ThorGW · Testing the horizon of black holes with gravitational waves
Horizon Europe — Marie Skłodowska-Curie Actions
- Duration
- 2024-05-01 → 2026-04-30
- EU contribution
- €173,847
- Participants
- 3
- Scheme
- HORIZON-TMA-MSCA-PF-EF
Lines connect the coordinator with its partners.
Results in brief
Testing the horizon of black holes with gravitational waves
Black holes are, in many ways, the simplest objects in the Universe. According to general relativity, black holes are described by only two parameters: their mass and their spin. Yet this apparent simplicity hides a profound mystery. A black hole is thought to be surrounded by an event horizon — a boundary beyond which nothing, not even light, can escape. At this surface, space and time effectively swap roles, and any information crossing it is forever hidden from the outside world. The black hole paradigm leads to deep puzzles. One of the most famous ones is the information-loss paradox, which questions whether information that falls into a black hole is truly lost forever. If so, this would clash with the fundamental laws of quantum physics, which state that information must be preserved. This raises a fascinating possibility: is the event horizon a physical surface, or is it a mathematical prediction of Einstein’s theory that might need revision? Gravitational waves offer a unique way to investigate this question. When two compact objects — such as black holes — orbit around each other, they gradually spiral inward and eventually merge. The newly formed object "rings" as it settles down, emitting gravitational waves like a bell produces sound. By measuring the frequency and how quickly these vibrations fade, we can infer the nature of the final object. If it has an event horizon, its ringing follows the predictions of general relativity. In the absence of a horizon, subtle differences may appear in the gravitational signal. The ThorGW project set out to explore exactly this possibility. First, it developed a general description of how compact objects without an event horizon would vibrate, and connected these predictions to observable gravitational-wave signals. Second, it used current data to place the first constraints on whether astrophysical black holes truly possess an event horizon. Finally, it looked ahead, forecasting how next-generation gravitational-wave detectors will sharpen these tests and bring us closer to answering one of the most fundamental questions about the nature of space and time.
Data: CORDIS, © European Union
Project objective
Gravitational waves (GWs) provide a unique opportunity to test gravity in a regime inaccessible to traditional astronomical observations. One of the main predictions of general relativity (GR) is the existence of black holes (BHs) featuring a horizon beyond which nothing — not even light — can escape. Observations of GWs from the remnants of binary BH coalescences have the potential to probe the physics at the horizon of BHs.This prospect is of particular interest given some quantum-gravity theories and dark matter models that predict the presence of horizonless compact objects, known as exotic compact objects (ECOs). ECOs emit a different GW signal than BHs due to the absence of a horizon. Studying their imprints in the postmerger stage allows one to investigate the existence of horizons in compact remnants.So far, the ground-based detectors LIGO and Virgo have detected GWs from the coalescence of binary BHs and neutron stars. Several tests on the properties of the remnants have been performed, setting constraints on generic deviations from general relativity. Current constraints can be converted into bounds on the location of the horizon by modelling the variations introduced by a generic class of ECOs. However, this aim has not been achieved given the open problems in modelling spinning ECOs, which I plan to tackle in this proposal.This project will provide the first bounds on the location of the horizon with current GW observations. For this purpose, I will extend the current state-of-the-art in ECO modelling to spinning configurations and develop new data-analysis schemes relating the postmerger GW signal to the horizon properties. Finally, I will assess the prospects of detectability of BH horizons with next-generation detectors, such as the ground-based Einstein Telescope and Cosmic Explorer and the space-based Laser Interferometer Space Antenna. The outcome of this project will provide novel tests of general relativity and shed light on quantum gravity.
Original text from CORDIS.
Participants
Links
- View on CORDIS
- DOI: 10.3030/101107586
- https://ec.europa.eu/research/participants/documents/downloadPublic?documentIds=080166e5140fc0fc&appId=PPGMS
- https://ec.europa.eu/research/participants/documents/downloadPublic?documentIds=080166e529be6097&appId=PPGMS
Data: CORDIS, © European Union