V4641 Sagittarii

V4641 Sagittarii

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]
Distance20,200 ± 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
Mass6.4±0.6 M☉
Stellar companion
Mass2.9±0.4 M☉
Radius5.3±0.3 R☉
Surface gravity (log g)3.5±0.1 cgs
Temperature10,250±300 K
Rotational velocity (v sin i)100.9±0.8 km/s
Other designations
V4641 Sgr, GSC 06848-03786, 2MASS J18192163-2524258[5]
Database references
SIMBADdata

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 1999 a violent X-ray outburst revealed it to contain a black hole.[6] 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,[7] 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.[7]

  1. ^ Cite error: The named reference Goranskij was invoked but never defined (see the help page).
  2. ^ a b c d e f Cite error: The named reference GaiaDR2 was invoked but never defined (see the help page).
  3. ^ a b "V4641 Sgr". International Variable Star Index. Retrieved 2021-03-17.
  4. ^ a b c d e Cite error: The named reference MacDonald_et_al_2014 was invoked but never defined (see the help page).
  5. ^ Cite error: The named reference SIMBAD was invoked but never defined (see the help page).
  6. ^ Cite error: The named reference NRAO_2000 was invoked but never defined (see the help page).
  7. ^ a b Cite error: The named reference Orosz_et_al_2001 was invoked but never defined (see the help page).