Common envelope ejection in massive binary stars - Implications for the progenitors of GW150914 and GW151226

Understand

The recently detected gravitational wave signals (GW150914 and GW151226) of the merger event of a pair of relatively massive stellar-mass black holes (BHs) calls for an investigation of the formation of such progenitor systems in general.

• We analyse the common envelope (CE) stage of the "traditional" formation channel in binaries where the first-formed compact object undergoes an in-spiral inside the envelope of its evolved companion star and ejects the envelope in that process.
• We calculate envelope binding energies of donor stars with initial masses between 4 and 115 Msun for metallicities of Z=Zsun/2 and Z=Zsun/50, and derive minimum masses of in-spiralling objects needed to eject these envelopes.
• We find that CE evolution, besides from producing WD-WD and NS-NS binaries, may, in principle, also produce massive BH-BH systems with individual BH component masses up to ~50-60 Msun, in particular for donor stars evolved to giants.