Realizing the promise of gravitational wave astronomy

Project Information

GWASTRO

Grant agreement ID: 896869

DOI

10.3030/896869

Project closed

EC signature date 20 April 2020

Start date 1 July 2021

End date 30 June 2023

Funded under

• EXCELLENT SCIENCE - Marie Skłodowska-Curie Actions

Total cost

€ 162 806,40

EU contribution

€ 162 806,40

Coordinated by

MAX-PLANCK-GESELLSCHAFT ZUR FORDERUNG DER WISSENSCHAFTEN EV
Germany

Periodic Reporting for period 1 - GWASTRO (Realizing the promise of gravitational wave astronomy)

Reporting period: 2021-07-01 to 2023-06-30

Summary of the context and overall objectives of the project

The detectors LIGO and Virgo hunt for gravitational waves from orbiting black holes and neutron stars; these compact objects lose energy through gravitational waves, spiral in towards each other and eventually merge. To analyze the data from the detections, it is crucial to have an accurate model of the expected gravitational waves. The merger process is highly dynamical and numerical simulations involving the Einstein equations are the only means to predict the gravitational waves from the merger. However, these simulations are too expensive for direct data analysis applications, each taking a month on a supercomputer. Therefore, fast but approximate waveform models that are calibrated against these simulations have been developed over the years, but these models do not currently capture all of the physics present in the simulations. Surrogate models take a data-driven approach to modeling, and are trained directly against numerical simulations without the need for additional assumptions. As a result, these models can rival the simulations themselves in accuracy. The main objective of this project is to develop novel surrogate models that capture the full physics of compact binary systems. Accurate models like this are necessary to maximize the output of our detectors for applications like black hole astrophysics, cosmology, understanding the neutron star equation of state, and fundamental tests of Einstein's general relativity.

Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far

During the two year period, this project led to 12 publications, in areas including numerical relativity, surrogate models, and black hole astrophysics.
Notable results include:
1. The first measurement of linear momentum of GWs. We use numerical relativity surrogate models to measure the recoil velocity of the final black hole left behind after a binary black hole merger. Because the binary radiates away linear momentum in preferred directions, the final black hole is imparted a recoil in the opposite direction. Measuring such a recoil has important implications like understanding how heavy stellar mass black holes form in nature, because if the recoils are large enough the final black hole would get ejected from its host galaxy rather than forming even heavier black holes through repeated mergers. This work resulted in the publication Physical Review Letters, 128, 191102 (2022), which was featured as an Editors Suggestion and received wide media coverage, for example, in news outlets like New Scientist, Discover Magazine, Science News, etc.
2. The first numerical simulations of black hole neutron star mergers in scalar tensor gravity. Such simulations are vital for providing predictions for the expected gravitational waves based on alternative theories of gravity. Given such predictions one can compare directly with observations to try and determine if alternative theories better fit the data than Einstein's general relativity. This work led to the publication Physical Review D, 107, 124051 (2023).

Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far)

The models developed as part of this project are expected to improve upon the previous best models by orders of magnitude in accuracy. Such improvements are necessary as we approach the high precision era of gravitational wave astronomy, with LIGO and Virgo expected to reach their design sensitivity soon, and with the 10x more sensitive next generation detectors planned for the 2030s. Unless our theoretical models continue to improve in order to keep up with these trailblazing experimental efforts, we cannot take full advantage of the detector improvements. The models developed in this project capture the full physics of numerical simulations, and can therefore help maximize the science output of current and upcoming detectors.

Kicked binary black hole