Revisiting the dynamical case for a massive black hole in IC10 X-1

Silas G.T. Laycock, Thomas J. Maccarone, Dimitris M. Christodoulou

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36 Scopus citations


The relative phasing of the X-ray eclipse ephemeris and optical radial velocity (RV) curve for the X-ray binary IC10 X-1 suggests that the He [λ4686] emission line originates in a shadowed sector of the stellar wind that avoids ionization by X-rays from the compact object. The line attains maximum blueshift when the wind is directly towards us at mid X-ray eclipse, as is also seen in Cygnus X-3. If the RV curve is unrelated to stellar motion, evidence for a massive black hole (BH) evaporates because the mass function of the binary is unknown. The reported X-ray luminosity, spectrum, slow QPO and broad eclipses caused by absorption/scattering in the Wolf-Rayet (WR) wind are all consistent with either a low-stellar-mass BH or a neutron star (NS). For an NS, the centre of mass lies inside the WR envelope whose motion is then far below the observed 370 km s-1 RV amplitude, while the velocity of the compact object is as high as 600 km s-1. The resulting 0.4 per cent Doppler variation of X-ray spectral lines could be confirmed by missions in development. These arguments also apply to other putative BH binaries whose RV and eclipse curves are not yet phase-connected. Theories of BH formation and predicted rates of gravitational wave sources may need revision.

Original languageEnglish
Pages (from-to)L31-L35
JournalMonthly Notices of the Royal Astronomical Society: Letters
Issue number1
StatePublished - Jun 26 2015


  • Accretion, accretion discs
  • Black hole physics
  • Circumstellar matter
  • Stars: Neutron
  • X-rays: Binaries


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