How to tell an accreting boson star from a black hole
Hector Olivares, Ziri Younsi, Christian M. Fromm, Mariafelicia De, Laurentis, Oliver Porth, Yosuke Mizuno, Heino Falcke, Michael Kramer and, Luciano Rezzolla

TL;DR
This paper demonstrates that the Event Horizon Telescope can distinguish boson stars from black holes by their different observational signatures at 230 GHz, due to the absence of an event horizon and matter accumulation effects.
Contribution
The study provides the first detailed simulated images of non-rotating boson stars at horizon scales, showing observable differences from black holes using EHT data.
Findings
Boson stars exhibit matter accumulation in their interior unlike black holes.
Differences in images are due to the absence of an event horizon and related dynamical effects.
EHT can potentially identify horizonless objects through these observational signatures.
Abstract
The capability of the Event Horizon Telescope (EHT) to image the nearest supermassive black hole candidates at horizon-scale resolutions offers a novel means to study gravity in its strongest regimes and to test different models for these objects. Here, we study the observational appearance at 230 GHz of a surfaceless black hole mimicker, namely a non-rotating boson star, in a scenario consistent with the properties of the accretion flow onto Sgr A*. To this end, we perform general relativistic magnetohydrodynamic simulations followed by general relativistic radiative transfer calculations in the boson star space-time. Synthetic reconstructed images considering realistic astronomical observing conditions show that, despite qualitative similarities, the differences in the appearance of a black hole -- either rotating or not -- and a boson star of the type considered here are large enough…
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