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Plans shape up for a revolutionary new observatory to explore black holes and the Big Bang

23 May 2011

Scientists present their design for Einstein Telescope – Europe’s next-generation detector that will ‘see’ the Universe in gravitational waves

A new era in astronomy will come a step closer when scientists from across Europe present their design study today for an advanced observatory capable of making precision measurements of gravitational waves – minute ripples in the fabric of spacetime – predicted to emanate from cosmic catastrophes such as merging black holes and collapsing stars and supernovae. It also offers the potential to probe the earliest moments of the Universe just after the Big Bang, which are currently inaccessible.

The Einstein Telescope (ET) is a so-called third-generation gravitational-wave (GW) detector, which will be 100 times more sensitive than current instruments. Like the first two generations of GW detectors, it is based on the measurement of tiny changes (far less than the size of an atomic nucleus) in the lengths of two connected arms several kilometres long, caused by a passing gravity wave. Laser beams passing down the arms record their periodic stretching and shrinking as interference patterns in a central photo-detector.

The first generation of these interferometric detectors built a few years ago (GEO600, LIGO, Virgo and TAMA) successfully demonstrated the proof-of-principle and constrained the gravitational wave emission from several sources. The next generation (Advanced LIGO and Advanced Virgo), which are being constructed now, should make the first direct detection of gravitational waves – for example, from a pair of orbiting black holes or neutron stars spiralling into each other. Such a discovery would herald the new field of GW astronomy. However, these detectors will not be sensitive enough for precise astronomical studies of the GW sources.

"The community of scientists interested in exploring GW phenomena therefore decided to investigate building a new generation of even more sensitive observatories. After a three-year study, involving more than 200 scientists in Europe and across the world, we are pleased to present the design study for the Einstein Telescope, which paves the way for unveiling a hidden side of the Universe," says Harald Lück, deputy scientific coordinator of the ET Design Study.

Professsor B.S. Sathyaprakash from Cardiff University’s School of Physics and Astronomy said: "Einstein Telescope will be an astronomical observatory to unveil the secret and hidden lives of neutron stars and black holes - the most compact objects in the Universe. ET will observe gravitational radiation arising from their collisions in binary systems when the Universe was still in its infancy, assembling the first galaxies and the large scale structure. ET will detect their formation when mature stars collapse and explode in violent supernovae and hypernovae. It will be sensitive to quakes in neutron stars and ripples on black holes caused by a colliding star or a black hole, providing us new insights into complex physical processes. ET will truly revolutionize our understanding of the Universe by impacting fundamental physics, cosmology and astrophysics."

The design study, which will be presented at the European Gravitational Observatory site in Pisa, Italy, outlines ET’s scientific targets, the detector layout and technology, as well as the timescale and estimated costs. I A superb sensitivity will be achieved by building ET underground, at a depth of about 100 to 200 metres, to reduce the effect of the residual seismic motion. This will enable higher sensitivities to be achieved at low frequencies, between 1 and 100 hertz (Hz). With ET, the entire range of GW frequencies that can be measured on Earth – between about 1 Hz and 10 kHz – should be detected. "An observatory achieving that level of sensitivity will turn GW detection into a routine astronomical tool. ET will lead a scientific revolution", says Michele Punturo, the scientific coordinator of the design study. An important aim is to provide GW information that complements observational data from telescopes detecting electromagnetic radiation (from radio waves through to gamma-rays) and other instruments detecting high-energy particles from space (astroparticle physics).

The strategy behind the ET project is to build an observatory that overcomes the limitations of current detector sites by hosting more than one GW detector. It will consist of three nested detectors, each composed of two interferometers with arms 10 kilometres long. One interferometer will detect low-frequency gravitational wave signals (2 to 40 Hz), while the other will detect the high-frequency components. The configuration is designed to allow the observatory to evolve by accommodating successive upgrades or replacement components that can take advantage of future developments in interferometry and also respond to a variety of science objectives.

The European Commission supported the design study within the Seventh Framework Program (FP7-Capacities) by allocating three million Euro.

"With this grant, the European Commission recognized the importance of gravitational wave science as developed in Europe, its value for fundamental and technological research, provided a common framework for the European scientists involved in the gravitational wave search and allowed for a significant step towards the exploration of the Universe with a completely new enquiry instrument", says Federico Ferrini, director of the European Gravitational Observatory (EGO) and project coordinator of the design study for the Einstein Telescope.

ET is one of the 'Magnificent Seven' European projects recommended by the ASPERA network for the future development of astroparticle physics in Europe. It would be a crucial European research infrastructure and a fundamental cornerstone in the realisation of the European Research Area.

-Ends-

Notes:

Further information, images and movies: www.et-gw.eu

Professor B Sathyaprakash

Cardiff University

School of Physics and Astronomy

E-mail: B.Sathyaprakash@astro.cf.ac.uk

Tel.: 029 208 76962

Mobile: 0773 6121076

www.astro.cardiff.ac.uk/pub/B.Sathyaprakash

Dr Thomas Dent

Cardiff University

School of Physics and Astronomy

E-mail: Thomas.Dent@astro.cf.ac.uk

Tel: 029 208 76964

Dr Peter Sutton

Cardiff University

School of Physics and Astronomy

E-mail: Patrick.Sutton@astro.cf.ac.uk

Tel: 029 208 74649

Susanne Milde

E-mail: milde@mildemarketing.de

Tel: +49 331 583 93 55

• The Einstein Telescope Project (ET) is a joint project of eight European research institutes, under the direction of the European Gravitational Observatory (EGO). The participants are EGO, an Italian French consortium located near Pisa (Italy), Istituto Nazionale di Fisica Nucleare (INFN) in Italy, the French Centre National de la Recherche Scientifique (CNRS), the German Max Planck Institute for Gravitational Physics (Albert Einstein Institute) in Hannover, the Universities of Birmingham, Cardiff and Glasgow in the UK, and the Dutch Nikhef in Amsterdam. Scientists belonging to other institutions in Europe, as well as the US and Japan, actively collaborated in the realisation of this design study.

