The mass of SS 433: a conflict resolved?

TL;DR

This paper resolves conflicting mass estimates of the SS 433 system by proposing that absorption lines originate from circumbinary disk material, indicating a system mass over 40 solar masses and suggesting a massive stellar black hole.

Contribution

It offers a reinterpretation of spectral absorption data, reconciling previous conflicting mass estimates and supporting the presence of a massive stellar black hole in SS 433.

Findings

Absorption spectra can be explained by circumbinary disk material absorption.

System mass of SS 433 exceeds 40 solar masses.

Supports the existence of a massive stellar black hole.

Abstract

The Galactic microquasar SS\,433 is very luminous and launches oppositely-directed jets of cool hydrogen at a quarter of the speed of light. Observations of emission lines from the circumbinary disk imply a system mass exceeding 40 $ M_\odot$. The most recent attempts to establish a mass via observation of absorption lines in the spectrum of the companion imply a system mass of no more than 20 $ M_\odot$. Aims. To examine these conflicting data and present a possible resolution of this conflict. Methods. Interpretation of data through the application of simple trigonometry to the configuration of the SS 433 system. Results. The absorption spectra which, attributed to the atmosphere of the companion, yield an orbital speed of $\sim$ 60 km s$^{-1}$ could well be attributable to absorption of light from the companion in material of the circumbinary disk. Then the absorption spectra predict an orbital speed for the circumbinary disk material of $\sim$ 240 km s$^{-1}$, in agreement with the emission line data. Conclusions. If continuum light from the companion is absorbed in passage through the circumbinary disk material rather than in the atmosphere of the companion itself, the periodic Doppler shifts in the absorption spectra are entirely consistent with observations of the circumbinary disk and a system mass exceeding $\sim$ 40 $M_\odot$. The striking consistency implies that the compact object is a rather massive stellar black hole.