Narrow Results

The M87* black hole shadow observation by the Event Horizon Telescope (EHT) has enabled us to test the modified gravity theories in the extreme-field regime and estimating the black hole parameters. Having this assertion, we investigate the Kerr-like rotating black holes in 4D Einstein-Gauss-Bonnet (EGB) gravity and deduce their shadows. Considering the inclination angle θ₀ = 17^o, we show that the EGB black hole shadows are smaller and more distorted than for the Kerr black holes. Modelling the M87* black hole as the EGB black hole, we predict the shadow angular size 35.7888μas ≤ θ_d ≤ 39.6192μas. The M87* black hole shadow angular size θ_d = 42±3μas, within the 1σ region, constrains the GB coupling parameter and the black hole spin parameter. Interestingly, the circularity deviation of the EGB black hole shadows is smaller than the bounded deduced for the M87* black hole.

The shadow of a wall cast by the Sun on a soccer field has been used to measure the change of the altitude and azimuth of the Sun along the day and through the seasons. The change of curvature parameter of the daily hyperbola shadow’s path, has been recovered in the days around the spring equinox 2021. The study of the daily paths has been possible with chalk and meter during school days, on this field, and the data have been reported on a spreadsheet. The students were impressed by this whole-year experiment, while normally at school the experimental sessions are one-hour long.