Stellar-mass black holes in the SDSS

Models suggest a synchrotron spectrum in visible wavelengths and some emission in X-ray wavelengths. Of 3.7 million objects in the Sloan Digital Sky Survey Early Data Release, Cat. <J/AJ/123/567>, about 150,000 objects have colors and properties consistent with such a spectrum, and 87 of these objects are X-ray sources from the ROSAT All-Sky Survey (Cat. <IX/10> and <IX/29>).

Thirty-two of these have been confirmed not to be black holes using optical spectra. We give the positions and colors of these 55 black hole candidates and quantitatively rank them on their likelihood to be black holes. We discuss uncertainties in the expected number of sources and the contribution of black holes to local dark matter.