Laser Interferometer Space Antenna (1702.00786v3)

Abstract: Following the selection of The Gravitational Universe by ESA, and the successful flight of LISA Pathfinder, the LISA Consortium now proposes a 4 year mission in response to ESA's call for missions for L3. The observatory will be based on three arms with six active laser links, between three identical spacecraft in a triangular formation separated by 2.5 million km. LISA is an all-sky monitor and will offer a wide view of a dynamic cosmos using Gravitational Waves as new and unique messengers to unveil The Gravitational Universe. It provides the closest ever view of the infant Universe at TeV energy scales, has known sources in the form of verification binaries in the Milky Way, and can probe the entire Universe, from its smallest scales near the horizons of black holes, all the way to cosmological scales. The LISA mission will scan the entire sky as it follows behind the Earth in its orbit, obtaining both polarisations of the Gravitational Waves simultaneously, and will measure source parameters with astrophysically relevant sensitivity in a band from below $10^{-4}\,$Hz to above $10^{-1}\,$Hz.

• The paper presents LISA’s groundbreaking proposal for detecting low-frequency gravitational waves from diverse cosmic sources using a triad of spacecraft.
• The paper details innovative techniques like laser interferometry, drag-free control, and micropropulsion to ensure precise measurements across vast distances.
• The paper highlights LISA’s potential to elucidate binary star evolution, trace massive black hole mergers, and test the limits of General Relativity.

Overview of the Laser Interferometer Space Antenna Proposal

The Laser Interferometer Space Antenna (LISA) project, proposed as a response to the European Space Agency (ESA) call for L3 mission concepts, aims to explore new frontiers in gravitational wave astronomy. This space-based observatory will detect and paper gravitational waves (GWs) across a range of cosmological sources, focusing significantly on low-frequency GWs, which are inaccessible to ground-based detectors. LISA is positioned to substantially advance our current understanding of the universe's structure and evolution by harnessing the unique capabilities of GWs.

Mission Goals and Scientific Objectives

LISA is designed to survey the universe with unparalleled GW sensitivity, investigating the following core scientific objectives:

• Formation and Evolution of Binary Stars: LISA will elucidate the dynamics of compact binary stars within the Milky Way, enabling precision measurements of their orbital periods, masses, and spatial distributions. This includes detecting up to 25,000 individual Galactic Binaries, predominantly composed of white dwarfs, neutron stars, and stellar-origin black holes.
• Massive Black Hole Merger Histories: The mission will trace the origins and evolution of Massive Black Holes (MBHs) across cosmic ages, observing black hole mergers from redshifts up to ~15. This will shed light on the relationship between MBH formation and galaxy development.
• Dynamics of Nuclear Clusters and EMRIs: LISA aims to reveal Extreme Mass Ratio Inspirals (EMRIs), the orbital behaviors of stellar-origin black holes around MBHs, deciphering the spacetime dynamics at galaxy centers.
• Astrophysics of Stellar-Origin Black Holes: By enabling multi-band and multi-messenger observations of black hole mergers, LISA will probe the environments and formation channels of stellar-origin black holes.
• Fundamental Nature of Gravity and Black Holes: The mission will test the nature of gravity in strong-field regimes and explore the validity of General Relativity (GR). This includes probing into beyond-GR physics and detecting deviations from expected GW propagation properties.
• Rate of Universe Expansion: LISA will contribute to measurements of cosmic expansion parameters using GW standards across various sources, potentially reconciling discrepancies in current measurements.
• Stochastic GW Background and Cosmology: LISA aims to detect and characterize stochastic GW backgrounds, providing insights into early universe physics and TeV-scale particle phenomena.

Mission Profile and Technological Framework

LISA's scientific capabilities pivot on a space-based system featuring three identical spacecraft forming a triangular constellation in an Earth-trailing heliocentric orbit. Each spacecraft houses laser interferometers of high precision, capable of measuring minute disruptions in spacetime caused by GWs. The system optimizes the detection of low-frequency GWs (0.1 to 100 mHz), which correspond to the colossal cosmic phenomena unseen by terrestrial observatories.

Critical to LISA's operation are technologies like drag-free control systems, micropropulsion units, and extremely stable optical components—many elements of which derive directly from the successes and findings of the LISA Pathfinder mission. The mission plans are bolstered by a robust architecture for data communication and ground-based processing, ensuring continuous observation with minimal latency.

Challenges and Implications

While the concept builds on proven technologies, LISA faces challenges related to long-term stability and complex mission operations—particular attention to thermal control, scattered light mitigation, and precise timing synchronization across its spacecraft. Nonetheless, the collective expertise from multiple international teams provides the foundation to address these challenges effectively.

LISA's ability to explore cosmic phenomena will impact both theoretical frameworks and practical applications. It will refine models of cosmological evolution, test the limits of physical theories, and potentially uncover new particle physics phenomena. Its findings could catalyze innovations in both astrophysics and broader scientific disciplines by revealing unseen dynamics of the universe.

Future Prospects

As LISA progresses toward potential implementation and deployment, this mission promises to be a cornerstone in gravitational wave astronomy, expanding the boundaries of our knowledge and offering profound insights into the universe's deepest mysteries. The harmonious collaboration between ESA, NASA, and international scientific entities underscores its potential for tremendous scientific impact and successes.