The Formation of Rapidly Rotating Black Holes in High Mass X-ray Binaries

Understand

High mass X-ray binaries (HMXRBs) like Cygnus X-1, host some of the most rapidly spinning black holes (BHs) known to date, reaching spin parameters $a \gtrsim 0.84$.

• However, there are several effects that can severely limit the maximum BH spin parameter that could be obtained from direct collapse, such as tidal synchronization, magnetic core-envelope coupling and mass loss.
• Here we propose an alternative scenario where the BH is produced by a {\it failed} supernova (SN) explosion that is unable to unbind the stellar progenitor.
• A large amount of fallback material ensues, whose interaction with the secondary naturally increases its overall angular momentum content, and therefore, the spin of the BH when accreted.