BASS DR2 Sample Excludes Thermal Photospheres Expected from Horizonless Compact Objects in Local AGNs

The analysis drew on the Swift BAT AGN Spectroscopic Survey DR2, selecting a clean subsample of z < 0.1 AGNs with high-quality optical and X-ray spectra. Researchers searched for the broad thermal continuum expected from an accretion-powered photosphere that forms rapidly around any horizonless object. None of the spectra showed this feature, directly contradicting predictions that hold across naked-singularity, gravastar, and other mimicker scenarios independent of microphysical details.

This result extends the horizon-scale imaging tests performed on M87* and Sgr A* to a statistical population, converting single-object constraints into population-level evidence. Prior work on individual sources left room for model-dependent loopholes; the absence of photospheric emission across dozens of AGNs closes those loopholes for the sampled objects while remaining consistent with standard thin-disk emission around Kerr black holes.

Future X-ray and infrared spectroscopy with XRISM and JWST can raise sensitivity enough to test the remaining sources, potentially requiring horizons in more than 80 percent of the BASS sample within three years. The key limitation remains incomplete wavelength coverage for fainter objects; deeper, simultaneous multi-band observations would eliminate residual model space.