Scientific Objectives of Einstein Telescope

TL;DR

The paper advocates for a third-generation gravitational-wave detector, Einstein Telescope (ET), with a sensitivity window of $1$ Hz to $10$ kHz and substantially better strain sensitivity to enable a broad science program beyond current advanced detectors. It analyzes ET's triangular topology, the ability to form a null data stream and resolve polarizations, and the anticipated data-analysis challenges, including mock data challenges. The authors outline five key scientific objectives—cosmology, fundamental physics, cosmography, nuclear physics, and astrophysics—demonstrating ET's potential to probe black hole seed formation, test general relativity in strong fields, measure cosmological parameters via standard sirens, constrain neutron star equations of state, and observe supernovae in real time. They provide concrete examples, such as IMBH observations at high redshift, QNM-based tests of gravity, and standard siren-based cosmography, to illustrate ET's transformative impact on multiple disciplines. Overall, ET is presented as essential for accessing a richer, deeper gravitational-wave universe and for enabling precision tests across cosmology, nuclear physics, and high-energy astrophysics.

Abstract

The advanced interferometer network will herald a new era in observational astronomy. There is a very strong science case to go beyond the advanced detector network and build detectors that operate in a frequency range from 1 Hz-10 kHz, with sensitivity a factor ten better in amplitude. Such detectors will be able to probe a range of topics in nuclear physics, astronomy, cosmology and fundamental physics, providing insights into many unsolved problems in these areas.

Figures (4)

• Figure 1: The plot shows the cumulative number of compact binary events expected to be detected by a network within a given distance, for three archetypal compact binaries and four different advanced detector networks. The curves flatten (and stay constant) upon reaching the horizon distance of the network, the distance beyond which a network cannot detect signals with the desired signal-to-noise ratios. See the text for further details.
• Figure 2: Triangular topology of ET, in which each arm of length $L$ is used twice to form three detectors with a 60-degree opening angle, is equivalent to that of two L-shaped detectors of length $3L/4,$ whose arms house two detectors in each Freise:2008dk. (Arms are drawn to scale.)
• Figure 3: Antenna pattern of the Virgo interferometer (top) compared to that of ET (bottom) located at the same site.
• Figure 4: The top panel shows ET's strain sensitivity for two optical configurations, ET-B ET-B and ET-D Hild:2010id. The bottom panel plots ET-B's distance reach for compact binary mergers as a function of the observed total mass (blue dashed curves) and intrinsic total mass (red solid curves) for non-spinning binaries (lower curves) and binaries with dimensionless spins of $0.75$ (upper curves).