Gaia BH2
Observation data
Epoch J2000      Equinox J2000
Constellation Centaurus
Right ascension 13h 50m 16.748s[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]
Distance3,800 ± 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
Mass1.07±0.19 M☉
Radius7.77±0.25 R☉
Luminosity (bolometric)24.6±1.6 L☉
Surface gravity (log g)2.71±0.24 cgs
Temperature4,604±87 K
Metallicity [Fe/H]−0.22±0.02 dex
Rotational velocity (v sin i)<1.5 km/s
Black hole
Mass8.94±0.34 M☉
Other designations
Gaia BH2, UCAC4 154-126202, 2MASS J13501675-5914203, Gaia DR3 5870569352746779008
Database references
SIMBADdata

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.[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. ^ a b c 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. ^ a b c d e f g 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.
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