V723 Monocerotis

V723 Monocerotis is a variable star in the constellation Monoceros. It is proposed to be a binary system including a lower mass gap black hole candidate nicknamed "The Unicorn".[4] Located 1,500 light years from Earth, it may be the closest black hole to our planet, and the smallest one ever found.[6][7]

V723 Monocerotis
Observation data
Epoch J2000.0      Equinox J2000.0
Constellation Cetus
Right ascension 06h 29m 04.659s[1]
Declination −05° 34′ 20.23″[1]
Apparent magnitude (V) 8.3[2]
Characteristics
Spectral type G0II[3]
Astrometry
Proper motion (μ) RA: −1.513[1] mas/yr
Dec.: 15.840[1] mas/yr
Parallax (π)2.175 ± 0.033[4] mas
Distance1,500 ± 20 ly
(460 ± 7 pc)
Orbit[4]
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[4]
Giant star
Mass1.00±0.07 M☉
Radius24.9±0.7 R☉
Luminosity173±8 L☉
Surface gravity (log g)1.7±0.1 cgs
Temperature4,570±60 K
Metallicity [Fe/H]−0.9±0.1 dex
Rotational velocity (v sin i)19.1±1 km/s
Age5.4+5.1
−2.6 Gyr
Dark companion
Mass3.04±0.06 M☉
Radius3×10−6 R☉
Other designations
V723 Mon, BD−05 1649, HD 45762, HIP 30891, SAO 133321, PPM 189220[5]
Database references
SIMBADdata

Located in the Monoceros constellation, V723 Monocerotis is an eighth-magnitude ellipsoidal variable red giant star roughly the mass of the Sun, but 25 times its diameter. Its accompanying black hole is believed to have a mass 2.6 times the mass of the Sun, corresponding to a Schwarzschild radius of about 10 kilometers.[8][9]

See also

References
  1. Brown, A. G. A.; et al. (Gaia collaboration) (August 2018). "Gaia Data Release 2: Summary of the contents and survey properties". Astronomy & Astrophysics. 616. A1. arXiv:1804.09365. Bibcode:2018A&A...616A...1G. doi:10.1051/0004-6361/201833051. Gaia DR2 record for this source at VizieR.
  2. Høg, E.; Fabricius, C.; Makarov, V. V.; Urban, S.; Corbin, T.; Wycoff, G.; Bastian, U.; Schwekendiek, P.; Wicenec, A. (2000). "The Tycho-2 catalogue of the 2.5 million brightest stars". Astronomy and Astrophysics. 355. Bibcode:2000A&A...355L..27H.
  3. Houk, N.; Swift, C. (1999), "Michigan catalogue of two-dimensional spectral types for the HD Stars", Michigan Spectral Survey, 5, Bibcode:1999MSS...C05....0H.
  4. 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. doi:10.1093/mnras/stab907.
  5. "V723 Mon". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2021-11-27.
  6. "Newfound black hole may be the closest to Earth". Science. 2021-04-29. Retrieved 2021-08-09.
  7. "A black hole dubbed 'the Unicorn' may be galaxy's smallest one". Reuters. 2021-04-22. Retrieved 2021-08-09.
  8. "Is the "Unicorn" the Closest Black Hole?". Sky & Telescope. 2021-04-23. Retrieved 2021-08-09.
  9. "Where is the nearest black hole to Earth?". BBC Sky at Night Magazine. Retrieved 2021-08-09.

Further reading
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