Plans shape up for a revolutionary new observatory to explore black holes and the Big Bang
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 Observatory (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. 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.
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 dimension
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.
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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: