V4641 Sagittarii

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V4641 Sagittarii
V4641SgrLightCurve.png
A visual band light curve for V4641 Sagittarii, adapted from Goranskij (2001) [1]
Observation data
Epoch J2000.0        Equinox J2000.0
Constellation Sagittarius
Right ascension 18h 19m 21.63427s [2]
Declination −25° 24′ 25.8493″ [2]
Apparent magnitude  (V)9.0 - 14.0 [3]
Characteristics
Spectral type B9III [4]
Variable type HMXB/BHXB/XN+ELL+E [3]
Astrometry
Proper motion (μ)RA: −0.734 [2] mas/yr
Dec.: +0.418 [2] mas/yr
Parallax (π)0.1510±0.0413  mas [2]
Distance 20,200 ± 2,300 [4]   ly
Orbit [4]
Period (P)2.81730 d
Semi-major axis (a)17.5±1.0  R☉
Inclination (i)72.3±4.1°
Periastron epoch (T)2,452,423.647
Semi-amplitude (K2)
(secondary)		211.3±1.0 km/s
Details [4]
Black hole
Mass 6.4±0.6  M☉
Stellar companion
Mass 2.9±0.4  M☉
Radius 5.3±0.3  R☉
Surface gravity (log g)3.5±0.1  cgs
Temperature 10,250±300  K
Rotational velocity (v sin i)100.9±0.8 km/s
Other designations
V4641 Sgr, AAVSO 1813-25B, GSC 06848-03786, 2MASS J18192163-2524258 [5]
Database references
SIMBAD data

V4641 Sagittarii is a variable X-ray binary star system in the constellation Sagittarius. It is the source of one of the fastest superluminal jets in the Milky Way galaxy.

In 1978, Vitaly Petrovich Goranskij announced the detection of an outburst from this star. It was erroneously identified as a previously known mira variable, GM Sagittarii. Several additional outbursts of the star over the next few years were also attributed to GM Sagittarii. In 1999, it was noticed that the flaring star was about 72 arcseconds north of GM Sagittarii, and the flaring star was given its own variable star designation, V4641 Sagittarii. [6] [7] [8]

In 1999 a violent X-ray outburst revealed it to contain a black hole. [9] At the time, it was considered to be the closest known black hole to Earth, at a distance of approximately 1,600 light-years (490  pc ). Later observations showed it to be much farther away, reported in 2001 to be between 7.4 and 12.31  kpc , [10] 6.2 kpc in 2014, [4] and around 6.6 kpc according to its Gaia Data Release 2 parallax. [2]

The star in the binary system is a late B class giant with a mass about three times that of the Sun. It orbits a black hole about twice as massive every 2.8 days. The star is distorted, which causes variations in its brightness as it orbits and rotates. It is also slightly eclipsed by an accretion disc around the black hole. The system usually does not produce a significant amount of x-rays, but undergoes outbursts when the x-ray luminosity increases due to accretion onto the black hole driving superluminal jets. [10]

V4641 Sgr is a source of ultra-high-energy gamma rays. [11]

