In a meeting on 20 June 2017 ESA’s Science Programme Committee selected the space-based gravitational-wave detector “Laser Interferometer Space Antenna” (LISA) for ESA’s third large (L3) mission in the “Cosmic Vision” plan. LISA will consist of three spacecraft separated by millions of kilometers. They will precisely monitor their relative distance changes with lasers to detect gravitational waves in space. Researchers at the Max Planck Institute for Gravitational Physics Hannover and the Institut für Gravitationsphysik at Leibniz Universität Hannover are leading members of the international LISA consortium. LISA will complement ground-based gravitational-wave detectors by observing these space-time ripples at low frequencies, which are emitted by, e.g., merging supermassive black holes, and binary stars. After the selection on the 20th of June, the design and costing of the mission will now be completed. It will then be proposed for “adoption” by ESA, followed by the construction of the spacecraft. The launch of the mission is expected in 2034.
“After 25 years of hard work, developing and planning our gravitational-wave detector in space, I am very pleased to witness this day which marks the birth of the LISA mission. LISA will be a unique observatory and will revolutionize our understanding of the universe,” says Karsten Danzmann, director at the Max Planck Institute for Gravitational Physics Hannover and director of the Institut für Gravitationsphysik at Leibniz Universität Hannover. “With LISA we might be able to listen to the echo of the Big Bang, and will hear the sounds of supermassive black hole pairs merging anywhere in the entire universe.”
Gravitational-Wave Observation from Space
The proposed LISA mission will detect gravitational waves in space using a trio of satellites, separated by millions of kilometers. Lasers will be employed to measure the minute changes in their relative distance induced by impinging gravitational waves.
Einstein predicted the existence of gravitational waves from his general theory of relativity. They were — 100 years after their prediction — observed for the first time by the ground-based Advanced LIGO detectors in September 2015. Two other clear detections followed. Space-borne observatories such as LISA will complement the existing ground-based detectors by measuring low-frequency gravitational waves inaccessible from Earth.
The signals seen by ground-based detectors have frequencies between tens of hertz and several kilohertz, but gravitational waves span a much wider spectrum. In particular, lower frequency waves are produced by events such as the mergers of supermassive black holes millions or billions times the mass of our Sun, millions of binary stars in our galaxy, or exotic events such as cosmic strings.
LISA Pathfinder Paved the Way
Detecting the gravitational waves emitted from these events at frequencies between 0.1 millihertz and 1 hertz requires measuring the distance changes between objects placed millions of kilometers apart to a picometer. This can only be achieved in space, where an observatory would also be free of the seismic, thermal, and terrestrial gravity noises that limit ground-based detectors.
LISA Pathfinder is an ESA satellite mission, designed to demonstrate key technologies needed to build LISA. It has proven those technologies beyond any doubt and has exceeded all expectations. At the end of June, after sixteen months of science operations, LISA Pathfinder will complete its mission.
Building and Launching LISA
In 2013 ESA chose the “Gravitational Universe” science theme for its L3 mission. The 20th of June selection of the LISA mission is the second step towards a gravitational-wave observatory in space. Now, the design specifications of the mission will be completed and the costs will be evaluated. Finally, the mission will be proposed for “adoption” by ESA, followed by the construction of the spacecraft. The launch of the three satellites is scheduled for 2034. The science measurements of LISA would begin about one year after launch, and the science mission (https://www.elisascience.org) is planned to last at least 4 years and could be extended to last for as long as 10 years.
