Below there is a list of the least massive known black holes, sorted by increasing mass. The unit of measurement is the solar mass, equivalent to kg.
List Name Mass() Distance(ly) Companion class Mass determination method Notes Refs.2MASS J05215658+4359220 10,000 Spectroscopic radial velocity measurements of noninteracting companion. In Milky Way outskirts. Recent Hubble ultraviolet data has suggested the companion to this object is actually a warm subgiant, and ruling out smaller compact companions such as a white dwarf. GW190425's remnant 518,600,000 Gravitational wave data of neutron star merger from LIGO and Virgo interferometers. 97% chance of prompt collapse into a black hole immediately after merger. Alternative study suggests collapse 2.5 hours later. NGC 3201-1 15,600 (see Notes) Spectroscopic radial velocity measurements of noninteracting companion. In globular cluster NGC 3201. Companion is 0.8 main sequence turn-off. GRO J1719-24/GRS 1716−249 8,500 Near-infrared photometry of companion and Eddington flux. LMXB system. 4U 1543-47 30,000 ± 3,500 Spectroscopic radial velocity measurements of companion. SXT system. XTE J1650-500 8,500 ± 2,300 Orbital resonance modeling from QPOs Transient binary X-ray source Determination of Black Hole Masses in Galactic Black Hole Binaries Using Scaling of Spectral and Variability Characteristics Shaposhnikov, Nickolai; Titarchuk, Lev; The Astrophysical Journal, Volume 699, Issue 1, pp. 453-468 (2009) PdfGRO J1655-40 <5,500 Precision X-ray timing observations from RossiXTE. LMXB system. GX 339-4 26,000
See also List of most massive black holes Stellar black hole List of lower mass gap objects
References