References

  1. ↑ Goranskij, V. P. (May 2001). "The Orbital V-band Light Curve of V4641 Sagittarii". Information Bulletin on Variable Stars. 5068: 1. Bibcode:2001IBVS.5068....1G . Retrieved 13 March 2022.
  2. 1 2 3 4 5 6 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.
  3. 1 2 "V4641 Sgr". International Variable Star Index. Retrieved 2021-03-17.
  4. 1 2 3 4 5 MacDonald, Rachel K. D.; et al. (March 2014). "The Black Hole Binary V4641 Sagitarii: Activity in Quiescence and Improved Mass Determinations". The Astrophysical Journal. 784 (1): 19. arXiv: 1401.4190 . Bibcode:2014ApJ...784....2M. doi:10.1088/0004-637X/784/1/2. S2CID   119279780. 2.
  5. ↑ "V4641 Sgr". SIMBAD . Centre de données astronomiques de Strasbourg . Retrieved 2021-03-16.
  6. ↑ Goranskij, V. P. (1978). "Variable stars in Sagittarius". Astronomicheskii Tsirkulyar. 1024: 3–4. Bibcode:1978ATsir1024....3G.
  7. ↑ Goranskij, V. P. (May 1990). "GM Sagittarii: Strange Light Changes in a Binary System". Information Bulletin on Variable Stars. 3464: 1–4. Bibcode:1990IBVS.3464....1G . Retrieved 23 September 2025.
  8. ↑ Samus, N. N.; Hazen, M.; Williams, D.; Welther, B.; Williams, G. V.; Hoffleit, D. (October 1999). "V4641 Sagittarii and GM Sagittarii". IAU Circular. 7277. Bibcode:1999IAUC.7277....1S . Retrieved 23 September 2025.
  9. ↑ "Dramatic Outburst Reveals Nearest Black Hole". National Radio Astronomy Observatory . January 14, 2000. Retrieved 2008-08-30.
  10. 1 2 Orosz, J. A.; et al. (July 2001). "A Black Hole in the Superluminal Source SAX J1819.3-2525 (V4641 SGR)". The Astrophysical Journal. 555 (1): 489–503. arXiv: astro-ph/0103045 . Bibcode:2001ApJ...555..489O. doi:10.1086/321442. S2CID   50248739. Finally, we find a distance in the range 7.40 ≤ d ≤ 12.31 kpc (90% confidence), which is at least a factor of ≈ 15 larger than the initially assumed distance of ≈ 1,600 light-years/500 pc.
  11. ↑ Alfaro, R.; Alvarez, C.; Arteaga-Velázquez, J. C.; Avila Rojas, D.; Ayala Solares, H. A.; Babu, R.; Belmont-Moreno, E.; Caballero-Mora, K. S.; Capistrán, T.; Carramiñana, A.; Casanova, S.; Cotti, U.; Cotzomi, J.; Coutiño de León, S.; De la Fuente, E.; Depaoli, D.; Di Lalla, N.; Diaz Hernandez, R.; Dingus, B. L.; DuVernois, M. A.; Durocher, M.; Díaz-Vélez, J. C.; Engel, K.; Espinoza, C.; Fan, K. L.; Fang, K.; Fraija, N.; Fraija, S.; García-González, J. A.; Garfias, F.; Gonzalez Muñoz, A.; González, M. M.; Goodman, J. A.; Groetsch, S.; Harding, J. P.; Herzog, I.; Hinton, J.; Huang, D.; Hueyotl-Zahuantitla, F.; Hüntemeyer, P.; Iriarte, A.; Joshi, V.; Kaufmann, S.; Kieda, D.; de León, C.; Lee, J.; León Vargas, H.; Linnemann, J. T.; Longinotti, A. L.; Luis-Raya, G.; Malone, K.; Martinez, O.; Martínez-Castro, J.; Matthews, J. A.; Miranda-Romagnoli, P.; Morales-Soto, J. A.; Moreno, E.; Mostafá, M.; Nayerhoda, A.; Nellen, L.; Newbold, M.; Nisa, M. U.; Noriega-Papaqui, R.; Olivera-Nieto, L.; Omodei, N.; Osorio, M.; Pérez Araujo, Y.; Pérez-Pérez, E. G.; Rho, C. D.; Rosa-González, D.; Ruiz-Velasco, E.; Salazar, H.; Salazar-Gallegos, D.; Sandoval, A.; Schneider, M.; Serna-Franco, J.; Smith, A. J.; Son, Y.; Springer, R. W.; Tibolla, O.; Tollefson, K.; Torres, I.; Torres-Escobedo, R.; Turner, R.; Ureña-Mena, F.; Varela, E.; Villaseñor, L.; Wang, X.; Watson, I. J.; Willox, E.; Yun-Cárcamo, S.; Zhou, H. (17 October 2024). "Ultra-high-energy gamma-ray bubble around microquasar V4641 Sgr". Nature. 634 (8034): 557–560. arXiv: 2410.16117 . doi:10.1038/s41586-024-07995-9. PMID   39415065.
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