• The direct detection of gravitational waves – predicted by Einstein’s theory of gravity, the General Theory of Relativity – is one of the most important fundamental research areas in modern science. Apart from verifying General Relativity, especially for extreme gravitational fields found in the vicinity of a black hole, GW detection could allow us, for the first time, to look back at the earliest moments of the Universe just after its birth. Cosmological observations are currently limited to those using electromagnetic waves and cosmic-rays (high-energy particles such as protons). This information can reach us from the past, but from a time no earlier than 380,000 years after the Big Bang. Before then, light and matter continually interacted, so that the Universe was rendered opaque. The Universe became transparent only when matter and light separated during this epoch. Cosmological epochs dating further back have thus far remained hidden, so it has not been possible to verify from observations the various theories about their nature. The direct measurement of gravitational waves may allow us "to listen" back as far as the first trillionth of a second after the Big Bang. This would give us totally new information about our Universe.

• GW research is a global effort because the full information about many GW sources can be obtained only with several interferometers working simultaneously in different places. Therefore, the US (LIGO), German-UK (GEO600), Italian-French and Dutch (Virgo) scientific communities have been working together closely for a long time. They share technology R&D and theoretical advances, as well as data-analysis methods and tools. The joint European project ET will help to improve further this worldwide collaboration.

The current observatories:

• GEO600, is a German-UK detector located near Hannover, Germany, and is operated by researchers at the Max Planck Institute for Gravitational Physics (Albert Einstein Institute/AEI) in Hannover, and at the Universities of Glasgow, Cardiff and Birmingham in the UK. It is funded by the Max Planck Society, the state of Lower Saxony, the Volkswagen Foundation and the UK Science and Technologies Facilities Council (STFC). GEO works in close cooperation with the cluster of excellence, QUEST (Centre for Quantum Engineering and Space-Time Research) at the Leibniz Universität Hannover.

URL: www.geo600.de

• Virgo is a 3-kilometre arm interferometer at Cascina, near Pisa, Italy. This project accomplished the additional goal of making low-frequency measurements at around 10Hz. Initially, Virgo was funded by the CNRS (Centre National de la Recherche Scientifique) and the INFN (Istituto Nazionale di Fisica Nucleare) but has now expanded to include Dutch, Polish and Hungarian research groups.

URL: www.virgo.infn.it

• The US LIGO detectors consist of 2-kilometre and 4-kilometre instruments at Hanford, Washington, and a 4-kilometre instrument at Livingston, Louisiana. The LIGO project has been developed and is operated by the California Institute of Technology (CalTech) and the Massachusetts Institute of Technology (MIT), and funded by the National Science Foundation (NSF). A

URL: www.ligo.caltech.edu

The Gravitational Physics Group at Cardiff University. The School of Physics and Astronomy, has a very active astrophysics programme with 32 academic staff and over 100 researchers in all and has its own computational facilities and a world-class instrumentation lab. The research groups are involved in a number of key observational projects including Planck, Herschel, GEO600, LISA, LIGO, and the Square Kilometer Array.

The Gravitational Physics Group at Cardiff comprises 5 faculty, 5 post-doctoral fellows and 10 PhD students. Direct detection of gravitational waves has been the focus of research of the Gravitational Physics group for over two decades. The quest for gravitational waves has been the driving force ever since the group, jointly with the Universities of Glasgow and Hanover and the Albert Einstein Institute (Golm and Hanover), led the proposal to build the British-German GEO 600 interferometer. The group is an integral member of the LIGO Scientific Collaboration (LSC) and is involved in all other major gravitational-wave interferometer projects, LIGO, Virgo and LISA.

It collaborates widely, with some twenty institutions (e.g. AEI, Caltech, IAP, IHES, MIT, Moscow, Tokyo, and UWM) in four continents (US, Europe, Asia and Australia). Members of the group hold leadership positions in international projects: Fairhurst is the Co-Chair for the

Compact Binary Coalescence working group of the LSC, Sathyaprakash is the Chair of the WG4 of the Einstein Telescope Design Study, Sutton is the co-ordinator of the Externally Triggered Searches subgroup of the LSC Burst working group and Schutz is a member of the LSC Executive Committee and LISA International Science Team.

In the early years of the GEO 600 project, i.e. during 1998-2004, the group worked on algorithm and software development for quick-look analyses, the design and implementation of GEO 600's data acquisition system, the characterization of data from GEO 600, the development of the necessary search algorithms, and building computational resources and data archives at Cardiff. Since 2004 the group has embarked upon the ultimate goal in this field: the detection of gravitational waves in the data from the GEO 600, LIGO and Virgo detectors, with the group's effort predominantly spent in searching for what is believed to be the most promising class of astronomical sources, namely the coalescence of binary neutron stars and black holes. The group also researches into the theoretical aspects of gravitational waves sources, specializing in the production of a stochastic background of gravitational waves in the primordial Universe and modelling the late time dynamics of binary black holes. Many of the data analysis algorithms founded by the members of the group are today routinely used in the search for gravitational waves.