Space-based Gravitational-Wave Observatory LISA Gets Green Light

The science of studying gravitational waves got a big boost for the European Space Agency. Its science program team affectionately calls the Laser Interferometer Space Antenna LISA for official planning and building. That means gravitational wave astronomers will take their next steps to capture information about gravitational waves from space.

LISA – or something like it – has been on the drawing boards since the 1980s. The current LISA observatory was proposed a decade later and scientists flew a „Pathfinder mission” to test its primary design. Now, it's going to be a complete set of three spacecraft that will launch in 2035 and revolutionize gravitational wave studies.

This graphic shows how LISA will work. Courtesy ESA.

The spacecraft orbits the constellation in three separate phases in an Earth-like heliocentric orbit. Basically, they will form a triangle that will be linked together by laser beams that will each shoot 2.5 million kilometers into space. Those beams will be the primary gravitational wave detectors. As a wave passes through, it changes the length of each laser „arm”. Sophisticated instruments on board record changes and transmit that data back to Earth for analysis. Different changes in the length of each arm can tell scientists important information about the objects that collided to create the waves. If all goes well, LISA will become the first space-based observatory dedicated solely to these ripples in the fabric of spacetime.

Next steps

The decision to move forward with LISA is a formal step called „adoption”. It basically says that the technology and concept and timeline for the task is good to go. This allows the agency to develop the spacecraft and its instruments. From this point, the agency is now free to solicit and select contractors for fabrication. The design and assembly process could begin in January 2025.

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According to lead project scientist Nora Lutzgendorf, the development of LISA was not easy. „LISA is an initiative that has never been attempted before,” he said. „Using laser beams several kilometers away, ground-based instruments can detect gravitational waves from events involving stellar-sized objects — such as supernova explosions or superdense stars and supermassive black holes. We need to go into space to expand the scope of gravity probes. The great distances traveled by laser signals on LISA And thanks to the excellent stability of its instruments, we will study gravitational waves of lower frequencies than possible on Earth, discovering phenomena of different scales. Time.”

Protecting LISA from external impacts in space

Of course, space presents unique challenges to the mission of the spacecraft. In that sense, LISA faces some of the same problems that LIGO and others encounter on the ground. For example, ground noise from heavy trucks driving by could disturb the LIGO instruments. That means its scientists have to filter out non-gravitational-wave disturbances.

Fortunately there are no trucks in space, but LISA will encounter some non-gravitational tidal forces such as light pressure and the solar wind. Scientists will be around people with some very clever spacecraft designs. Each of the three craft will have telescopes, lasers and test masses made of gold and platinum coated with gold.

To protect the test masses from external impacts (which would push the masses „around”), they float freely inside the spacecraft. The craft's outer shells absorb external impacts. Thrusters fix the spacecraft in position and prevent the masses from experiencing anything but target gravitational waves. As a result, gravitational wave data from distant objects and events in the Universe should be captured more „cleanly.”

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LISA's Gravitational Wave Targets

This complex task can capture the ripples in spacetime created when massive objects collide. These include mergers of supermassive black holes at the heart of galaxies. In our own galaxy, LISA can detect mergers of white dwarfs or neutron stars. Its data should provide astronomers with precise information about the distances to these events and their locations.

Sources of Gravitational Waves in the Universe Detected by LISA.  Courtesy ESA.
Sources of Gravitational Waves in the Universe Detected by LISA. Courtesy ESA.

„For centuries we have studied our universe by capturing light. Combining this with the detection of gravitational waves brings an entirely new dimension to our view of the universe,” said LISA project scientist Oliver Jenrich. „Until now, with our astrophysical missions, we've seen the universe as a silent movie. Imagine capturing the ripples of spacetime with LISA would be a real game-changer, just like adding sound to motion pictures.”

An exciting possibility that LISA could enable is to detect the first seconds of the Big Bang. That's because gravitational waves from that sperm event carry information about distance and intensity. In addition, LISA data will help astronomers measure the expansion rate of the universe over time. If all of this comes to pass, it will prove the usefulness of gravitational waves as a unique way to measure things in the universe.

For more information

Capturing the ripples of spacetime: LISA advances
LISA Consortium

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