The evolution of runaway stellar collision products

Abstract

In the cores of young dense star clusters, repeated stellar collisions involving the same object can occur. It has been suggested that this leads to the formation of an intermediate-mass black hole. To verify this scenario we compute the detailed evolution of the merger remnant of three sequences, then follow the evolution until the onset of carbon burning, and estimate the final remnant mass to determine the ultimate fate of a runaway merger sequence. We use a detailed stellar evolution code to follow the evolution of the collision product. At each collision we mix the two colliding stars, accounting for the mass loss during the collision. During the stellar evolution we apply mass-loss rates from the literature, as appropriate for the evolutionary stage of the merger remnant. We computed models for high (Z = 0.02) and low (Z = 0.001) metallicity to quantify metallicity effects. We find that the merger remnant becomes a Wolf-Rayet star before the end of core hydrogen burning. Mass loss from stellar winds dominates the mass increase due to repeated mergers for all three merger sequences that we consider. In none of our high-metallicity models an intermediate-mass black hole is formed, instead our models have a mass of 10-14 M at the onset of carbon burning. For low metallicity the final remnant is more massive and may explode as a pair-creation supernova. We find that our metal-rich models become inflated as a result of developing an extended low-density envelope. This may increase the probability of further collisions, but self-consistent N-body calculations with detailed evolution of runaway mergers are required to verify this.

Search for gravitational waves from intermediate mass binary black holes

“…Another model [26] studies the progressive accumulation of mass into a large (> 50 M ) seed black hole via coalescence of a population of smaller black holes. However, the existence of binaries with IMBH components remains uncertain since stellar winds may stall the growth of the IMBH progenitors in the runaway collision scenario [27], or the merger recoil may also eject a newly formed black hole from the globular cluster [28,29].…”

Radiation Hydrodynamical Models for Type I Superluminous Supernovae

“…In close binary systems, a merger (or even multiple mergers) of the C+O core from an evolved WR star with another hydrogen-deficient star, like a neutron star, a white dwarf, or WR star could occur [6,10,18]. Such processes could form a dense C+O CSM or common envelope.…”

Massive binaries and the enrichment of the interstellar medium in globular clusters

“…Various authors have inferred highly nonconservative evolution for Algols, systems which are currently undergoing stable mass transfer (e.g., Refsdal et al 1974;de Greve & Linnell 1994;Figueiredo et al 1994;van Rensbergen et al 2006;† Glebbeek et al (2009) suggested that a chain of multiple stellar collisions in the dense centre of a star cluster may also enrich the interstellar medium with processed material. et al 2007).…”