Stellar wind retention and expulsion in massive star clusters

Abstract

Mass and energy injection throughout the lifetime of a star cluster contributes to the gas reservoir available for subsequent episodes of star formation and the feedback energy budget responsible for ejecting material from the cluster. In addition, mass processed in stellar interiors and ejected as winds has the potential to augment the abundance ratios of currently forming stars, or stars which form at a later time from a retained gas reservoir. Here we present hydrodynamical simulations that explore a wide range of cluster masses, compactnesses, metallicities and stellar population age combinations in order to determine the range of parameter space conducive to stellar wind retention or wind powered gas expulsion in star clusters. We discuss the effects of the stellar wind prescription on retention and expulsion effectiveness, using MESA stellar evolutionary models as a test bed for exploring how the amounts of wind retention/expulsion depend upon the amount of mixing between the winds from stars of different masses and ages. We conclude by summarizing some implications for gas retention and expulsion in a variety of compact (σ v 20 kms −1 ) star clusters including young massive star clusters (10 5 M/M 10 7 , age 500 Myrs), intermediate age clusters (10 5 M/M 10 7 , age ≈ 1 − 4 Gyrs), and globular clusters (10 5 M/M 10 7 , age 10 Gyrs).

The Close Stellar Companions to Intermediate-Mass Black Holes

“…The lower series of lines uses the wind velocity and orbital properties to estimate the fraction captured by the IMBH. The shaded region denotes the range of possible Bondi accretion rates onto a 150 M e IMBH with ambient gas density of 10 −24 g cm −3 and sound speed c s =10 6 -10 7 cm s −1 (Naiman et al , 2013, where M bondi =4π (G M bh ) 2 ρ/c s 3 . Stellar winds are only captured by the IMBH less than 10% of the time.…”

Disruption of the Orion molecular core 1 by wind from the massive star θ1 Orionis C

“…Mechanical and radiative energy input by massive stars stir up the environment, heat the gas, produce cloud & intercloud phases in the interstellar medium and disrupt molecular clouds, the birthsites of new stars1,2. Ionization by UV photons, stellar wind action and supernova explosions control molecular clouds lifetimes3,4,5,6,7. Theoretical studies predict that momentum injection by radiation dominates by far over momentum injected by a stellar wind8, but this has hitherto been difficult to assess observationally.…”

Modelling gas evacuation mechanisms in present-day globular clusters: stellar winds from evolved stars and pulsar heating

“…All models result in electron and hydrogen densities that are consistent with observational constraints. This is due to the combination of the lower metallicity and smaller mass of M15 in comparison to 47 Tuclower metallicity results in higher overall stellar winds (Figure 2) and the smaller mass of M15 produces a gravitational potential which is slightly less conducive to retaining large central density reservoirs (Naiman et al 2018).…”

“…Within the cluster, emanating winds from the dense stellar population and millisecond pulsars, when present, are assumed to shock and thermalize and, as such, the mass and energy contributions are implemented as source terms in the hydrodynamical equations. In spherical symmetry, the hydrodynamical equations may be written following the simplified forms presented in Naiman et al (2018) as:…”

“…Because we are employing spherically symmetric simulations, these rates must encompass the average mass-loss properties of the stellar population as a whole. Following Naiman et al (2018), we derive the average mass-loss rate and wind velocity for a population of stars from the logic presented in Kroupa et al (2013). The average mass ∆M(t i ) and kinetic energy ∆E K (t i ) injection within the cluster at a time t i by a population of stars of M [M L , M H ] born as a single stellar population at time t 0 may then be formalized (Naiman et al 2018):…”