Science with the Einstein Telescope: a comparison of different designs (2303.15923v2)

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 in each arm there is 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 simplemetrics' 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.

• The paper compares triangular and dual L-shaped designs for the Einstein Telescope, evaluating their sensitivity to compact binary coalescences, source localization, and parameter estimation.
• The study highlights how different configurations enhance capabilities for multi-messenger astronomy, particularly improving the detection and localization of kilonovae and gamma-ray bursts.
• Findings show varying performance across designs for detecting stochastic gravitational wave backgrounds and improving precision cosmology measurements with standard sirens.

Science with the Einstein Telescope: A Comparison of Different Designs

The paper on assessing the scientific potential of different design configurations for the Einstein Telescope (ET) provides a thorough examination of gravitational wave (GW) detection strategies and their implications for astrophysics, fundamental physics, and cosmology. This examination is centered around a comparative analysis of different geometrical arrangements and sensitivity configurations of the ET, a next-generation GW observatory funded through European efforts.

Overview of Research

The research focuses on a triangular configuration with three detectors, each with 10 km arms, compared with a dual L-shaped (2L) design comprising two detectors of varying arm lengths (either 15 km or 20 km). These geometrical configurations are evaluated for both a high-frequency (HF) instrument alone and a full-sensitivity configuration that combines HF instruments with a cryogenic low-frequency (LF) setup, collectively known as the xylophone model.

Key Findings

1. Sensitivity to Compact Binary Coalescences (CBCs): The triangular design demonstrates notable efficiency in CBC detection due to its unique geometry, which provides advantages in angular resolution capabilities at high frequencies. However, the 2L configurations with arms misaligned by 45 degrees demonstrate promising potential for improved source localization and parameter estimation, particularly in mid-to-low frequencies.
2. Implications for Multi-messenger Astronomy: The paper highlights the enhanced capabilities of ET configurations for multi-messenger astronomy, with the 2L configurations favorably impacting the detection of kilonovae and gamma-ray bursts in coordination with electromagnetic observatories. Pre-merger localization abilities are particularly emphasized, important for observing prompt gamma-ray bursts.
3. Stochastic Background Sensitivity: Assessing isotropic stochastic backgrounds, the triangular configuration is favored for high-frequency applications, while co-aligned 2L configurations excel around 10 Hz. The potential to detect cosmic string background and first-order phase transition peaks in the early Universe, therefore breaking new ground in investigating cosmological events, is apparent.
4. Physics of Black Holes and Neutron Stars (NSs): When evaluating the science drivers involving black hole spectroscopy and NS EOS constraints, the 2L configurations with 20 km arms improve the fidelity of tidal deformability measurements and nuclear physics implications. Such configurations could yield substantial increases in sensitivity to post-merger gravitational wave signals, revealing epochal information about NS mergers.
5. Precision Cosmology: For standard sirens capable of determining the Hubble constant and testing dark energy models, the 2L configurations display broadly superior performance due to better parameter estimation precision. This is crucial for high redshift studies and could potentially resolve existing tensions in cosmological measurements.
6. Dealing with Environmental Noise: The paper also explores the noise distractions from correlated sources such as magnetic fields and seismic activities, impacting both triangular and L-shaped designs differently, with L-shape configurations less susceptible to magnetic interference.

Conclusion

The comparative evaluation posits that while the triangular ET remains a solid performer, particularly due to its compact design minimizing environmental noise interference, trade-offs in sensitivity, localization prowess, and data synergy with electromagnetic instruments at different frequency bands suggest diversified applications across different configurations. For both scientific inquiry and practical implementation, the paper acknowledges that the choice between a triangle or L-shaped design pivots on specific science goals, affecting sources' detectability and descriptive data breadth.

Framed within an era marching towards third-generation gravitational wave detection, these findings offer pivotal guidance in decision-making processes regarding investments in future large-scale infrastructure for GW astronomy, solidifying the Europe's lead in a globally collaborative astrophysical endeavor.