Letter | Published:

Is Cyg X-1 a neutron star?

Naturevolume 247pages351352 (1974) | Download Citation



WE suggest that the source of X-ray emission Cygnus X-1 may be a neutron star in orbit about an early-type relatively unevolved star, both of which are in orbit about the massive 09.7Iab (ref 13) supergiant star DH226868. From an analysis of HD226868, Bolton1 derives the following parameters for the system: M1 20M, M2 11M, A 3 × 1012cm, i 30°, P ≈ 5.6 d, L 1039erg s−1 and T 30,000 K, where M1 and M2 are the masses of the primary and secondary components respectively, A is the separation of the centres of the components, i is the inclination, P the orbital period, L the luminosity and T the effective temperature. It has been suggested by numerous authors (for example refs 1–3) that the source of the X radiation is the unseen secondary, which, since it is massive and since it must be compact to produce X rays, is likely to be a black hole.

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  1. Institute of Astronomy, Madingley Road, Cambridge, CB3 OHA

    • A. C. FABIAN
    • , J. E. PRINGLE
    •  & J. A. J. WHELAN


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