Gaia BH2
Gaia BH2 (Gaia DR3 5870569352746779008) is a binary system consisting of a red giant and what is very likely a stellar-mass black hole. Gaia BH2 is located about 3,800 light years away (1.16 kpc away) in the constellation of Centaurus, making it as of 2023 the second-closest known black hole system to Earth. Gaia BH2 is the second black hole discovered from Gaia DR3 astrometric data, and Gaia BH1 and BH2 are likely the only black hole binaries which will be detected from Gaia DR3 data.
| Observation data Epoch J2000 Equinox J2000 | |
|---|---|
| Constellation | Centaurus |
| Right ascension | 13h 50m 16.748s |
| Declination | −59° 14′ 20.33″ |
| Apparent magnitude (V) | 12.711 |
| Characteristics | |
| Red giant | |
| Evolutionary stage | Red giant |
| Black hole | |
| Evolutionary stage | Stellar black hole |
| Astrometry | |
| Radial velocity (Rv) | −5.04±2.08 km/s |
| Proper motion (μ) | RA: −10.48±0.1 mas/yr Dec.: −4.61±0.06 mas/yr |
| Parallax (π) | 0.859 ± 0.018 mas |
| Distance | 3,800 ± 80 ly (1,160 ± 20 pc) |
| Orbit | |
| Period (P) | 1,276.7±0.6 d |
| Semi-major axis (a) | 4.96±0.08 AU |
| Eccentricity (e) | 0.5176±0.0009 |
| Inclination (i) | 34.87±0.34° |
| Longitude of the node (Ω) | 266.9±0.5° |
| Periastron epoch (T) | 2457438.3±1.4 |
| Argument of periastron (ω) (secondary) | 130.9±0.4° |
| Semi-amplitude (K1) (primary) | 25.23±0.04 km/s |
| Details | |
| Red giant | |
| Mass | 1.07±0.19 M☉ |
| Radius | 7.77±0.25 R☉ |
| Luminosity (bolometric) | 24.6±1.6 L☉ |
| Surface gravity (log g) | 2.71±0.24 cgs |
| Temperature | 4,604±87 K |
| Metallicity [Fe/H] | −0.22±0.02 dex |
| Rotational velocity (v sin i) | <1.5 km/s |
| Black hole | |
| Mass | 8.94±0.34 M☉ |
| Other designations | |
| Database references | |
| SIMBAD | data |
The black hole and red giant orbit the system barycentre every 1,277 days, or around 3.5 years, with a moderate eccentricity of 0.518. The black hole's mass is around 8.94 M☉, which means its Schwarzschild radius should be about 26.4 km (16.4 mi). The red giant has a mass of 1.07 M☉ and a radius of 7.77 R☉. Its temperature is estimated at 4,604 K (4,331 °C; 7,828 °F).