In May 2023, the Cosmic Explorer Project requested Science Letters to support our community response to ngGW, the NSF Directorate for Mathematical & Physical Sciences Next-Generation Gravitational Wave Observatory Subcommittee. The ngGW Subcommittee had been asked to recommend GW detection network configurations that will deliver a detector with sensitivity an order of magnitude greater than the LIGO A+ design. The Cosmic Explorer community response included the following Letters:

• C. Fryer, GW Compact Remnant Mass Constraints as Probes of the Supernova Engine, CE-P2300002
• L. van Son et al., What we need from XG observatories to unveil the birth, life and death of massive stars – Part 1: births, CE-P2300014
• F. Broekgaarden et al., What we need from XG observatories to unveil the birth, life and death of massive stars – Part 2: life, CE-P2300015
• L. van Son et al., What we need from XG observatories to unveil the birth, life and death of massive stars – Part 3: stellar death, CE-P2300016
• I. Bartos et al., Orbital Eccentricity as the Fingerprint of Merger Origin, CE-P2300010
• T. Mishra et al., Probing black hole growth with Intermediate mass black holes, CE-P2300011
• P. Landry et al., Next-generation dense matter science with binary neutron star inspirals, CE-P2300013,
• E. R. Most and C. A. Raithel, Resolving Phase Transitions in the Neutron Star Equation924 of State, CE-P2300006
• A. Haber, M. G. Alford and E. R. Most, How Third Generation Gravitational Wave Detectors Can Unveil the True Degrees of Freedom of Dense Matter, CE-P2300004
• C. A. Raithel and V. Paschalidis, New Probes of the Finite-Temperature Dense-Matter Equation of State with Cosmic Explorer, CE-P2300012
• R. Sambruna, F. Civano and B. Humensky, Synergies of future ground-based GW detectors with space assets for multi messenger Astrophysics, CE-L2300011
• E. Murphy et al., Synergies between Cosmic Explorer and the ngVLA, CE-P2300009
• S. Gossan and E. D. Hall, Optimizing XG detector networks for Galactic astrophysics, CE-P2300017
• O. Gottlieb, Detecting Gravitational-waves from Collapsar Cocoons with the Cosmic Explorer, CE-P2300003
• M. Ball and R. Frey, Galactic Magnetars and Cosmic Explorer, CE-P2300010
• A. Grant et al., Gravitational-Wave Memory Effects in XG Observatories, CE-L2300012
• H. -J. Kuan et al., Gravitational phase transitions with Cosmic Explorer, CE-P2300007
• R. Essick and M. Isi, Distinguishing scalar gravitational-wave polarizations with next-generation detectors, CE-P2300008
• S.-J. Jin, Forecast for cosmological parameters in the era of the third-generation gravitational-wave detectors, CE-P2300005

These Letters, and their exploration of the science potential of Cosmic Explorer, were an esential contribution to the development of the Cosmic Explorer White Paper to be submitted to ngGW for the June 12 deadline.

Call for Science Letters

The NSF Directorate for Mathematical & Physical Sciences has asked the Next-Generation Gravitational Wave Observatory Subcommittee (ngGW) to recommend GW detection network configurations that will deliver a detector with sensitivity an order of magnitude greater than the LIGO A+ design. The Cosmic Explorer Project is requesting Science Letters to support our community response to ngGW.

Science Letters are informal public documents that will explore the scientific potential of next-generation (XG) gravitational-wave observatory networks. Each Science Letter should outline the capabilities and timelines needed for an XG network to address a specific science question. Science Letters are encouraged to suggest benchmarks that will ensure that the XG network is capable of the breakthrough science that they describe.

An XG network may include a combination of Cosmic Explorer, Einstein Telescope, Nemo, and upgraded detectors in current and planned ~4km-scale facilities (LIGO-US, LIGO-India, Virgo, KAGRA). Science Letters should focus on desired observational capabilities rather than specific sites or configurations.

Each Science Letter should contain a maximum of 2 pages of text and figures, as well as authors and relevant references. They should use clear and straightforward language that is understandable for scientists from a variety of fields. Contact information (names and email address) for corresponding Authors should be included in the Science Letter. Information for additional endorsing Authors may also be included.

Our ngGW White Papers (pdf) will draw from benchmarks in the Science Letters for network comparisons and science traceability. Cosmic Explorer White Paper teams may be recruited based on Science Letter authorship. Science Letters do not preclude independent White Paper authorship.

We encourage all members of the Cosmic Explorer Consortium to collaborate on Science Letters and to engage early career researchers and graduate students in the process. Science Letters that include authors with diverse backgrounds, perspectives, and experiences are essential. Authors do not need to be Consortium members. You may list letters in progress and points of contact in this spreadsheet to encourage collaboration and coordination.

Science Letters should be uploaded to the Cosmic Explorer DCC and added to the Science Letters Event or submitted using this CE Science Letter Form. Letters are requested by May 8 to best enable their use in White Papers.

Thank you in advance for your contributions! We look forward to reading your Science Letters, and to working together to advance our understanding of the Universe through gravitational-wave observations.

FAQ

Is there a recommended format?

We have a suggested Overleaf Template that we encourage you to use.

What are benchmarks?

A benchmark should represent a desired observational capability, such as detection rate or sensitivity, that can be used to differentiate between potential XG networks. Science Letters should explain how reaching certain benchmarks would ensure that gravitational-wave astronomy contributes to new knowledge pathways.

Example benchmarks could include:

• Characteristic strain sensitivity between 10 and 100 Hz.
• Number of sources with 10 deg² localization available 5 minutes before merger.
• Number of BBH mergers detected per year with SNR > 600.
• Horizon distance for BNS observations relative to peak star formation redshift.
• Number of BBH and BNS detected at redshift larger than 2.
• Integrated 1-year sensitivity to stochastic backgrounds with a fractional energy density Ω_GW(f) in gravitational waves .
• Sensitive range for a burst that releases E_GW of 10^-9 M_⊙c² at 1 kHz.
• Ellipticity of known pulsars with measurable quadrupole emission.
• Sensitive range for a long-duration source of some characteristic timescale and h_RSS.

The potential scale of XG network capabilities can be seen in studies including [2109.09882] A Horizon Study for Cosmic Explorer: Science, Observatories, and Community and [2303.15923] Science with the Einstein Telescope: a comparison of different designs.

What detector network or locations should I use?

Because the exact configuration of the ngGW network is in active development, we ask that Science Letters focus on desired observational requirements instead of specific detector locations and configurations. White Paper teams may later reach out to Science Letter authors to collaborate on assessing the science capabilities of candidate networks.

What topics might science letters address?

• Key science questions addressed by gravitational-wave observations of mergers, unmodeled transients, long-duration or continuous signals, and stochastic backgrounds.
• Multi-messenger astronomy potential with gravitational waves, including joint observations with other telescopes and detectors.
• Potential contributions of XG observatories to open questions in areas including cosmology, high energy physics, particle physics, and nuclear physics.
• Interdisciplinary impacts of XG development, such as applications in materials science, data science, or quantum optics.
• Neglected or overlooked areas of XG science with high potential impact.

Where can I ask additional questions?

Please reach out to Jocelyn Read (jread AT fullerton.edu) and Salvatore Vitale (svitale AT mit.edu) with any questions about the Science Letters.