Open AccessStellar encounters involving massive stars in young clusters
Author(s) -
Davies Melvyn B.,
Bate Matthew R.,
Bonnell Ian A.,
Bailey Ver C.,
Tout Christopher A.
Publication year - 2006
Publication title -
monthly notices of the royal astronomical society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.058
H-Index - 383
eISSN - 1365-2966
pISSN - 0035-8711
DOI - 10.1111/j.1365-2966.2006.10644.x
Subject(s) - physics , astrophysics , stars , star cluster , blue straggler , astronomy , binary star , radius , mass segregation , star (game theory) , star formation , binary number , cluster (spacecraft) , stellar dynamics , stellar mass , stellar collision , stellar mass loss , stellar density , stellar evolution , computer security , arithmetic , mathematics , computer science , programming language
We model collisions between pre‐main‐sequence stars using a smoothed particle hydrodynamics method. Assuming that all collisions lead to simple mergers, we use derived merger cross‐sections to calculate the time‐scale to make a 50‐M ⊙ star by collisions within the core of a stellar cluster as a function of stellar number density. We show that a 50‐M ⊙ star may be produced in this manner within 10 6 yr beginning with a cluster core of 200 1‐M ⊙ stars within a radius of 0.0025 pc. Encounters between one high‐mass star and one low‐mass star tend to result in the tidal shredding of the latter, producing a massive disc around the former. This disc spreads viscously and provided a much larger target than any star for subsequent collisions. If a star strikes the disc, it is likely to be captured, and so forms a binary with the other star. Subsequent encounters between the binary and single stars lead either to exchanges or to the formation of merged objects. The inclusion of this effect leads to a significant reduction in the time taken to produce a 50‐M ⊙ star. We also consider the role played by primordial binaries. We show that the time‐scale required to produce a 50‐M ⊙ star decreases with increasing binary fraction. We find that the number of primordial binaries is reduced by encounters. The core of a cluster must therefore contain a very high binary fraction initially if a large fraction of the massive stars are to be contained within binaries when the 50‐M ⊙ star is produced.