Capturing the vibrations of spacetime: LISA gets approval

Science & Exploration

25/01/2024
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Today, the Laser Interferometer Space Antenna (LISA) mission has been approved by ESA’s Science Programme Committee, marking the first scientific effort to detect and study gravitational waves from space.

The approval, known as ‘adoption’, acknowledges that the mission concept and technology are sufficiently advanced, and authorizes the construction of the instruments and spacecraft. This process will commence in January 2025, once a European industrial contractor has been selected. LISA consists of a constellation of three spacecraft. These will follow Earth in its orbit around the Sun, forming an incredibly precise equilateral triangle in space. Each side of the triangle will measure 2.5 million km in length (more than six times the Earth-Moon distance), and the spacecraft will exchange laser beams over this distance. The launch of the three spacecraft is scheduled for 2035, aboard an Ariane 6 rocket. Led by ESA, LISA is made possible through collaboration between ESA, its Member State space agencies, NASA, and an international consortium of scientists (the LISA consortium).

LISA – measuring gravitational waves

Bringing ‘sound’ to the cosmic movie

Just over a century ago, Einstein made the groundbreaking prediction that massive objects, when they accelerate, disturb the fabric of spacetime, producing minuscule ripples known as gravitational waves. Thanks to modern technological advancements, we are now capable of detecting these highly elusive signals. “LISA is an endeavor that has never been attempted before. By using laser beams over distances of several kilometers, ground-based instrumentation can detect gravitational waves originating from events involving star-sized objects, such as supernova explosions or the merging of hyper-dense stars and stellar-mass black holes. To push the boundaries of gravitational studies, we must venture into space,” explains LISA lead project scientist Nora Lützgendorf. “Thanks to the extensive distance covered by the laser signals on LISA, and the exceptional stability of its instrumentation, we will explore gravitational waves of lower frequencies than what is possible on Earth, uncovering events of a different scale, all the way back to the beginning of time.”

The spectrum of gravitational waves

LISA will detect, across the entire Universe, the ripples in spacetime caused by massive black holes colliding at the centers of galaxies. This will allow scientists to trace the origin of these massive objects, understand how they grow to be millions of times more massive than the Sun, and establish the role they play in the evolution of galaxies. The mission is poised to capture the predicted gravitational ‘ringing’ from the initial moments of our Universe and offer a direct glimpse into the first seconds after the Big Bang. Additionally, because gravitational waves carry information about the distance of the objects that emitted them, LISA will help researchers measure the change in the expansion of the Universe using a different method from the techniques employed by Euclid and other surveys, thereby validating their results. Closer to home, within our galaxy, LISA will detect many merging pairs of compact objects, such as white dwarfs or neutron stars, and provide a unique insight into the final stages of the evolution of these systems. By pinpointing their positions and distances, LISA will enhance our understanding of the structure of the Milky Way, building upon the findings from ESA’s Gaia mission. “For centuries, we have been studying our cosmos through capturing light. Combining this with the detection of gravitational waves introduces an entirely new dimension to our perception of the Universe,” remarks LISA project scientist Oliver Jennrich. “If we imagine that, so far, with our astrophysics missions, we have been observing the cosmos like a silent movie, capturing the ripples of spacetime with LISA will be a real game-changer, akin to when sound was added to motion pictures.”

Golden cubes and laser beams

Golden cubes for LISA

In order to detect gravitational waves, LISA will utilize pairs of solid gold-platinum cubes, known as test masses (slightly smaller than Rubik’s cubes), which will be free-floating in special housing at the heart of each spacecraft. Gravitational waves will cause minute changes in the distances between the masses in the different spacecraft, and the mission will track these variations using laser interferometry. This technique involves directing laser beams from one spacecraft to the other and then superimposing their signals to determine changes in the distances between the masses down to a few billionths of a millimeter. The spacecraft must be designed to ensure that nothing, besides the geometry of spacetime itself, affects the movement of the masses, which are in freefall.

Solid heritage and future teamwork

The spacecraft follows in the footsteps of LISA Pathfinder, which demonstrated that it is possible to maintain the test masses in freefall with an astonishing level of precision. The same precision propulsion system that has also been utilized in ESA’s Gaia and Euclid missions will ensure that each spacecraft maintains the required position and orientation with the highest accuracy. Selected as the third large mission of ESA’s Cosmic Vision 2015–2025, LISA will join ESA’s science fleet of cosmic observers to address two fundamental questions at the core of the program: What are the fundamental physical laws of the Universe? How did the Universe originate, and what is it made of? In this pursuit, LISA will collaborate with ESA’s other large mission currently under study: NewAthena. Set to be the largest X-ray observatory ever built, NewAthena is expected to launch in 2037. Notes for editorsESA leads the LISA mission and will provide the spacecraft, launch, mission operations, and data handling. Key instrumental elements include the free-falling test masses shielded from external forces, provided by Italy and Switzerland; the picometer-accuracy systems to detect the interferometric signal, provided by Germany, the UK, France, the Netherlands, Belgium, Poland, and the Czech Republic; and the Science Diagnostics Subsystem (an arsenal of sensors across the spacecraft), provided by Spain. The ultra-stable lasers, the 30 cm telescopes to collect their light, and the sources of UV light (to discharge the test masses) will be provided by NASA. For more information, please contact: ESA Media Relations
Email: media@esa.int

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