The future Lisa space observatory has cleared crucial hurdles to its realization. The satellite project to observe gravitational waves in space is now entering the next phase of its implementation.
According to the Lisa consortium, the European space agency Esa as the lead agency and the US space agency Nasa, it is now well on the way to starting in the mid-2030s. The Max Planck Institute for Gravitational Physics (Albert Einstein Institute/AEI) in Hanover and Potsdam also plays a central role in the project. An international symposium on Lisa is taking place this week.
The Albert Einstein Institute was also instrumental in the first measurement of a gravitational wave on September 14, 2015. 100 years after Albert Einstein predicted their existence, and after decades of painstaking searching, these minute changes in space-time had been directly detected for the first time.
The scientific breakthrough at that time was achieved with ground-based detectors, since then such gravitational waves from the depths of the universe have been measured repeatedly. They are caused by systems of accelerated mass such as binary star systems, planets orbiting a star, but also by the collision of large masses, such as two black holes.
The goal of the Lisa mission is now to be able to measure these waves directly in space, free from interference on Earth. The waves provide researchers with signals from the early days of the universe. In this way they hope to get a much better picture of the origin of the world. They also speak of a new window on the universe.
Revolutionary scientific results are expected. Researchers also hope to be able to look further back than previously possible to the beginning of the universe. The consortium speaks of an unprecedented view of the universe.
Measurements of gravitational waves provide the researchers with a wealth of information that was not previously available: “The measured signals make it possible for the first time to observe merging black holes and neutron stars and thus to deduce their properties,” says AEI researcher Alessandra Buonanno.
The Lisa observatory in space will consist of three satellites flying in a triangular constellation, forming a detector with laser arms 2.5 million kilometers long. The satellites will follow Earth as it orbits the Sun and will observe gravitational waves from sources across the Universe.
The satellite observatory differs fundamentally from other space telescopes. Electromagnetic waves are not measured, but the changes in space-time caused by gravitational waves.
Gravitational waves stretch and compress the space-time continuum. In the millions of kilometers spanning laser triangle between the three Lisa satellites, they produce minimal changes in distance as they pass – smaller than the diameter of an atom.
Lisa’s detectors will detect these tiny shifts to measure gravity waves. Free-fall test masses are positioned inside the three satellites. Lisa’s laser detectors constantly monitor them, changing their position when a gravitational wave passes – the wave is measured.
“When the scientific results are combined with the observations of other ground-based and space-based observatories, enormous advances in multi-messenger astronomy can be achieved,” according to the Lisa consortium. The observatory will measure the gravitational waves in a lower frequency band than the ground-based detectors Ligo and Virgo: “This will enable the mission to observe much larger systems and events that occurred far back in time in the early days of our universe.”
The technology and plans for the project were recently reviewed by the US National Academy of Sciences. Esa, Nasa, scientists and business have now given the green light for the next development phase. The project has thus passed a crucial checkpoint and is now moving from the concept study phase to the implementation process.
A test in space had already taken place with the Lisa Pathfinder mission in 2015 and showed that Lisa met the required measurement technology and all requirements – and was ready to fly.
Karsten Danzmann, head of the Lisa consortium, now sees the project on the home stretch after the evaluations: “We are now developing all the details of Lisa and specifying the full requirements and the review strategy.” Martin Gehler, Lisa study leader at Esa, sees it the past review as a great success for all concerned.
