47 Tucanae X9

47 Tucanae X9

Artistic representation of 47 Tucanae X9
Observation data
Epoch J2000.0      Equinox ICRS
Constellation Tucana[1]
Right ascension 00h 24m 04.26s[2]
Declination −72° 04′ 58.0″[2]
Apparent magnitude (V) 19.772[3]
Characteristics
Evolutionary stage Black hole + white dwarf[4]
Spectral type WD
Orbit
Period (P)28.18 minutes
Other designations
47 Tuc X9, RX J0021.8-7221, CXOGlb J002404.2-720458[2]
Database references
SIMBADdata

47 Tucanae X9 (also known as 47 Tuc X9) is an ultracompact low-mass X-ray binary (LMXB) located within the globular cluster 47 Tucanae, one of the brightest and most massive globular cluster in the Milky Way Galaxy, situated approximately 14,800 light-years away in the constellation of Tucana.[5] The system is notable for being the first confirmed black hole-white dwarf binary in the Milky Way, with an exceptionally short orbital period of approximately 28.18 minutes.[6]

Discovery and observations

47 Tuc X9 was discovered using NASA Chandra X-ray Observatory, NuSTAR and the Australia Telescope Compact Array (ATCA).[7][8] Initially the system was classified as a cataclysmic variable with a white dwarf primary,[9] subsequent radio and X-ray observations reclassified it as an LMXB with a black hole. An alternative hypothesis of a neutron star (possibly a transitional millisecond pulsar) was considered but deemed less likely due to the absence of pulsations and the system's ultracompact orbit.[10]

Formation and evolution

The ultracompact orbit of 47 Tuc X9 likely resulted from dynamical interactions in the dense environment of 47 Tucanae, such as a black hole capturing a white dwarf or evolving from a black hole/helium-star binary through mass transfer and gravitational wave emission. The high stellar density of the globular cluster facilitates the formation of such compact binaries.[6]

References

  1. ↑ Roman, Nancy G. (1987). "Identification of a constellation from a position". Publications of the Astronomical Society of the Pacific. 99 (617): 695. Bibcode:1987PASP...99..695R. doi:10.1086/132034. Constellation record for this object at VizieR.
  2. 1 2 3 "RX J0021.8-7221". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2025-10-01.
  3. ↑ Albrow, Michael D.; Gilliland, Ronald L.; Brown, Timothy M.; Edmonds, Peter D.; Guhathakurta, Puragra; Sarajedini, Ata (2001). "The Frequency of Binary Stars in the Core of 47 Tucanae". The Astrophysical Journal. 559 (2): 1060. arXiv:astro-ph/0105441. Bibcode:2001ApJ...559.1060A. doi:10.1086/322353.
  4. ↑ "Chandra :: Photo Album :: X9 in 47 Tucanae :: More Images of X9 in 47 Tucanae". chandra.harvard.edu. Retrieved 2025-09-17.
  5. ↑ "Star Discovered in Closest Known Orbit Around Likely Black Hole - NASA". 2017-03-13. Retrieved 2025-09-18.
  6. 1 2 Bahramian, Arash; Heinke, Craig O.; Tudor, Vlad; Miller-Jones, James C. A.; Bogdanov, Slavko; Maccarone, Thomas J.; Knigge, Christian; Sivakoff, Gregory R.; Chomiuk, Laura (2017-02-07). "The ultracompact nature of the black hole candidate X-ray binary 47 Tuc X9". Monthly Notices of the Royal Astronomical Society. 467 (2): 2199–2216. arXiv:1702.02167. Bibcode:2017MNRAS.467.2199B. doi:10.1093/mnras/stx166.
  7. ↑ "Chandra :: Photo Album :: 47 Tucanae :: March 13, 2017". chandra.harvard.edu. Retrieved 2026-07-07.
  8. ↑ Byrd, Deborah (2017-03-15). "Closest-yet star to black hole | Space | EarthSky". Retrieved 2025-09-17.
  9. ↑ Paresce, Francesco; De Marchi, Guido; Ferraro, Francesco R. (November 1992). "Possible cataclysmic variable in the core of the globular cluster 47 Tucanae". Nature. 360 (6399): 46–48. Bibcode:1992Natur.360...46P. doi:10.1038/360046a0. ISSN 1476-4687.
  10. ↑ News Staff (2017-03-14). "Astronomers Find Record-Breaking White-Dwarf-Black-Hole Binary in Globular Cluster 47 Tucanae | Astronomy | Sci-News.com". Sci.News: Breaking Science News. Retrieved 2025-09-17.
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