A Horizon Study for Cosmic Explorer: Science, Observatories, and Community (2109.09882v2)

Abstract: This Horizon Study describes a next-generation ground-based gravitational-wave observatory: Cosmic Explorer. With ten times the sensitivity of Advanced LIGO, Cosmic Explorer will push gravitational-wave astronomy towards the edge of the observable universe ($z \sim 100$). The goals of this Horizon Study are to describe and evaluate design concepts for Cosmic Explorer; to plan for the United States' leadership in gravitational-wave astronomy; and to envisage the role of Cosmic Explorer in the international effort to build a "Third-Generation" (3G) observatory network that will make discoveries transformative across astronomy, physics, and cosmology.

• The paper introduces Cosmic Explorer, a 40 km interferometer designed to achieve ten times the sensitivity of Advanced LIGO and map cosmic evolution up to redshift 100.
• It details advanced optical technologies and upgraded instrumentation, such as frequency-dependent squeezed light and cryogenic silicon mirrors, to reduce noise and enhance detection precision.
• It emphasizes community engagement and international collaboration, integrating stakeholder input and cultural considerations into its comprehensive project design.

Cosmic Explorer: A Horizon Study

The Cosmic Explorer (CE) project represents a significant advancement in the field of gravitational-wave astronomy, proposing a next-generation ground-based observatory with the potential to revolutionize our understanding of the universe. This Horizon Study explores the scientific objectives, technical designs, and community engagement necessary to realize CE.

Scientific Objectives and Potential

Cosmic Explorer aims to push the boundaries of gravitational-wave detection with a 40 km-long interferometer offering ten times the sensitivity of Advanced LIGO. This increase in sensitivity will expand the observable universe, allowing detection of gravitational waves from sources previously unreachable, such as the first black holes formed in the universe and mergers at the edge of the observable universe. CE's scientific goals are organized into key themes:

1. Black Holes and Neutron Stars Throughout Cosmic Time: CE will enhance our understanding of black hole formation and evolution, from the remnants of Population III stars to supermassive black hole seeds in the early universe. With a redshift reach of $z \sim 100$, CE will map compact object populations over cosmic history, providing insights into the first stars and subsequent galaxy formation.
2. Dynamics of Dense Matter: The paper of neutron star mergers offers a unique window into the physics of dense matter. CE will provide precision measurements of neutron star properties, elucidating the equation of state and possible phase transitions in dense nuclear matter. Observations of post-merger phases will enable exploration of quantum chromodynamics under extreme conditions.
3. Extreme Gravity and Fundamental Physics: CE will probe the most intense gravitation conditions in the universe, testing general relativity with unprecedented detail. It will offer the potential to uncover physics beyond current models through observations of rare and novel compact objects, and it will explore the effects of dark matter and dark energy on gravitational-wave signals.

Design and Technology

The reference design for CE is a dual-recycled Fabry--Pérot Michelson interferometer, scaled up to 40 km arm lengths. The design employs advanced optical technologies developed for LIGO, including large, high-reflectivity optics and frequency-dependent squeezed light for quantum noise reduction. Planned upgrades will leverage evolving technologies, such as cryogenic silicon mirrors and 2 µm lasers, potentially further increasing sensitivity beyond the initial target.

Key technological challenges include developing low-loss optical coatings and handling technical noise sources like scattered light. The need for ultra-high vacuum systems to minimize residual gas noise is emphasized, with research ongoing to reduce construction costs through innovations like mild-steel beamtubes and coating alternatives.

Community Engagement and Collaboration

CE's success depends on strong community and stakeholder engagement. This includes building relationships with Indigenous communities, local stakeholders, and the broader scientific community. Ensuring that CE respects the cultural and environmental contexts of potential sites is paramount. The project is committed to integrating community input at all stages, fostering educational outreach, and forming international partnerships to develop a global gravitational-wave network.

Project Management and Future Outlook

The timeline for CE includes phases of development, design, construction, and operation, drawing on the successful management strategies of LIGO. Estimated costs reach \$2061 million (2030 USD) for a two-observatory configuration, with detailed budgeting for civil engineering, vacuum systems, and detectors. Risk management strategies are outlined to address technological, environmental, and community-related risks.

In conclusion, Cosmic Explorer represents a substantial commitment to advancing our understanding of the universe through gravitational-wave science. The project outlines a plan to engage diverse communities, implement cutting-edge technology, and collaborate with international partners to achieve a transformative impact on astronomy, physics, and cosmology.