Do the majority of stars form as gravitationally unbound?

Abstract

Some of the youngest stars (age $\lesssim 10$ Myr) are clustered, while many others are observed scattered throughout star forming regions or in complete isolation. It has been intensively debated whether the scattered or isolated stars originate in star clusters, or if they form truly isolated, which could help constrain the possibilities how massive stars are formed. We adopt the assumption that all stars form in gravitationally bound star clusters embedded in molecular cloud cores ($\Gamma$-$1$ model), which expel their natal gas, and compare the fraction of stars found in clusters with observational data. The star clusters are modelled by the code nbody6, which includes stellar and circumbinary evolution, gas expulsion, and the external gravitational field of their host galaxy. We find that small changes in the assumptions in the current theoretical model estimating the fraction, $\Gamma$, of stars forming in embedded clusters have a large influence on the results, and we present a counterexample as an illustration. This calls into question theoretical arguments about $\Gamma$ in embedded clusters, and it suggests that there is no firm theoretical ground for low $\Gamma$ in galaxies with lower star formation rates (SFRs). Instead, the assumption that all stars form in embedded clusters is in agreement with observational data for the youngest stars (age $\lesssim 10$ Myr). In the $\Gamma$-$1$ scenario, the observed fraction of the youngest stars in clusters increases with the SFR only weakly; the increase is caused by the presence of more massive clusters in galaxies with higher SFRs, which release fewer stars to the field in proportion to their mass. The $\Gamma$-$1$ model yields a higher fraction of stars in clusters for older stars (age between $10$ and $300$ Myr) than what is observed. This discrepancy can be caused by interactions with molecular clouds.

16 pages, 9 figures, accepted to A&A

References in corpus (20)

• Binary interaction dominates the evolution of massive stars
• A comprehensive set of simulations studying the influence of gas expulsion on star cluster evolution
• What determines the density structure of molecular clouds ? A case study of Orion B with Herschel
• On the Density Distribution in Star-forming Interstellar Clouds
• The Spatial Structure of Young Stellar Clusters. I. Subclusters
• Star Cluster Demographics. I. A General Framework and Application to the Antennae Galaxies
• PeTar: a high-performance N-body code for modeling massive collisional stellar systems
• Molecular clouds have power-law probability distribution functions
• Hierarchical Star Formation in the Spiral Galaxy NGC 628
• The optimally-sampled galaxy-wide stellar initial mass function - Observational tests and the publicly available GalIMF code
• Dependency of dynamical ejections of O stars on the masses of very young star clusters
• The relationship between the prestellar core mass function and the stellar initial mass function
• The formation of NGC 3603 young starburst cluster: "prompt" hierarchical assembly or monolithic starburst?
• Praesepe (NGC 2632) and its tidal tails
• Stellar clusterings around "Isolated" Massive YSOs in the LMC
• Different Fates of Young Star Clusters After Gas Expulsion
• How fast do young star clusters expel their natal gas?: Estimating the upper limit of the gas expulsion time-scale
• A new method to create initially mass segregated star clusters in virial equilibrium
• How fast is mass-segregation happening in hierarchical formed embedded star clusters?
• A Census of Star Formation in the Outer Galaxy II: The GLIMPSE360 Field

Cited by in corpus (16)

• A Sun-like star orbiting a black hole
• Strong constraints on the gravitational law from $Gaia$ DR3 wide binaries
• The most massive stars in very young star clusters with a limited mass: Evidence favours significant self-regulation in the star formation processes
• Asymmetrical tidal tails of open star clusters: stars crossing their cluster's prah challenge Newtonian gravitation
• Pre-supernova feedback sets the star cluster mass function to a power law and reduces the cluster formation efficiency
• A tale of caution: the tails of NGC 752 are much longer than claimed
• The effect of the environment-dependent stellar initial mass function on the photometric properties of star-forming galaxies
• Fraction of Stars in Clusters for the LEGUS Dwarf Galaxies
• The spin, expansion and contraction of open star clusters
• Open star clusters and their asymmetrical tidal tails
• The galaxy-wide stellar initial mass function in the presence of cluster-to-cluster IMF variations
• A Tale of 3 Dwarfs: No Extreme Cluster Formation in Extreme Star-Forming Galaxies
• Stellar population synthesis models with a physically varying IMF
• Cluster aggregates surrounding Pismis 5 in the Vela Molecular Ridge
• Topography of the Young Galactic Disk: Spatial and Kinematic Patterns of the Clustered Star Formation in the Solar Neighborhood
• Clusters, Clumps, Dust, & Gas (CCDG) in NGC1614: Bench-marking Cluster Demographics in Extreme Systems