VFTS 243 as predicted by the BPASS fiducial models

Understand

The recent discovery of an unambiguous quiescent BH and main sequence O star companion in VFTS 243 opens the door to new constraints on theoretical stellar evolution and population models looking to reproduce the progenitors of black hole - black hole binaries.

• Here we show that the Binary Population and Spectral Synthesis fiducial models (BPASSv2.2.1) natively predict VFTS243-like systems: We find that VFTS 243 likely originated from a binary system in a about 15 day orbit with primary mass ranging from 40 to 50 M$_{\odot}$ and secondary star with initial mass 24-25M$_{\odot}$.
• Additionally we find that the death of the primary star must have resulted in a low energy explosion E < 10$^{50}$ ergs.With a uniform prior we find that the kick velocity of the new-born black hole was <10 km/s.
• The very low eccentricity reported for VFTS 243 and the subsequent conclusion by the authors that the SN kick must have been very small is in line with the peak in the posterior distribution between 0 and 5 km/s found from our numerical simulations performed with a uniform prior.