The European Pulsar Timing Array (EPTA) is a European collaboration to combine five 100-m class radio-telescopes to observe an array of pulsars with the specific goal of detecting gravitational waves. It competes with the Australian and American pulsar timing arrays, the Parkes Pulsar Timing Array and the North American Nanohertz Observatory for Gravitational Waves

North American Nanohertz Observatory for Gravitational Waves

The North American Nanohertz Observatory for Gravitational Waves is a consortium of astronomers who share a common goal of detecting gravitational waves via regular observations of an ensemble of millisecond pulsars using with the Green Bank and Arecibo radio telescopes...

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Pulsars and high-precision timing

Pulsars are rapidly rotating, highly magnetized neutron stars that emit radio waves from their magnetic poles that are observed as pulses. Due to the extremely high density of neutron stars, their rotation periods are very stable, hence the observed arrival time of the pulses are highly regular. These arrival times are called TOA's (time of arrival) and can be used to perform high-precision timing experiments.

The stability of the TOA's from most pulsars is limited due to the presence of red noise, also called "timing noise". However, there is a special class of pulsars, called millisecond pulsars (MSP), that are shown to suffer from little or no timing noise. By keeping track of the TOA's of different MSP's over the sky allows for a high-precision timing experiment to detect one of the holy grails of physics: gravitational waves.

Detection of gravitational waves

Gravitational waves (GW) are small disturbances in space-time, caused by the motion of masses. These waves are so weak that only the strongest waves, caused by rapid motion of dense stars or black-holes, have a chance of being detected. A pulsar timing array (PTA) uses an array of MSP's as the endpoints of a galaxy-scale GW detector

Gravitational wave detector

A gravitational wave detector is any experiment designed to measure gravitational waves, minute distortions of spacetime that are predicted by Einstein's theory of general relativity. The existence of gravitational radiation is a prediction of Einstein's general theory of relativity. Gravitational...

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sensitive to GW's with a frequency in the nano-Hertz regime, which corresponds to the regime of the stochastic GW background caused by the coalescence of super-massive black holes in the early universe. This makes PTA's complementary to other GW detectors such as LIGO

LIGO

LIGO, which stands for the Laser Interferometer Gravitational-Wave Observatory, is a large-scale physics experiment aiming to directly detect gravitational waves. Cofounded in 1992 by Kip Thorne and Ronald Drever of Caltech and Rainer Weiss of MIT, LIGO is a joint project between scientists at MIT,...

, VIRGO

Virgo

-Astronomy:* Virgo Cluster, a cluster of galaxies in the constellation Virgo* Virgo , a constellation* Virgo Stellar Stream, remains of a dwarf galaxy* Virgo Supercluster, a galactic supercluster-Surname:* Virgo...

 and LISA

Lisa

-People:* Lisa * Lisa , Japanese singer and producer* LiSA, Japanese singer* Esteban Lisa, Argentine painter-Information technology:* Apple Lisa computer, the precursor to the Apple Macintosh* Lisa assembler, a 6502 assembler for Apple II...

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Telescopes

The EPTA uses five European telescopes. These are the Westerbork Synthesis Radio Telescope

Westerbork Synthesis Radio Telescope

The Westerbork Synthesis Radio Telescope is an aperture synthesis interferometer near camp Westerbork, north of the village of Westerbork, Midden-Drenthe, in the northeastern Netherlands. It consists of a linear array of 14 antennas with a diameter of 25 metres arranged on a 2.7 km East-West line...

, the Effelsberg Radio Telescope, the Lovell Telescope

Lovell Telescope

The Lovell Telescope is a radio telescope at Jodrell Bank Observatory, near Goostrey, Cheshire in the north-west of England. When it was constructed in 1955, the telescope was the largest steerable dish radio telescope in the world at 76.2 m in diameter;it is now the third largest, after the...

, the Nançay Radio Telescope

Nançay Radio Telescope

The Nançay Decimetric Radio Telescope is located in the small commune of Nançay, two hours' drive south of Paris, France. The radio telescope saw first light in 1965, after an inauguration by the then French president, Charles de Gaulle. It is one of the largest radio telescopes in the world...

 and the Sardinia Radio Telescope

Sardinia Radio Telescope

The Sardinia Radio Telescope is a large, fully steerable radio telescope currently being completed near San Basilio, province of Cagliari in Sardinia, Italy. It is a collaboration among the Istituto di Radioastronomia di Bologna, the Cagliari Astronomy Observatory and the Arcetri Astrophysical...

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LEAP

Recently the EPTA has made a giant "leap" forward thanks to European funding of the Large European Array for Pulsars (LEAP). This project involves coherently combining the five EPTA-telescopes to make the equivalent of a fully steerable 194-m dish. This will improve the accuracy with which the TOA's can be measured by an order of magnitude, possibly leading to a first detection of GW's around 2015.