Gravitational waves from space: new horizons for fundamental physics

From Einstein’s theory to the first detections

Gravitational waves (ripples in spacetime predicted by Einstein over a century ago) have revolutionized our understanding of the universe since their first detection in 2015 by the LIGO/VIRGO ground-based interferometers. This discovery opened a new window onto the cosmos, allowing us to observe previously inaccessible phenomena and investigate fundamental questions such as the nature of gravity, the origin of black holes, and the evolution of the universe.
Ground-based detectors, however, face an intrinsic limitation: terrestrial environmental noise obscures low-frequency gravitational wave sources (below about 1 Hz), such as supermassive black holes. To overcome this barrier, the scientific community is developing new technologies to detect these waves directly from space, where the environment is vastly more “quiet.”

The LISA Mission and the LPF Testbed

Within this framework arises LISA (Laser Interferometer Space Antenna), an ESA mission scheduled for launch in 2035. LISA will be the first space observatory dedicated to gravitational waves and will consist of three satellites orbiting the Sun in a triangular formation approximately 2.5 million km apart. Laser beams will link the satellites, measuring tiny variations in distance between freely falling test masses inside the spacecraft, variations caused by passing gravitational waves.
Given the technological complexity, ESA preceded LISA with a test mission: LISA Pathfinder (LPF), launched in 2015 and operational until 2017. The University of Trento played a key role, with Prof. Stefano Vitale as Principal Investigator, supported by Professors Daniele Bortoluzzi, William Weber, and Rita Dolesi.
The main goal of LPF was to demonstrate the ability to keep two test masses in free fall inside the satellite, isolating them from any external disturbance. The mission was an outstanding success: not only did it prove feasibility, but it achieved a precision in acceleration measurement ten times better than required.

Challenges of the Release Mechanism

Despite its success, some challenges emerged. In particular, the mechanism designed to lock the masses during launch and release them in orbit did not perform as expected: data showed linear and rotational velocities different from predictions in most releases.
It is precisely in this context that the present research fits, aiming to provide a clear and reliable understanding of LPF’s release mechanism dynamics. Fully understanding its behavior is crucial, as the same system will be used in LISA.
The work is divided into three main phases:

• Development of dynamic models — digital twins that reproduce the multiphysics behavior of the flight version of the release mechanism.
• Identification of critical phenomena influencing the release of the masses: surface adhesion between the mechanism and the test mass, and asymmetries in mechanism motion (velocity, timing delay).
• Development of an innovative technique to precisely measure the impulse due to adhesion, based on vibration analysis of the test mass. 

Statistical analysis of these factors showed that the probability of a compliant release is 99.99%, provided the anomalies observed in LPF are avoided. Some of the proposed modifications are already being implemented in a prototype developed in collaboration with OHB-Italia.
The work continues: in the coming months, intensive testing is planned to further optimize the mechanism and ensure its reliability, paving the way for one of the most ambitious missions ever undertaken in fundamental physics.

Focus Box 1 – What Are Gravitational Waves?

Gravitational waves are distortions of spacetime generated by extreme astrophysical events, such as the merging of black holes or neutron stars. Unlike light or electromagnetic waves, they are neither absorbed nor deflected by matter, thus carrying “pure” information about the events that created them. They represent a unique tool to observe the universe.

Focus Box 2 – Why Is LISA Different from LIGO?

LIGO (on Earth) measures distance variations as small as a thousandth of a proton’s diameter but is limited by seismic and environmental noise, observing only “fast” events lasting less than a second.
LISA, operating in space, will detect much lower frequencies corresponding to “slower,” larger-scale cosmic events (like mergers of supermassive black holes). The two instruments are not competitors but complementary: together, they allow exploration of the full gravitational-wave spectrum.

In the picture, from left to right: Daniele Bortoluzzi, Matteo Tomasi, Davide Vignotto, Abraham Ayele Gelan, Carlo Zanoni, Edoardo Dalla Ricca, Francesco Marzari. Not in the picture but part of the Team: Giuliano Agostini.