HR 6819
| Observation data Epoch J2000.0 Equinox J2000.0 | |
|---|---|
| Constellation | Telescopium |
| Right ascension | 18h 17m 07.53179s[1] |
| Declination | −56° 01′ 24.0876″[1] |
| Apparent magnitude (V) | 5.36[2] (5.32 to 5.39[3]) |
| Characteristics | |
| Evolutionary stage | giant |
| Spectral type | B3IIIpe[4] or B3II/III[5] |
| B−V color index | −0.050±0.018[2] |
| Variable type | Be[6][3] |
| Astrometry | |
| Radial velocity (Rv) | +9.4±0.5[7] km/s |
| Proper motion (μ) | RA: -3.667[1] mas/yr Dec.: +11.120[1] mas/yr |
| Parallax (π) | 2.9148 ± 0.1828 mas[1] |
| Distance | 1,120 ± 70 ly (340 ± 20 pc) |
| Absolute magnitude (MV) | −1.47[2] |
| Orbit[7] | |
| Primary | QV Tel Aa |
| Companion | QV Tel Ab |
| Period (P) | 40.333±0.004 d |
| Eccentricity (e) | 0.03±0.01 |
| Argument of periastron (ω) (secondary) | 89° |
| Semi-amplitude (K1) (primary) | 61.3±0.6 km/s |
| Details[7] | |
| QV Tel Aa | |
| Mass | 6.3±0.7 M☉ |
| Radius | 5.5±0.5 R☉ |
| Surface gravity (log g) | 3.5-4.0 cgs |
| Temperature | 20,000±200 K |
| Rotational velocity (v sin i) | 50±1[8] km/s |
| QV Tel Ab (black hole) | |
| Mass | ≥ 5.0 ± 0.4 M☉ |
| QV Tel B | |
| Temperature | 14,125-19,953 K |
| Age | 15-75 Myr |
| Other designations | |
| Database references | |
| SIMBAD | data |
HR 6819, also known as HD 167128 or QV Telescopii (abbreviated QV Tel), is a triple star system in the southern constellation of Telescopium, in the south-western corner of the constellation, near its boundary with Pavo and Ara. The system appears as a variable star that is dimly visible to the naked eye with an apparent magnitude that ranges from 5.32 down to 5.39. It is 1,120 light years from the Sun, and is drifting farther away at a rate of 9.4 km/s. A May 2020 study reported it to contain a black hole, making the latter the closest known black hole, and the first one located in a stellar system visible to the naked eye. Because of its location in the sky, it is visible only to observers south of 33°N latitude.
Nomenclature
HR 6819 is the Bright Star Catalogue designation for this star. It also has a Henry Draper Catalogue designation HD 167128 and a Hipparcos designation HIP 89605.[9] Since its brightness varies, it has been given the variable star designation QV Telescopii, indicating that it is the 330th confirmed variable star (excluding stars with Bayer designations) in the constellation Telescopium.[6]
System
HR 6819 is a hierarchical triple containing a classical Be star in a wide orbit of unknown period around an inner 40.3 day binary, a B3 III star and a non-emitting (non-accreting) black hole (≥ 5±0.4 M☉), designated Ab.[7]
HR 6819 was regarded as a single star,[10] until astronomer Monika Maintz concluded the spectrum contained the signatures of two stars in 2009. However, extensive analysis was prevented by limited observations. This took place after more extensive radial velocity measurements by Thomas Rivinius and colleagues, suggesting the presence of an unseen stellar-mass black hole within the system.[7] Though the HR 6819 system has been described as a member of the Sco OB2 association of co-moving stars,[11] it has more recently been suggested to be an older system and not part of the association.[7]
The spectrum of HR 6819 contains both narrow and broadened lines. The broad lines originate from the rapidly-rotating Be star, while the narrow lines are from a more slowly-rotating B-class giant. The radial velocity variations of the lines indicate that the normal B giant is in a 40-day orbit, but not with the Be star. Therefore, there is a third, invisible, body in the system, the other component in the 40-day orbit. Analysis of the orbital parameters suggests that the third body is sufficiently massive that it can only be a black hole.[7]
QV Tel Aa
Designated Aa, the main, inner stellar component is a B3 III blue giant star. It has a mass of approximately 6 solar masses. It and the black hole form a binary with a period of 40.3 days.[7]
The spectral type of component Aa is well-defined at about B3 from the distinct narrow lines in the composite spectrum. Comparison of different spectral lines indicates that the star is a giant star with a temperature of 16 to 18 kK. The probable mass of such a star is 6.3 M☉, and certainly not less than 5 M☉.[7]
QV Tel Ab (black hole)
