On the possible connection between galactic featureless-spectrum sources and stellar-mass black holes

The problem of direct detection of a black hole event horizon still remains unresolved. Isolated stellar-mass black holes could be ideal objects for solving this problem, since the event horizon would not be screened by the surrounding interstellar plasma due to its low accretion rate. We search for black hole candidates in their presumed birth locations, computed in the assumption that they could have originated in high-mass binaries. Theories predict that isolated black holes should exhibit featureless flat spectra covering the entire electromagnetic range. Objects classified as DC dwarfs (cool white dwarfs with featureless continuum spectra) are among such galactic sources, and they also constitute a good sample for searching for possible black hole candidates among them. We analyze sources with available spectral, photometric, and proper motion data. The final list contains 5 sources that fit the selection criteria.