At the threshold of gravitational-wave astronomy

The Science Museum in London presents an exhibition devoted to current gravitational wave research. Opening of the exhibition Cosmos & Culture on 23 July.

July 21, 2009

The AEI will provide a full-scale model of a LISA satellite

As part of the exhibition Cosmos & Culture, the Science Museum in London will display for the first time an exhibition devoted to current gravitational wave research and the related technological development. As a special highlight, a full-scale model of a LISA satellite, a loan from the Max Planck Institute for Gravitational Physics (Albert Einstein Institute/AEI), will be on display.  LISA stands for Laser Interferometer Space Antenna, certainly one of the most exciting projects set to measure gravitational waves and one of the biggest joint space missions between NASA and ESA. The space observatory will be created via a triangular formation of three satellites that will be linked to one another through a five million-kilometre long laser beam and will orbit the Sun while flying in an Earth-like orbit. LISA is expected to be launched in 2020. Already in 2011, LISA’s highly precise technology will be tested in space: with the LISA pathfinder mission, which will be spearheaded by ESA.

“For us scientists from the AEI it is a special honour to provide a glimpse into the future at the London Science Museum. The AEI has gladly provided the renowned museum with a 1:1 model of a LISA satellite,” says Prof. Dr. Karsten Danzmann, Director at the AEI and scientific head of the LISA mission on the European side.

Central elements of the earthbound gravitational wave observatories will also be on display, including: a 25 cm and 23 kg heavy prototype test mass of the purest synthetic sapphire that was manufactured for the research and development work within the framework of the German-British GEO collaboration. The test mass is a key element for precision measurements with a laser interferometer. A laser beam will be reflected onto it, be intensified and send back again to the point of departure. It “tracks down” the gravitational wave that passes through. The extremely high-grade test masses are being developed at the Gravitational Research (IGR) at the University of Glasgow in Scotland. And that’s also where the displayed prototype comes from.

In addition, a prototype of a test mass suspension will be shown the way it will soon be installed in the next generation of American gravitational wave detectors (Advanced LIGO). The 2 m high multiple pendulum suspension will play an important role in increasing LIGO’s measuring precision because it decouples the test mass considerably better from seismic disturbances than the predecessor model. This allows for more precise measurements by the laser interferometer. The scientists working on the project consider disturbances in this connection as even the most miniscule tremors, for example a car driving by miles and miles away or an earthquake in Japan. The multiple pendulum suspension was developed at the GEO600 detector under the direction of the Rutherford Appleton Laboratory.

The measurement of gravitational waves - and thus gravitational physics - is one of the key features of the fascinating special exhibition Cosmos & Culture in the Science Museum London. The exhibition will open on 23 July and run until the end of 2010.

Background information

Cosmos & Culture – The exhibition
Humans have been observing the stars since the Stone Age. For humans, the heavens were both clock and compass, and always a source of wonder. Our understanding of the universe has changed again and again since the earliest times, just as astronomy itself, as a science that amazes and fascinates. With its unique collection, the special exhibition in the London Science Museum tells the story of the relationship between humans and stars. Cosmos & Culture creates a bridge between the historic legacy of ancient astronomy to the innovative and pioneering technologies of the 21st century.  The measurement of gravitational waves is, in this connection, a special challenge - and a source of completely new knowledge about time and space.

Gravitational wave astronomy
Already today we can observe the universe in numerous wavelengths: with the help of telescopes that survey the cosmos in the optical, infrared, gamma and x-ray areas. With gravitational wave astronomy, we will be able, for the first time, to listen in on the universe - and thereby obtain totally new insights. We will be able to hear colliding black holes and the echo of the Big Bang - and we will learn much about the development of our universe. There is still a great deal to discover - after all, around 96% of the universe is unknown. Direct proof of gravitational waves is clearly one of the most exciting tasks facing modern physics. In 1916 Albert Einstein predicted the existence of gravitational waves in his general theory of relativity. They occur when, for example, two black holes collide with one another. We will soon be able to actually hear these tiny ripples in space-time. Just how tiny gravitational waves are is clear from this example: Gravitational waves from a supernova explosion in a neighbouring galaxy alter the length of a 1 km long test track on Earth by only one one-thousandth of the diameter of a proton and that for only a few thousandths of a second.

Gravitational wave observatories on Earth - technology and outlook
Numerous gravitational wave detectors of the first generation are currently up and running: The German-British GEO600 gravitational wave detector is located near Hannover and is operated by researchers from the AEI, as well as from the British Universities of Glasgow, Cardiff and Birmingham. The GEO project is financed by the Max Planck Society, as well as the British Science and Technologies Facilities Council (STFC). In the area of technology development, GEO600 plays a pioneering role globally, and is seen as an international think-tank of gravitational wave research. In the areas of research, technology development and data evaluation, GEO scientists work closely with their American colleagues from the LIGO project. The French-Italian-Dutch Virgo Project, the Japanese TAMA and Australian AIGO Projects are also part of the international cooperation.

Each of the L-shaped interferometers uses a laser whose light is split into two beams. These laser beams constantly run back and forth through a vacuum tube between two mirrors. Via the laser beams, the distance between the exactly positioned mirrors is measured. Should a gravitational wave pass through the detector, then, according to Albert Einstein's general theory of relativity, the distance between the mirrors must change minimally, when a gravitational wave - a distortion of space-time that is propelled through the universe by a greatly accelerated massive object - passes the detector. The interferometer is so sensitive that it can recognize a change in length of a laser arm of less than a thousandth of the diameter of an atom.

During the next decade, all of the currently operating interferometric gravitational wave detectors - GEO600, LIGO und Virgo - will be upgraded with instruments of the second generation.

LISA, the gravitational wave observatory in space
Starting around 2020, LISA will augment the earthbound gravitational wave detectors and listen even more deeply into the universe. LISA’s extreme sensitivity will enable the most precise measurements and thus a glimpse back into the history of our universe, in a way that no other technology can manage. In addition to many other results, LISA will observe with great precision how black holds merge with one another and how larger black holes are born. Moreover, with LISA, scientists will be able to tell their colleagues at the optical telescopes, before an event like the merging of two super-heavy black holes, in which direction they must look. LISA will also be able to observe events that took place very far in the past - down to the very first type of these.

And LISA will also be able to determine the “history of the tempo of expansion of our universe” and make a substantial contribution to clearing up the physical characteristics of the mysterious “dark energy” - which today is pushing the expansion of the universe with ever-increasing speed. LISA’s prospects of measuring the expansion of the universe is based on a discovery by AEI Director Bernard Schultz in 1986: He proved that, from the gravitational signals from black holes that are encircling one another, we can derive their exact distance from us. This is the most dependable distance measurement that astronomers have at their disposal today for such immense distances.

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