Testing the Kerr-Scalarmaron Metric with Time-Domain Filtering of Sgr A*'s Shadow

While Paul et al. (2024) introduced the Kerr-scalaron metric and used static shadow observations to constrain it, and Shiokawa et al. (2017) developed time-domain filtering for Sgr A* simulations, no one has combined these approaches. This research would apply time-domain filtering to actual EHT observations of Sgr A* to search for temporal signatures specific to the Kerr-scalaron metric. The hypothesis is that the scalaron field would create unique temporal patterns in the shadow variability - perhaps different frequency-dependent brightness distributions or phase relationships compared to Kerr predictions. By filtering the data at different temporal frequencies and comparing the resulting "time-sliced" shadows against both Kerr and Kerr-scalaron GRMHD simulations, we could potentially detect subtle deviations from general relativity that are completely invisible in static images. This represents a fundamentally new way to test alternative gravity theories using the temporal dimension of black hole observations.

References:

1. Kerr-scalaron Metric and Astronomical Consequences near the Galactic Center Black Hole. Debojit Paul, Pranjali Bhattacharjee, S. Kalita (2024). Astrophysical Journal.
2. Time Domain Filtering of Resolved Images of Sgr A∗. H. Shiokawa, C. Gammie, S. Doeleman (2017).