Exploring the Mass Segregation Effect of X-ray Sources in Globular Clusters. IV. Evidence of Black Hole Burning in $\omega$ Centauri

Abstract

Using X-ray sources as sensitive probes of stellar dynamical interactions in globular clusters (GCs), we study the mass segregation and binary burning processes in $\omega$ Cen. We show that the mass segregation of X-ray sources is quenched in $\omega$ Cen, while the X-ray source abundance of $\omega$ Cen is much smaller than other GCs, and the binary hardness ratio (defined as $L_{\mathrm{X}}/(L_{\mathrm{K}}{f}_b)$, with $f_b$ the binary fraction, $L_{\mathrm{X}}$ and $L_{\mathrm{K}}$ the cumulative X-ray and K band luminosity of GCs, respectively) of $\omega$ Cen is located far below the $L_{\mathrm{X}}/(L_{\mathrm{K}}{f}_b)-{\sigma }_c$ correlation line of the dynamically normal GCs. These evidences suggest that the binary burning processes are highly suppressed in $\omega$ Cen, and other "heating mechanisms", very likely a black hole subsystem (BHS), are essential in the dynamical evolution of $\omega$ Cen. Through the "black hole burning" processes (i.e., dynamical hardening of the BH binaries), the BHS is dominating the energy production of $\omega$ Cen, which also makes $\omega$ Cen a promising factory of gravitational-wave sources in the Galaxy.

13 pages, 3 figures, 1 table. Accepted for publication in ApJ