Green Light for LISA

The LISA (Laser Interferometer Space Antenna) mission to investigate gravitational waves in space has successfully completed the preliminary studies and testing phase. During this phase, the entire concept - from the technical specifications of the scientific instruments and operating system to the devices that will need to be built for use in space - was carefully scrutinized by experts as part of the Mission Adoption Review. On 25 January, following the review, the Science Programme Committee of the ESA (European Space Agency) officially confirmed that the technology is mature enough to continue developing the mission as planned. In other words, the mission got the “green light” to go ahead. The space antenna, which will be used to observe gravitational waves in space and thus detect collisions of supermassive black holes, for example, will be launched around 2035.

More than 120 research institutions across Europe and the United States are involved in the LISA mission, including the ETH Zurich and University of Zurich (UZH). Philippe Jetzer, professor of gravitation and astrophysics at the University of Zurich, and Domenico Giardini, professor of seismology and geodynamics at ETH Zurich, have been closely cooperating on the project for more than two decades. In this interview, the professors outline the expectations for the mission and explain the involvement of the two Swiss universities in Zurich.

The LISA mission has been given the go-ahead! What does this mean for space research?
Domenico Giardini: A lot! We must remember that 95 percent of our universe is still regarded as dark energy or dark matter because it emits no electromagnetic waves, remaining invisible to all our telescopes. Gravitational waves will allow us to investigate this invisible universe. All that Ligo-Virgo observed was the final collapse of stellar black holes with a duration of less than one second. This was due to major background seismic noise on Earth and the fact that instruments with maximum arm lengths of four kilometres can only measure higher frequencies. LISA will overcome these limitations: there is no seismic noise in space, and LISA can register much lower frequencies thanks to an arm length of 2.5 million kilometres. This will make the detection of the collapse of supermassive black holes possible as well as countless close galactic binary star systems – not to mention a vast number of dynamic objects and phenomena that will help us understand how the universe was formed and how it continues to evolve.

Philippe Jetzer: This launch is the result of several decades of work spent on maturing the technology needed to build this gigantic space antenna. LISA will provide us with a new view of the universe. We hope to gain new insights into its origins and development – such as how the Big Bang came about. Perhaps, we will also find out whether Einstein’s theory of relativity is valid across the board, or whether there are any deviations that would give us new insights into the fundamental laws of physics.

How are ETH Zurich and UZH involved in this mission?
Domenico Giardini: ETH Zurich plays a central role in LISA. Working together with Swiss industry and with the support of the Swiss Space Office, we are supplying the front-end electronics for the gravitational reference sensor, the heart of the LISA measurement system. This sensor enables the spacecraft to follow the reference mass. We are also participating in ESA’s Performance and Operation Team, building the Swiss node of the Distributed Data Processing Centre. Together with other European and American nodes, this node processes all the data sent by LISA, builds global models of our universe and identifies the catalogue of gravitational wave sources. I am a member of the LISA Executive Committee and the LISA Consortium Board.

Philippe Jetzer: In my working group, we have focused on investigating the possible sources of gravitational waves that LISA could observe. With the help of Einstein’s theory of general relativity, we have calculated various expected forms of gravitational waves. These different models will be needed at a later date to enable LISA’s data to be analysed a lot more precisely. Our calculations are therefore of great importance for the precise planning of the mission and thereafter. I have been a member of ESA’s LISA Science Working Team for many years, as well as a member of the LISA Consortium Board.

What does the research team plan to work on next?
Domenico Giardini: In addition to activities related to the delivery of the electronics and the construction of the Swiss data centre, our research will focus on developing better global models and pipelines for data analysis and the identification of gravitational wave sources. This will enable us to create a digital twin of our universe in close collaboration with the University of Zurich and other ESA and NASA nodes.

Philippe Jetzer: Following my co-authoring of the Red Book – a detailed summary of the scientific objectives and technical aspects of the LISA mission – we will start calculating ever better models of gravitational waves and working on other observations that could be made possible by LISA. These are very complicated calculations that can be continuously improved. These studies will continue for several years – certainly until the satellites are launched and the data is analysed.

The antenna will be launched into space in 2035. What other hurdles does the project still have to overcome?
Domenico Giardini: One challenge will be to complete the antennas on time. Three identical satellites will need to be built that send each other signals in a triangle formation with the utmost accuracy and over huge distances. Given the shortage of experts in industry and academia, we need to plan the necessary processes very precisely. As far as I know, the team does not anticipate any insurmountable technical challenges. Some highly detailed studies have been carried out, and we can draw on our experience with the very successful LISA Pathfinder test satellite, in which we were also involved.

How does it feel to be involved in such a prestigious and lengthy project – even if you probably won’t be able to play an active role at the time of its launch?
Domenico Giardini: LISA will run for more than 50 years, and three generations of scientists will be working to make the mission a success. We are obviously delighted to have the privilege of playing a central role in this mission. In 2015 we witnessed the fantastic launch of LISA Pathfinder live.

Philippe Jetzer: We won’t be there in person when the LISA satellites are launched in 2035. But we are confident that we will be able to help with the next, very intensive preparation phase and with the initial analysis of the data. Some of our former and current doctoral students and postdoctoral researchers are still involved in LISA’s preparation and are very active in the field of gravitational wave research. Two new professorships will also be established at ETH Zurich and the University of Zurich. Other colleagues from ETH and UZH are already involved or are interested in participating at a later stage.