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Author: Joffrey Rieger

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Remembering Astrophysicist Peter Bender

Credit: Steven Burrows, JILA

It is with great sorrow that we have learnt that Pete Bender, at the age of 93, passed away last Saturday, 22 April 2024.

LISA, as we know it today, has for a large part its origin in Pete’s creativity, deep physical insight and intellectual rigor.
It is a small consolation that he could witness the final approval of the mission by the European Space Agency last January.

Pete has been a guide and a model for many of us in the LISA community, and his legacy and example will continue to drive our effort toward the success of the LISA mission.

Read the Obituary on the JILA Website
You could also add something to the Memorial Page

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LISA Waveforms White Paper

LISA, the Laser Interferometer Space Antenna, will usher in a new era in gravitational-wave astronomy. As the first anticipated space-based gravitational-wave detector, it will expand our view to the millihertz gravitational-wave sky, where a spectacular variety of interesting new sources abound: from millions of ultra-compact binaries in our Galaxy, to mergers of massive black holes at cosmological distances; from the beginnings of inspirals that will venture into the ground-based detectors’ view to the death spiral of compact objects into massive black holes, and many sources in between. Central to realising LISA’s discovery potential are waveform models, the theoretical and phenomenological predictions of the pattern of gravitational waves that these sources emit. This white paper is presented on behalf of the Waveform Working Group for the LISA Consortium. It provides a review of the current state of waveform models for LISA sources, and describes the significant challenges that must yet be overcome.

Link on Springer.com

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LISA Fundamental Physics White Paper

The Laser Interferometer Space Antenna (LISA) has the potential to reveal wonders about the fundamental theory of nature at play in the extreme gravity regime, where the gravitational interaction is both strong and dynamical. In this white paper, the Fundamental Physics Working Group of the LISA Consortium summarizes the current topics in fundamental physics where LISA observations of gravitational waves can be expected to provide key input. We provide the briefest of reviews to then delineate avenues for future research directions and to discuss connections between this working group, other working groups and the consortium work package teams. These connections must be developed for LISA to live up to its science potential in these areas.

Link on Springer.com

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LISA Cosmology White Paper

The Laser Interferometer Space Antenna (LISA) has two scientific objectives of cosmological focus: to probe the expansion rate of the universe, and to understand stochastic gravitational-wave backgrounds and their implications for early universe and particle physics, from the MeV to the Planck scale. However, the range of potential cosmological applications of gravitational-wave observations extends well beyond these two objectives. This publication presents a summary of the state of the art in LISA cosmology, theory and methods, and identifies new opportunities to use gravitational-wave observations by LISA to probe the universe.

Link on Springer.com

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LISA Astrophysics White Paper

The Laser Interferometer Space Antenna (LISA) will be a transformative experiment for gravitational wave astronomy, and, as such, it will offer unique opportunities to address many key astrophysical questions in a completely novel way. The synergy with ground-based and space-born instruments in the electromagnetic domain, by enabling multi-messenger observations, will add further to the discovery potential of LISA. The next decade is crucial to prepare the astrophysical community for LISA’s first observations. This review outlines the extensive landscape of astrophysical theory, numerical simulations, and astronomical observations that are instrumental for modeling and interpreting the upcoming LISA datastream. To this aim, the current knowledge in three main source classes for LISA is reviewed; ultra-compact stellar-mass binaries, massive black hole binaries, and extreme or interme-diate mass ratio inspirals. The relevant astrophysical processes and the established modeling techniques are summarized. Likewise, open issues and gaps in our understanding of these sources are highlighted, along with an indication of how LISA could help making progress in the different areas. New research avenues that LISA itself, or its joint exploitation with upcoming studies in the electromagnetic domain, will enable, are also illustrated. Improvements in modeling and analysis approaches, such as the combination of numerical simulations and modern data science techniques, are discussed. This review is intended to be a starting point for using LISA as a new discovery tool for understanding our Universe.

Link to the Astrophysics White Paper on Springer.com

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LISA’s Orbit

LISA will consist of three spacecraft separated by 2.5 million km in a triangular formation, following Earth about 50 million km in its orbit around the Sun.

The observatory scans the entire sky from space continuously and, as it follows the Earth in its orbit, gradually improves the localization of the gravitational wave sources it detects.

The LISA Orbit

The proposed orbit for LISA is an Earth-trailing heliocentric orbit between 50 and 65 million km from Earth,

The angles in the LISA orbit

The orbit has been optimised to minimise the key variable parameters of the separation between the scienecraft, breathing angles (fluctuations of vertex angles) and the range rate of the sciencecraft, as both of these drive the complexity of the payload design, while at the same time ensuring the range to the constellation is sufficiently close for communication purposes.


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The payload

The core features of the payload have been stable for more than a decade: the interferometric measurement system, the telescope, the gravitational reference sensor. Their design has evolved and reached maturity. Many of the design features and concepts of LISA, e.g., the optical bench, have been demonstrated on LISA Pathfinder (LPF).

LISA is designed to measure gravitational radiation over a broad band at low frequencies, from about 0.1 mHz to 1 Hz, a band where the Universe is richly populated by strong sources of gravitational waves.

LISA can achieve 10-20 strain resolution by measuring displacements of the order of a picometer. Its observations in the quiet environment of space will not be disturbed by seismic and gravity-gradient noise. Thus, LISA’s unparalleled sensitivity will allow studying sources within the Galaxy and out to the edge of the visible Universe.

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More on Sciencecraft

The classical distinction between spacecraft and payload doesn’t fit LISA well, because the LISA spacecraft are not just providing the infrastructure for the instruments. Each LISA spacecraft is part of the instrument itself because it protects the free-falling test masses from disturbances. The LISA spacecraft must thus be designed and built with the gravitational requirements of the free-falling test masses in mind.

The usual structural and thermal analysis of the spacecraft has therefore been extended to include gravitational effects as well to ensure that the requirements on gravity gradient at the position of the test masses is fully met. In addition, the payload controls the position of the spacecraft during science operations, rendering the spacecraft effectively a part of the instrument. The importance of the co-design and the co-operation of spacecraft and payload is captured in the term “sciencecraft”.

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Exotic Sources

Studying gravitational waves has enormous potential for discovering those parts of the Universe that are not yet observed such as the gravitational repercussions from the Big Bang, the ripples of spacetime emerging from perturbations of the primaeval plasma, and other, as yet unknown, objects. Working in conjunction with other astronomical methods and gravitational-wave observatories on Earth, LISA scientists will contribute to the next big discoveries to answer questions such as “What are the fundamental laws of the Universe?” and “How did the Universe originate and what is it made of?