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Concurrent formation of supermassive stars and globular clusters : Implications for early self-enrichment

Gieles, Mark ; Charbonnel, Corinne ; Krause, Martin G.H. ; Hénault-Brunet, Vincent ; Agertz, Oscar LU ; Lamers, Henny J.G.L.M. ; Bastian, Nathan ; Gualandris, Alessia ; Zocchi, Alice and Petts, James A. (2018) In Monthly Notices of the Royal Astronomical Society 478(2). p.2461-2479
Abstract

We present a model for the concurrent formation of globular clusters (GCs) and supermassive stars (SMSs, ≳103M) to address the origin of the HeCNONaMgAl abundance anomalies in GCs. GCs form in converging gas flows and accumulate low-angular momentum gas, which accretes on to protostars. This leads to an adiabatic contraction of the cluster and an increase of the stellar collision rate. A SMS can form via runaway collisions if the cluster reaches sufficiently high density before two-body relaxation halts the contraction. This condition is met if the number of stars ≳106 and the gas accretion rate ≳105M Myr-1, reminiscent of GC formation in high gas-density environments,... (More)

We present a model for the concurrent formation of globular clusters (GCs) and supermassive stars (SMSs, ≳103M) to address the origin of the HeCNONaMgAl abundance anomalies in GCs. GCs form in converging gas flows and accumulate low-angular momentum gas, which accretes on to protostars. This leads to an adiabatic contraction of the cluster and an increase of the stellar collision rate. A SMS can form via runaway collisions if the cluster reaches sufficiently high density before two-body relaxation halts the contraction. This condition is met if the number of stars ≳106 and the gas accretion rate ≳105M Myr-1, reminiscent of GC formation in high gas-density environments, such as - but not restricted to - the early Universe. The strong SMS wind mixes with the inflowing pristine gas, such that the protostars accrete diluted hot-hydrogen burning yields of the SMS. Because of continuous rejuvenation, the amount of processed material liberated by the SMS can be an order of magnitude higher than its maximum mass. This 'conveyor-belt' production of hot-hydrogen burning products provides a solution to the mass budget problem that plagues other scenarios. Additionally, the liberated material is mildly enriched in helium and relatively rich in other hot-hydrogen burning products, in agreement with abundances of GCs today. Finally, we find a super-linear scaling between the amount of processed material and cluster mass, providing an explanation for the observed increase of the fraction of processed material with GC mass. We discuss open questions of this new GC enrichment scenario and propose observational tests.

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author
organization
publishing date
type
Contribution to journal
publication status
published
subject
keywords
Galaxies: star clusters: general, Globular clusters: general, Stars: abundances, Stars: black holes, Stars: kinematics and dynamics, Supergiants
in
Monthly Notices of the Royal Astronomical Society
volume
478
issue
2
pages
19 pages
publisher
Oxford University Press
external identifiers
  • scopus:85051524550
ISSN
0035-8711
DOI
10.1093/MNRAS/STY1059
language
English
LU publication?
yes
id
b2ccd751-92af-4591-aee7-fa28d25087ce
date added to LUP
2019-02-07 11:08:10
date last changed
2020-03-24 06:39:06
@article{b2ccd751-92af-4591-aee7-fa28d25087ce,
  abstract     = {<p>We present a model for the concurrent formation of globular clusters (GCs) and supermassive stars (SMSs, ≳10<sup>3</sup>M<sub>⊙</sub>) to address the origin of the HeCNONaMgAl abundance anomalies in GCs. GCs form in converging gas flows and accumulate low-angular momentum gas, which accretes on to protostars. This leads to an adiabatic contraction of the cluster and an increase of the stellar collision rate. A SMS can form via runaway collisions if the cluster reaches sufficiently high density before two-body relaxation halts the contraction. This condition is met if the number of stars ≳10<sup>6</sup> and the gas accretion rate ≳10<sup>5</sup>M<sub>⊙</sub> Myr<sup>-1</sup>, reminiscent of GC formation in high gas-density environments, such as - but not restricted to - the early Universe. The strong SMS wind mixes with the inflowing pristine gas, such that the protostars accrete diluted hot-hydrogen burning yields of the SMS. Because of continuous rejuvenation, the amount of processed material liberated by the SMS can be an order of magnitude higher than its maximum mass. This 'conveyor-belt' production of hot-hydrogen burning products provides a solution to the mass budget problem that plagues other scenarios. Additionally, the liberated material is mildly enriched in helium and relatively rich in other hot-hydrogen burning products, in agreement with abundances of GCs today. Finally, we find a super-linear scaling between the amount of processed material and cluster mass, providing an explanation for the observed increase of the fraction of processed material with GC mass. We discuss open questions of this new GC enrichment scenario and propose observational tests.</p>},
  author       = {Gieles, Mark and Charbonnel, Corinne and Krause, Martin G.H. and Hénault-Brunet, Vincent and Agertz, Oscar and Lamers, Henny J.G.L.M. and Bastian, Nathan and Gualandris, Alessia and Zocchi, Alice and Petts, James A.},
  issn         = {0035-8711},
  language     = {eng},
  month        = {08},
  number       = {2},
  pages        = {2461--2479},
  publisher    = {Oxford University Press},
  series       = {Monthly Notices of the Royal Astronomical Society},
  title        = {Concurrent formation of supermassive stars and globular clusters : Implications for early self-enrichment},
  url          = {http://dx.doi.org/10.1093/MNRAS/STY1059},
  doi          = {10.1093/MNRAS/STY1059},
  volume       = {478},
  year         = {2018},
}