Radial velocity measurements of the inner component in 2020 suggested the presence of a massive unseen companion, which is hypothesized to be a black hole.[7] Being 1,120 light years distant from the Sun, this would make it the closest known black hole to the Sun and the first and only known black hole in a star system that is visible with the naked eye at apparent magnitude 5.36, making it one of the 2,000 brightest stellar systems.[2] The black hole is not detected in the spectrum and no x-rays have been observed, so it is assumed that it does not have an accretion disk.[7]
The orbital motion of the visible blue giant shows that the unseen component Ab has a minimum mass almost as large as component Aa. For the minimum mass 5 M☉ of component Aa, this means a minimum mass of 4.2 M☉. If the inclination of the orbit is not edge-on to us then the mass will be higher. Any star with a mass that high would be easily detected in the spectrum and objects which might be undetectable such as neutron stars cannot be that massive. Therefore, the object is assumed to be a black hole.[7]
QV Tel B
The second, outer stellar component designated as B is a type Be star with a stellar classification of B3IIIpe.[4] The 'e' suffix indicates emission lines in its spectrum. It is a rapidly rotating blue-white star with a hot disk of decreted gas surrounding it.[12] Samus et al. (2017) list this star as variable, although not properly of the Gamma Cassiopeiae type.[6] It is an estimated 50 million years in age,[13] with a projected rotational velocity of 50 km/s.[8]
The emission lines in the spectrum are strong, but absorption lines from the Be star are weak and so the exact spectral type is difficult to determine. Overall the spectral class is similar to the inner blue giant, but the relative weakness of some luminosity-dependant lines suggest that it is a main sequence star. It appears to be slightly hotter and slightly less luminous than the inner giant star, but the exact properties are difficult to determine due to its rapid rotation, the weak absorption lines, and the presence of strong emission lines from the disk.[7]
See also
References
- ^ a b c d e 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.
- ^ a b c d Anderson, E.; Francis, Ch. (2012). "XHIP: An extended Hipparcos compilation". Astronomy Letters. 38 (5): 331. arXiv:1108.4971. Bibcode:2012AstL...38..331A. doi:10.1134/S1063773712050015.
- ^ a b "QV Telescopii". Variable Star Index. Retrieved 6 May 2020.
- ^ a b Hiltner, W.A.; Garrison, R.F.; Schild, R.E. (July 1969). "MK spectral types for bright southern OB stars". The Astrophysical Journal. 157: 313. Bibcode:1969ApJ...157..313H. doi:10.1086/150069.
- ^ Houk, Nancy (1979). Michigan catalogue of two-dimensional spectral types for the HD stars. Vol. 1. Ann Arbor, Michigan: Department of Astronomy, University of Michigan. Bibcode:1978mcts.book.....H.
- ^ a b c Samus, N.N.; Kazarovets, E.V.; Durlevich, O.V.; Kireeva, N. N.; Pastukhova, E.N. (2017). "General Catalogue of Variable Stars". Astronomy Reports. 5.1. 61 (1): 80–88. Bibcode:2017ARep...61...80S. doi:10.1134/S1063772917010085.
- ^ a b c d e f g h i j k l m n Rivinius, Th.; Baade, D.; Hadrava, P.; Heida, M.; Klement, R. (2020). "A naked-eye triple system with a nonaccreting black hole in the inner binary". Astronomy & Astrophysics. 637 (L3): 11. arXiv:2005.02541. Bibcode:2020A&A...637L...3R. doi:10.1051/0004-6361/202038020.
- ^ a b Arcos, C.; Kanaan, S.; Chávez, J.; Vanzi, L.; Araya, I.; Curé, M. (March 2018). "Stellar parameters and H-α line profile variability of Be stars in the BeSOS survey". Monthly Notices of the Royal Astronomical Society. 474 (4): 5287–5299. arXiv:1711.08675. Bibcode:2018MNRAS.474.5287A. doi:10.1093/mnras/stx3075.
- ^ a b "HD 167128". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2020-02-14.
- ^ Eggleton, P.P.; Tokovinin, A.A. (September 2008). "A catalogue of multiplicity among bright stellar systems". Monthly Notices of the Royal Astronomical Society. 389 (2): 869–879. arXiv:0806.2878. Bibcode:2008MNRAS.389..869E. doi:10.1111/j.1365-2966.2008.13596.x.
- ^ Brown, A.G.A.; Verschueren, W. (1997). "High S/N Echelle spectroscopy in young stellar groups. II. Rotational velocities of early-type stars in SCO OB2". Astronomy and Astrophysics. 319: 811. arXiv:astro-ph/9608089. Bibcode:1997A&A...319..811B.
- ^ Jaschek, M.; Egret, D. (April 1982). "Catalog of Be stars". IAU Symposium. 98: 261. Bibcode:1982IAUS...98..261J.
- ^ Tetzlaff, N.; Neuhäuser, R.; Hohle, M.M. (January 2011). "A catalogue of young runaway Hipparcos stars within 3 kpc from the Sun". Monthly Notices of the Royal Astronomical Society. 410 (1): 190–200. arXiv:1007.4883. Bibcode:2011MNRAS.410..190T. doi:10.1111/j.1365-2966.2010.17434.x.
