei consist of neutrons and protons. Neutrons are not elementary particles, they are compound particles consisting of quarks that are bound together through the strong nuclear interaction . Collectively, neutrons, protons and a number of similar particles are called baryons. Neutron stars are mainly made of neutrons.

neutron star

Final stage of massive stars that explode as a supernova. In the explosion process, the core of the star collapses to form a compact object with roughly 1.4 solar masses that mostly consists of nuclear matter, predominantly of neutrons. For astronomers, neutron stars are of interest as there exists a variety called pulsars from which they receive highly regular pulses of electromagnetic radiation. For relativists, they are interesting as the typical effects of general relativity are very pronounced in objects that compact (compare PSR 1913+16, double pulsar PSR J0737-3029A/B).

NASA (National Aeronautics and Space Administration (NASA))

Part of the US government in charge not only of manned space missions, but also responsible for numerous highly successful satellite and probe missions. NASA is a partner in projects such as the Hubble space telescope or the gravitational wave detector LISA. NASA website

LISA

The concept of LISA (Laser Interferometer Space Antenna), a space-based gravitational wave detector, has been studied jointly by the European and US space agencies ESA and NASA for 20 years. The planned interferometric gravitational wave detector should be composed of three satellites, positioned to form a triangle, with each side 2.5 million kilometers long. While called eLISA for some time, the project named LISA is expected to launch in 2034. > LISA website

Laser Interferometer Space Antenna (LISA)

LIGO

Laser Interferometer Gravitational-Wave Observatory : A detector project for the measurement of gravitational waves in the United States, which was upgraded to the Advanced LIGO between 2010 and 2015 .The detector includes two interferometric gravitational wave detectors, with an arm-length of four kilometers each. One of them is located in Hanford, Washington, the other one is located in Livingston, Louisiana. The first ever direct measurement of gravitational waves was made at LIGO. > LIGO website

Laser Interferometer Space Antenna

See LISA

Laser Interferometer Gravitational Wave Observatory

See LIGO

interferometric gravitational wave detector (interferometric detector)

Gravitational wave detector that utilizes interference between light waves to detect minute changes in distance effected by a passing gravitational wave. Some of the physics behind interferometric detectors can be found in our spotlight topic Catching the wave with light. Exmples for interferometric detectors are GEO600 and the LIGO detectors.

gravitational waves

Distortions of space geometry that propagate through space with the speed of light, analogous to ripples on the surface of a pond propagating as water waves. For more informations about gravitational waves, please consult the chapter Gravitational waves of Elementary Einstein. Selected aspects of gravitational wave physics are described in the category Gravitational waves of our Spotlights on relativity.

gravitational wave detector

Currently, scientists world wide are attempting the direct measurement of gravitational waves reaching us from the depths of space. They are mainly using two types of detectors: interferometric detectors like GEO600 and the LIGO detectors, and resonant detectors. For more informations about gravitational waves, please consult the chapter Gravitational waves of Elementary Einstein.

geometry

That part of mathematics concerning itself with surfaces or more general spaces as well as objects defined on such spaces, such as points or lines as well as the objects constructable from points and lines, such as triangles.

ESA (European Space Agency)

The European Space Agency coordinates the space-faring activities of the European countries. It is a partner in projects such as the Hubble space telescope and the gravitational wave detector LISA. ESA website

Albert Einstein Institute

One of the research institutes of the Max Planck Society; an international centre for research on Einstein's theory of gravity - from the mathematical fundamental, astrophysics and gravitational waves to quantum gravity. Founded in 1995, the institute is situated in Golm near Potsdam in Germany. In 2002, the experimental branch of the institute was opened in Hannover. It is dedicated to research with the gravitational wave detector GEO 600 . AEI webpages Website of AEI-Hannover