A new heavyweight champion for stellar mass BHsquestionMark XMM and Chandra investigate

The Xray source associated with the M31 globular cluster Bovirgul135 (hereafter XBo135) may contain the largest stellar mass black hole (BH) to date. It has beenobserved several times with Chandra and XMMNewton, and has always exhibitedemission spectra characteristic of the BH low state. XBo 135 exhibited thisbehaviour at virgul46E+38 erg/s, suggesting a primary mass >50 Solar masses.Possible formation scenarios include stellar mergers in the cluster center, orthe direct collapse of a metal poor high mass star. We request 120 ks ofXMMNewton time to investigate the metalicity, and a 5 ks Chandra pointing toaccurately locate the source. These observations will test the feasibility ofthese scenarios; in particular, a high metalicity will rule out direct collapse. truncated!, Please see actual data for full text [truncated!, Please see actual data for full text]