Gaia BH2

Gaia BH2

DECaPS image of Gaia BH2 (star at the center)
Observation data Epoch J2000      Equinox J2000
Constellation	Centaurus
Right ascension	13^h 50^m 16.748^s[1]
Declination	−59° 14′ 20.33″[1]
Apparent magnitude (V)	12.711[2]
Characteristics
Red giant
Evolutionary stage	Red giant
Black hole
Evolutionary stage	Stellar black hole
Astrometry
Radial velocity (Rv)	−5.04±2.08[1] km/s
Proper motion (μ)	RA: −10.48±0.1 mas/yr[3] Dec.: −4.61±0.06 mas/yr[3]
Parallax (π)	0.859 ± 0.018 mas[3]
Distance	3,800 ± 80 ly (1,160 ± 20 pc)
Orbit[3]
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[3]
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
Gaia BH2, UCAC4 154-126202, 2MASS J13501675-5914203, Gaia DR3 5870569352746779008
Database references
SIMBAD	data

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 2024^[update] the third-closest known black hole system to Earth. Gaia BH2 is the second black hole discovered from Gaia DR3 astrometric data.[3]

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).[3]

Discovery

Gaia BH2 was originally discovered as a black hole binary candidate in 2022, found via astrometric observations with Gaia, along with Gaia BH1. At that time it was not clear if Gaia BH2 did definitely harbour a black hole, but it was the only plausible candidate in the Gaia data other than Gaia BH1.[4][5] Later radial velocity observations confirmed this black hole system and refined its orbital parameters.[3]

References

1. Vallenari, A.; et al. (Gaia collaboration) (2023). "Gaia Data Release 3. Summary of the content and survey properties". Astronomy and Astrophysics. 674: A1. arXiv:2208.00211. Bibcode:2023A&A...674A...1G. doi:10.1051/0004-6361/202243940. S2CID 244398875. Gaia DR3 record for this source at VizieR.
2. Zacharias, N.; Finch, C. T.; Girard, T. M.; Henden, A.; Bartlett, J. L.; Monet, D. G.; Zacharias, M. I. (2012-07-01). "VizieR Online Data Catalog: UCAC4 Catalogue (Zacharias+, 2012)". VizieR Online Data Catalog: I/322A. Bibcode:2012yCat.1322....0Z.
3. El-Badry, Kareem; Rix, Hans-Walter; Cendes, Yvette; Rodriguez, Antonio C.; Conroy, Charlie; Quataert, Eliot; Hawkins, Keith; Zari, Eleonora; Hobson, Melissa; Breivik, Katelyn; Rau, Arne; Berger, Edo; Shahaf, Sahar; Seeburger, Rhys; Burdge, Kevin B. (2023-02-01). "A red giant orbiting a black hole". Monthly Notices of the Royal Astronomical Society. 521 (3): 4323–4348. arXiv:2302.07880. Bibcode:2023MNRAS.521.4323E. doi:10.1093/mnras/stad799.
4. El-Badry, Kareem; Rix, Hans-Walter; Quataert, Eliot; Howard, Andrew W.; Isaacson, Howard; Fuller, Jim; Hawkins, Keith; Breivik, Katelyn; Wong, Kaze W. K.; Rodriguez, Antonio C.; Conroy, Charlie; Shahaf, Sahar; Mazeh, Tsevi; Arenou, Frédéric; Burdge, Kevin B. (2023-01-01). "A Sun-like star orbiting a black hole". Monthly Notices of the Royal Astronomical Society. 518 (1): 1057–1085. arXiv:2209.06833. Bibcode:2023MNRAS.518.1057E. doi:10.1093/mnras/stac3140. ISSN 0035-8711.
5. Tanikawa, Ataru; Hattori, Kohei; et al. (September 2022). "Search for a Black Hole Binary in Gaia DR3 Astrometric Binary Stars with Spectroscopic Data". The Astrophysical Journal. 946 (2): 79. arXiv:2209.05632. Bibcode:2023ApJ...946...79T. doi:10.3847/1538-4357/acbf36.