|Cosmic Vision Themes||The Gravitational Universe|
|Primary goals||Observing low-frequency gravitational waves (from 0.1 mHz to 0.1 Hz) and studying their various sources from across the cosmos|
|Orbit||Three spacecraft in an Earth-trailing heliocentric orbit about 50 million km from Earth (inter-spacecraft separation of 2.5 million km)|
|Lifetime||Four years, with possible six-year extension|
LISA – the Laser Interferometer Space Antenna – will be the first dedicated space-based gravitational wave observatory. Gravitational waves are ripples in the fabric space-time created by suitably accelerated objects, such as pairs of black holes coming together and merging. LISA will be the first mission probing the entire history of the Universe using gravitational waves.
The mission will comprise three spacecraft flying in a triangular formation behind the Earth as our planet orbits the Sun. The separation of free-floating reference surfaces in each satellite is measured precisely using laser interferometry over the 2.5 million km long 'arms', in order to detect and measure minuscule variations caused by a passing gravitational wave.
LISA will aim to tackle a number of key themes under the Cosmic Vision science theme of 'The Gravitational Universe'. As part of its core science objectives, it will:
- Study the formation and evolution of compact binary stars in the Milky Way galaxy;
- Trace the origin, growth and merger history of massive black holes across cosmic ages;
- Probe the dynamics of dense nuclear clusters using extreme mass-ratio inspirals (EMRIs);
- Understand the astrophysics of stellar-origin black holes;
- Explore the fundamental nature of gravity and black holes;
- Probe the rate of expansion of the Universe;
- Understand stochastic gravitational wave backgrounds and their implications for the early Universe and TeV-scale particle physics;
- Search for gravitational wave bursts and unforeseen sources.
LISA will study the very nature of gravity itself by exploring the waves that emanate from some of the most massive and extreme phenomena in the Universe. While high-frequency gravitational waves from the mergers of stellar-mass black holes and neutron stars have been detected from Earth – using experiments such as the US-based Laser Interferometer Gravitational-Wave Observatory (LIGO) and the European Virgo observatory – LISA will detect low-frequency gravitational waves, enabling scientists to probe different classes of sources, including the mergers of supermassive black holes at the cores of massive galaxies.
The observatory scans the entire sky from space continuousyl and, as it follows the Earth in its orbit, gradually improves the localisation of the gravitational wave sources it detects. It will observe the dynamic cosmos from the smallest to the very largest scales, and expand our cosmic horizon back to the cosmic epochs preceding the formation of stars and galaxies, mapping the build-up of structure during the first hundred million years of the history of the Universe.
In 2013, ESA selected 'The Gravitational Universe' as the theme for the third large-class mission, L3, to be developed under ESA's Cosmic Vision science planning cycle, with launch scheduled for the early 2030s. On 20 June 2017, ESA's Science Programme Committee chose LISA as the L3 mission. LISA has since entered a more detailed phase of study and will be proposed for 'adoption' around 2023 before the construction phase begins.