Unique microquasar SS433: new results, new issues

TL;DR

This paper presents 45 years of observational data on the microquasar SS433, revealing its evolutionary orbital period increase, stable Roche lobe size, and other key system parameters, advancing understanding of its unique relativistic jets and binary dynamics.

Contribution

It provides new long-term observational insights into SS433, including orbital period increase, system stability, and jet behavior, highlighting the system's evolutionary state and black hole nature.

Findings

Orbital period increasing at 1.14e-7 s/s

Distance between components increasing over time

Stable Roche lobe size and orbital parameters

Abstract

The unique microquasar SS433 is a massive X-ray binary system at an advanced evolutionary stage. The optical star overflows its Roche lobe and transfers mass at a very high rate onto a black hole surrounded by a supercritical accretion disk with relativistic jets inclined to the orbital plane. Both disk and jets precess with a period of 162.3 days. In the outer parts of the precessing jets, emission lines of hydrogen and neutral helium are formed, moving periodically across the spectrum of SS433 with an enormous amplitude of $\sim 1000$\,\AA\ or, on the $\sim 50000$ km/s velocity scale. A 30-year spectral and photometric monitoring of SS433 has been carried out at Sternberg Astronomical Institute. Using all published data for 45 years of observations, we obtained a number of important results concerning the nature of this unique microquasar. We discovered a secular evolutionary increase in the orbital period of SS433 at a rate of $(1.14 \pm 0.25)\times 10^{-7}$ seconds per second, suggesting that the relativistic object in SS433 is a black hole with mass exceeding 8\,${\rm M}_\odot$. It is shown that the distance between the components of SS433 increases with time, which prevents the formation of a common envelope in the system. The size of the Roche lobe of the optical donor star is on average constant in time, which ensures a stable secondary mass exchange in the system. The orbital ellipticity of SS433 was discovered, strongly supporting the model of a slaved accretion disk tracking the precession of the rotation axis of the optical star, which is inclined to the orbital plane due to an asymmetric supernova explosion. Parameters of the kinematic model of SS433, except for the precession period, keep on average constant for 45 years. Phase jumps of the precession period were detected, but on average the precession period remains constant for 45 years. (Abridged)