The LISA experiment is a space-mediated gravitational wave detector aimed at measuring waves from large-scale celestial events, which enhances understanding of the universe by capturing signals that terrestrial observatory such as Ligo and Virgo cannot detect.
Gravitational waves have emerged as one of the most exciting frontiers in modern astrophysics, reconstructing our understanding of the universe and fundamental forces during play. These ripples in the fabric of space-time were first predicted by Albert Einstein more than a century ago, and have invaluable information about some of the most intense events in our universe, such as the fusion of black holes and neutron stars.
The laser interferometer Gravitational Wave Observatory (LIGO) and its European counterpart Virgo marked a historic milestone in 2015 when it first successfully detected gravitational waves. These terrestrial facilities offer deep insight into the nature of black holes, the evolution of stars, the dynamics of the universe, and astronomical events that were previously invisible.
Despite its groundbreaking achievements, Ligo and Virgo operate over a limited frequency range and focus primarily on events that involve small black holes. This is where the laser interferometer space antenna (LISA) comes out.
The Innovation Platform spoke with Oliver Genrich, Head of Astrophysics at the European Space Agency, and Filippo Mariani, project manager at Lisa, to explore the complexity of the Lisa mission, its purpose, and the potential for transformations it holds for an understanding of the universe.
Can you explain the LISA experiment and its main purpose?
Lisa is a space-mediated gravitational wave detector. Gravitational waves in the frequency range of 0.1 MHz to 1 Hz are measured by recording the phase changes of laser beams transmitted between three satellites 2.5 million km apart. The main causes of gravitational waves in this frequency range are:
A huge black hole, a compact binary system of the Milky Way, as often found in the center of a galaxy, that is, both stars fall into the giant black hoin in the center of a galaxy, such as a white dwarves, neutron stars, or small compact objects such as small black holes (neutron stars, black holes).
Can we discuss the nature of gravitational waves, how they are generated, and their importance to our understanding of the universe?
Gravitational waves are “space-time ripples,” small disturbances in space-time that propagate at the speed of light and are generated as an object accelerates. Gravitational waves are so weak that a huge mass (at least several times the mass of the sun) is required to produce gravitational waves that can be detected with current technology. Unlike light (or common electromagnetic radiation), they are transverse waves and have two polarized light. In contrast to electromagnetic radiation, they do not act on charge, they are not mass, not dipole waves, but quadrupole waves, leading to the “squash and aperture” of the mass ensemble.
Gravitational waves are a great tool for observing the universe. Because they essentially do not suffer from dust absorption, they can have a very clear view of their origins, even at very long distances, until the time when the first galaxies were formed.
It also provides an alternative view of the objects to observe in the electromagnetic spectrum, allowing us to better understand the history of the universe, how the larger structures we observe today were formed, and how the universe expands.
How does the LISA experiment increase our current understanding of gravitational waves compared to ground observatory observatory such as Ligo and Virgo?
LISA targets a different frequency range than ground-based detectors. The source of this Lisa is generally more maasib than Ligo, as the signal’s wavelength is proportional to the mass of the source. If Ligo is targeting objects with a solar mass of several to about 100, Lisa will observe objects up to a solar mass of one million. This allows you to address a variety of questions about the universe and “see” it even further back in time.
There is a small overlap between the source of the LISA and the ground-based detector. At the high frequency edge of LISA sensitivity (~1 Hz), we can observe a binary system that enters the Ligo/virgo sensitivity band over the next few weeks and months. For these sources, LISA acts as a “pre-warning” system for ground-based detectors, allowing for much more targeted searches in the data stream.
What challenges does Lisa Mission face from a technology and implementation perspective?
In a very simplified, very high-level method, there are two main challenges. It is to detect very small changes in the laser phase (~10^-5 of wavelength or picometer 10 seconds) and make sure those changes are caused by gravitational waves rather than instrument noise.
The former requires that the laser beam be exchanged between the satellites with sufficient light received by each other satellite (the laser beam extends to several kilometers in diameter over a distance of 2.5 million km). This measurement principle (interference) is well established on the ground, for example, in Rigo and Virgo, but receiving a relatively small amount of laser light (several hundred pw) aims to aim for distances (and hits them) other satellites makes this a difficult task.
The latter challenge is the core of the spacecraft’s ability to separate the position from external forces as much as possible, so that its position is determined solely by gravity, and is not affected by, for example, solar radiation pressure, interplanetary magnetic fields, and residual particles. This technology has been demonstrated by the LISA Pathfinder mission from 2015 to 2017, indicating that the effects of non-gravity forces can be kept at the minimum required for the test muse.
More specifically, Lisa’s satellite is an essential part of the measurement chain. The distribution of the masses (and changes in this distribution) must be known with high accuracy so that it can compensate for the pull of the masses’ spaceships.
Can you explain in detail the role of the European Space Agency in the development of LISA experiments?
ESA is the main mission agency, offering spacecraft, launchers and general mission architectures. The critical parts of the instrument and data analysis efforts will be provided by ESA member states, and NASA, as an international partner, will provide stretching, lasers, and systems that control the charge of the test mass. NASA also contributes to its data analytics efforts.
What is the timeline for ESA’s LISA missions? Also, what are the important milestones to look for before launching in the mid-2030s?
Industrial activities began in January 2025. The first two years will focus on the integration of spacecraft designs, which lead to the system preliminary design review planned for the fourth quarter of 2026 and the accumulation of an industrial consortium involving more than 50 European industries. The major project milestones are thermal and mechanical testing planned from mid-2028 to early 2029. In the final quarter of 2030, a critical design review confirms the goodness of the system design, including test activities performed in the initial development model.
At the beginning of 2031, the payload’s first flight hardware will be delivered to major contractors, and therefore will begin consolidation of the first spacecraft that will end at the same year. The first spacecraft’s environmental campaign will account for the first few months of 2032, with the second and third spacecraft being assembled and tested in a phenomenal way in 2032, 2033 and 2034.
How do you think Lisa will impact future scientific research and collaboration on a global scale? What scientific discoveries and breakthroughs can arise from the successful operation of LISA?
As far as massive space science missions go, the international collaboration of the scientific community and the size and composition of the scientific community is not uncommon. Globally, NASA has partnered with ESA on many missions (and vice versa), so Lisa isn’t that unusual either. So, Lisa ensures that global collaboration and teamwork can be achieved. This is a unique mission with unprecedented scale and sensitivity.
The most exciting scientific discoveries are unexpected discoveries. They hope to identify binary systems for thousands of galaxies in the galaxy, many of which are obscure in the electromagnetic spectrum. “See” an object merger for the first time is a million times larger than our Sun. The signals of these mergers can be compared with calculations of the general theory of relativity and once again tested Einstein’s famous theory. We can examine physics at the heart of the galaxy by observing the end mise of a small object falling into a central black hole. And we might even be able to detect echoes of the big bang.
This article will also be featured in the 22nd edition of Quarterly Publication.
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