Plans Shape Up for a Revolutionary New Observatory to Explore Black Holes and the Big Bang

University of Birmingham physicists, with scientists from all over the world, present their design for the 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 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, 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 gravitational 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 high precision studies of the GW sources.

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 from astronomical sources that can be measured on Earth – between about 1 Hz and 10 kHz – should be detected. 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 Birmingham Gravitational Wave Group is centred on the observation of the universe in the gravitational wave band, and on testing gravity at new scales. The group is a member of the GEO collaboration and the LIGO Scientific Collaboration with a central role in data analysis and the instrumental upgrade of LIGO to Advanced LIGO. It is also part of the LISA-Pathfinder team providing flight hardware for the proposed NASA / ESA mission to detect gravitational waves from space. The group has played a leading role in the design of the next generation of detectors - Advanced Virgo and the Einstein Telescope. Dr Andreas Freise, from the University of Birmingham’s School of Physics and Astronomy, who leads the optical design of the Einstein Telescope said, ‘The Einstein Telescope is an amazing instrument. It combines many new ideas and technologies custom built to create the most sensitive instrument to listen to the faint echoes in the fabric of space and time. I helped to build the GEO 600 and Virgo detectors and later had the chance to contribute to the optical design for Advanced Virgo. Now leading the optical design of the Einstein Telescope has been a great opportunity, using hands- on experience to design something completely new.’

Professor Alberto Vecchio, who leads the LIGO activities at the University of Birmingham, said, ‘We expect to achieve the first direct detection of gravitational waves with Advanced LIGO, to which our group has made direct contributions. As new ideas mature the Einstein Telescope becomes the next natural step in the quest for observing the universe with new "eyes", and a bold step beyond Advanced LIGO: with its exquisite sensitivity the Einstein Telescope will enable us to produce precise maps of black holes, unveiling many of their mysteries, and possibly peek into the first moments of cosmic history after the Big Bang.’

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.