Science with the Einstein Telescope: a comparison of different designs

Abstract

The Einstein Telescope (ET), the European project for a third-generation gravitational-wave detector, has a reference configuration based on a triangular shape consisting of three nested detectors with 10 km arms, where each detector has a 'xylophone' configuration made of an interferometer tuned toward high frequencies, and an interferometer tuned toward low frequencies and working at cryogenic temperature. Here, we examine the scientific perspectives under possible variations of this reference design. We perform a detailed evaluation of the science case for a single triangular geometry observatory, and we compare it with the results obtained for a network of two L-shaped detectors (either parallel or misaligned) located in Europe, considering different choices of arm-length for both the triangle and the 2L geometries. We also study how the science output changes in the absence of the low-frequency instrument, both for the triangle and the 2L configurations. We examine a broad class of simple 'metrics' that quantify the science output, related to compact binary coalescences, multi-messenger astronomy and stochastic backgrounds, and we then examine the impact of different detector designs on a more specific set of scientific objectives.

Rapid Premerger Localization of Binary Neutron Stars in Third-generation Gravitational-wave Detectors

“…We choose 10 different negative latencies (from 50 minutes to postmerger) and the curves show the cumulative distribution of 90% areas of events that are detected at those times. data down to ∼3 Hz and trigger even earlier detections (Borhanian & Sathyaprakash 2022;Branchesi et al 2023). However, BNS with high negative latencies are not likely to be well localized until more data comes in, bringing higher S/Ns, wider frequency bands, and a longer equivalent network baseline.…”

“…Several third-generation (3G) GW detectors have been proposed, including Einstein Telescope (ET; Punturo et al 2010) and Cosmic Explorer (CE; Reitze et al 2019;Evans et al 2023), with low-frequency sensitivities significantly improved. These would allow us to detect BNS signals more than 30 minutes before the merger, rendering precise early-warning localization possible (Chan et al 2018;Akcay 2019;Nitz & Dal Canton 2021;Borhanian & Sathyaprakash 2022;Ronchini et al 2022;Branchesi et al 2023).…”

“…We will build a fast localization algorithm based on the above multibanding scheme. Given the large number of BNS detections in the 3G detectors (typically ∼10 5 per year; Borhanian & Sathyaprakash 2022;Branchesi et al 2023), an efficient and light algorithm is necessary. While machine-learning methods (Dax et al 2021;Gabbard et al 2022) are gradually making progresses, Bayestar (Singer & Price 2016), which performs a five-fold numerical marginalization over nuisance extrinsic parameters, has been used as the standard low-latency localization approach throughout the observing runs of the current generation of GW detectors.…”

Kinematic anisotropies and pulsar timing arrays

“…These findings -of which many are new while others are known but we set them in a new perspective -can be useful to plan future PTA observations. In fact, as we can plan the location of ground based interferometers in the Earth in order to extract most physics from observations (for example, see the recent study [66] in the context of the Einstein Telescope), we can also plan which pulsars are worth monitoring to learn new physics from GW measurements. This is an invaluable opportunity for forthcoming observations with SKA facilities, which will monitor and detect signals from a large number of pulsars [67] with important opportunities for GW physics: see e.g.…”

What Can We Learn about the Unstable Equation-of-state Branch from Neutron Star Mergers?

“…In recent years, astrophysical measurements of NS properties from X-ray (Miller & others NICER collaboration 2019;Riley & others NICER collaboration 2019;Miller & others NICER collaboration 2021;Riley & others NICER collaboration 2021), radio (Demorest et al 2010;Antoniadis et al 2013;Cromartie et al 2019;Fonseca et al 2021), and gravitational-wave (GW) observations of the inspiral phase of binary neutron star (BNS) mergers (Abbott et al 2017(Abbott et al , 2018(Abbott et al , 2019(Abbott et al , 2020 have provided a wealth of information on the EOS (see, e.g., Bauswein et al 2017;Margalit & Metzger 2017;Annala et al 2018;Most et al 2018;Ruiz et al 2018;Landry & Essick 2019;Radice & Dai 2019;Capano et al 2020;Dietrich et al 2020;Essick et al 2020;Raaijmakers et al 2020Raaijmakers et al , 2021Ghosh et al 2022;Huth et al 2022;Pang et al 2022). While these observations already led to exciting results, the era of high-precision astrophysical measurements of the EOS is yet to come, with the next generation of GW detectors being planned in the United States (Reitze et al 2019;Evans & others Cosmic Explorer Consortium 2021) and Europe (Punturo et al 2010;Branchesi et al 2023), and improved large-area X-ray timing telescopes anticipated in the future (e.g., Gaskin et al 2019;Mushotzky et al 2019;Zhang et al 2019).…”