GRO J0422+32

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GRO J0422+32[1] is an X-ray nova and black hole candidate that was discovered by the BATSE instrument on the CGRO satellite on 5 August 1992.[2][3] During outburst, it was observed to be stronger than the Crab Nebula gamma-ray source out to photon energies of about 500 keV.[4]

The mass of the black hole in GRO J0422+32 falls in the range 3.66 to 4.97 solar masses.[5] This is the smallest yet found for any black hole, and near the theoretical upper mass limit (~2.7 solar masses) for a neutron star. Further analysis in 2012 calculated a mass of 2.1 solar masses, which raises questions as to what the object actually is.[6]

Position (J2000) is RA 04 h 21 m 42.77 s +32 deg 54' 26.7".[7][8]

It is identified with an M1V variable star, V518 Per,[9] in the constellation Perseus, with magnitudes 13.5 in the B spectral band, and 13.2 in V.


  1. ^ [1] SIMBAD
  2. ^ Harmon, A. et al. (1992) IAUC 5584
  3. ^ Paciesas, W. et al. (1992), IAUC 5594
  4. ^ Ling, J. C. and Wm. A. Wheaton,"BATSE Soft γ-Ray Observations of GROJ0422+32", Ap. J., 584, 399 (2003)
  5. ^
  6. ^ Kreidberg, Laura; Bailyn, Charles D.; Farr, Will M.; Kalogera, Vicky (2012). "Mass Measurements of Black Holes in X-ray Transients: is There a Mass Gap?". The Astrophysical Journal 757 (36): 17pp. arXiv:1205.1805. Bibcode:2012ApJ...757...36K. doi:10.1088/0004-637x/757/1/36. 
  7. ^ McCroskey et al., IAUC 5594, 1992
  8. ^ Castro-Tirado, A. J. et al. (1993), Astron.&Astrophys, "Discovery of the optical counterpart of the soft X-ray transient GRO J0422+32", vol. 276, no2, pp. L37-L40
  9. ^ General Catalogue of Variable Stars, 3rd ed. (1971) Moscow