V723 Monocerotis

V723 Monocerotis is a variable star in the constellation Monoceros. It was proposed in 2021 to be a binary system including a lower mass gap black hole candidate nicknamed "The Unicorn".[1] Located 1,500 light years from Earth, it would be the closest black hole to our planet, and among the smallest ever found.[8][9]

V723 Monocerotis

A visual band light curve for V723 Monocerotis, adapted from Jayasinghe et al. (2021)[1]
Observation data
Epoch J2000.0      Equinox J2000.0
Constellation Monoceros
Right ascension 06h 29m 04.659s[2]
Declination −05° 34′ 20.23″[2]
Apparent magnitude (V) 8.21 - 8.42[3]
Characteristics
Spectral type G0II[4]
Variable type Ellipsoidal[5]
Astrometry
Proper motion (μ) RA: −1.347 mas/yr[2]
Dec.: 16.140 mas/yr[2]
Parallax (π)2.1748 ± 0.0331 mas[2]
Distance1,500 ± 20 ly
(460 ± 7 pc)
Absolute magnitude (MV)+0.93[6]
Orbit[1]
Period (P)59.9398 d
Eccentricity (e)0 (fixed)
Inclination (i)87.0+1.7
−1.4°
Argument of periastron (ω)
(secondary)		0 (fixed)°
Details
Giant star
Mass0.44±0.06[5] M☉
Radius22.5±1.0[5] R☉
Luminosity173±8[1] L☉
Surface gravity (log g)1.7±0.1[1] cgs
Temperature3,800±100[5] K
Metallicity [Fe/H]−0.9±0.1[1] dex
Rotational velocity (v sin i)15±2[5] km/s
Age5.4+5.1
−2.6[1] Gyr
Stripped subgiant
Mass2.8±0.3[5] M☉
Radius8.3±0.4[5] R☉
Temperature5,800±200[5] K
Rotational velocity (v sin i)70±10[5] km/s
Other designations
V723 Mon, BD−05 1649, HD 45762, HIP 30891, SAO 133321, PPM 189220[7]
Database references
SIMBADdata

Located in the Monoceros constellation, V723 Monocerotis is an eighth-magnitude ellipsoidal variable yellow giant star roughly the mass of the Sun, but 25 times its radius. The accompanying black hole was proposed to have a mass 3 times the mass of the Sun, corresponding to a Schwarzschild radius of 9 kilometers.[10][11]

Follow-up work in 2022 argued that V723 Monocerotis does not contain a black hole, but is a mass-transfer binary containing a red giant and a subgiant star that has been stripped of much of its mass.[5]

See also

References
  1. Jayasinghe, T.; et al. (2021-01-01). "A unicorn in monoceros: The 3 M⊙ dark companion to the bright, nearby red giant V723 Mon is a non-interacting, mass-gap black hole candidate". Monthly Notices of the Royal Astronomical Society. 504 (2): 2577–2602. arXiv:2101.02212. Bibcode:2021MNRAS.504.2577J. doi:10.1093/mnras/stab907.
  2. Brown, A. G. A.; et al. (Gaia collaboration) (2021). "Gaia Early Data Release 3: Summary of the contents and survey properties". Astronomy & Astrophysics. 649: A1. arXiv:2012.01533. Bibcode:2021A&A...649A...1G. doi:10.1051/0004-6361/202039657. S2CID 227254300. (Erratum: doi:10.1051/0004-6361/202039657e). Gaia EDR3 record for this source at VizieR.
  3. "V723 Mon". Variable Star Index. Retrieved 2022-03-23.
  4. Houk, N.; Swift, C. (1999), "Michigan catalogue of two-dimensional spectral types for the HD Stars", Michigan Spectral Survey, 5, Bibcode:1999MSS...C05....0H.
  5. El-Badry, Kareem; Seeburger, Rhys; Jayasinghe, Tharindu; Rix, Hans-Walter; Almada, Silvia; Conroy, Charlie; Price-Whelan, Adrian M.; Burdge, Kevin (2022). "Unicorns and giraffes in the binary zoo: Stripped giants with subgiant companions". Monthly Notices of the Royal Astronomical Society. 512 (4): 5620–5641. arXiv:2203.06348. Bibcode:2022MNRAS.512.5620E. doi:10.1093/mnras/stac815.
  6. Strassmeier, K.; Washuettl, A.; Granzer, Th.; Scheck, M.; Weber, M. (2000). "The Vienna-KPNO search for Doppler-imaging candidate stars. I. A catalog of stellar-activity indicators for 1058 late-type Hipparcos stars". Astronomy and Astrophysics Supplement Series. 142 (2): 275. Bibcode:2000A&AS..142..275S. doi:10.1051/aas:2000328.
  7. "V723 Mon". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2021-11-27.
  8. "Newfound black hole may be the closest to Earth". Science. 2021-04-29. Retrieved 2021-08-09.
  9. "A black hole dubbed 'the Unicorn' may be galaxy's smallest one". Reuters. 2021-04-22. Retrieved 2021-08-09.
  10. "Is the "Unicorn" the Closest Black Hole?". Sky & Telescope. 2021-04-23. Retrieved 2021-08-09.
  11. "Where is the nearest black hole to Earth?". BBC Sky at Night Magazine. Retrieved 2021-08-09.

Further reading
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