scholarly journals Realistic modelling of wind and supernovae shocks in star clusters: addressing 22Ne/20Ne and other problems in Galactic cosmic rays

2020 ◽  
Vol 493 (3) ◽  
pp. 3159-3177 ◽  
Author(s):  
Siddhartha Gupta ◽  
Biman B Nath ◽  
Prateek Sharma ◽  
David Eichler
Keyword(s):  
Massive Star ◽  
Star Clusters ◽  
Cosmic Ray ◽  
Mass Function ◽  
Galactic Cosmic Rays ◽  
Star Cluster ◽  
Stellar Winds ◽  
Isotopic Abundances ◽  
Γ Ray ◽  
Massive Clusters

ABSTRACT Cosmic ray (CR) sources leave signatures in the isotopic abundances of CRs. Current models of Galactic CRs that consider supernovae (SNe) shocks as the main sites of particle acceleration cannot satisfactorily explain the higher 22Ne/20Ne ratio in CRs compared to the interstellar medium. Although stellar winds from massive stars have been invoked, their contribution relative to SNe ejecta has been taken as a free parameter. Here, we present a theoretical calculation of the relative contributions of wind termination shocks (WTSs) and SNe shocks in superbubbles, based on the hydrodynamics of winds in clusters, the standard stellar mass function, and stellar evolution theory. We find that the contribution of WTSs towards the total CR production is at least $25{{\ \rm per\ cent}}$, which rises to $\gtrsim 50{{\ \rm per\ cent}}$ for young (≲10 Myr) clusters, and explains the observed 22Ne/20Ne ratio. We argue that since the progenitors of apparently isolated supernovae remnants (SNRs) are born in massive star clusters, both WTS and SNe shocks can be integrated into a combined scenario of CRs being accelerated in massive clusters. This scenario is consistent with the observed ratio of SNRs to γ-ray bright (Lγ ≳ 1035 erg s−1) star clusters, as predicted by star cluster mass function. Moreover, WTSs can accelerate CRs to PeV energies, and solve other long-standing problems of the standard SN paradigm of CR acceleration.

scholarly journals Modeling of cosmic ray 22Ne-enrichment in compact star clusters

2021 ◽  
Vol 2103 (1) ◽  
pp. 012008
Author(s):  
M E Kalyashova ◽  
A M Bykov
Keyword(s):  
Massive Star ◽  
Isotopic Ratio ◽  
Compact Star ◽  
Star Clusters ◽  
Cosmic Ray ◽  
Rotation Velocity ◽  
Mass Function ◽  
Galactic Cosmic Rays ◽  
Initial Mass Function ◽  
The Impact

Abstract 22Ne/20Ne isotopic ratio is found to be about 5 times higher in Galactic cosmic rays (GCRs) than in the solar wind. In this paper we develop the hypothesis that the 22Ne overabundance in CRs is generated in compact massive star clusters which contain populations of Wolf-Rayet stars. Winds of Wolf-Rayet stars are considered to have high content of 22Ne. We assume that particle acceleration occurs on the ensemble of strong shocks from the massive stars’ winds. We present a model of cosmic ray enrichment with 22Ne, adding isotopic yields from supernovae and taking into account the acceleration efficiency during the lifetime of the stars. The impact of the parameters (the initial mass function in the cluster, rotation velocity, black hole cut-off mass) is discussed. The energy balance for our model is calculated.

scholarly journals The life and death of star clusters

2006 ◽  
Vol 2 (S237) ◽  
pp. 222-229 ◽  
Author(s):  
B. C. Whitmore
Keyword(s):  
Massive Star ◽  
Cluster Formation ◽  
Star Clusters ◽  
Mass Function ◽  
Initial Mass Function ◽  
Merging Galaxies ◽  
Life And Death ◽  
Large Numbers ◽  
Super Star Clusters ◽  
Massive Clusters

AbstractIt is generally believed that most stars are born in groups and clusters, rather than in the field. It has also been demonstrated that merging galaxies produce large numbers of young massive star clusters, sometimes called super star clusters. Hence, understanding what triggers the formation of these young massive clusters may provide important information about what triggers the formation of stars in general. In recent years it has become apparent that most clusters do not survive more than ≈10 Myr (i.e., “infant mortality”). Hence, it is just as important to understand the disruption of star clusters as it is to understand their formation if we want to understand the demographics of both star clusters and field stars. This talk will first discuss what triggers star cluster formation in merging galaxies (primarily in the Antennae galaxies), will then demonstrate that most of the faint objects detected in the Antennae are clusters rather than individual stars (which shows that the initial mass function was a power law rather than a Gaussian), and will then outline a general framework designed to empirically fit observations of both star clusters and field stars in a wide variety of galaxies from mergers to quiescent spirals.

scholarly journals Mid-infrared [NeII] Imaging of Young Massive Star Clusters Near Galactic Nuclei

2015 ◽  
Vol 12 (S316) ◽  
pp. 161-162
Author(s):  
Sherry C. C. Yeh ◽  
Chao-Wei Tsai ◽  
Thomas R. Geballe ◽  
Cinthya N. Herrera
Keyword(s):  
Environmental Effects ◽  
Massive Star ◽  
Cluster Formation ◽  
Star Clusters ◽  
Galactic Nuclei ◽  
Mass Function ◽  
Mid Infrared ◽  
Ngc 6946 ◽  
Formation Efficiency ◽  
Massive Clusters

AbstractWe investigate the formation of young massive clusters near the nuclei in NGC 6946, IC 342, Maffei II, and NGC 7714, using ground-based mid-infrared [NeII] imaging. We derive the cluster formation efficiency and cluster mass function, and the results suggest that environmental effects on YMC formation may not be significant.

scholarly journals Super massive star clusters: from superwinds to a cooling catastrophe and the re-processing of the injected gas

2006 ◽  
Vol 2 (S237) ◽  
pp. 242-245
Author(s):  
S. Silich ◽  
G. Tenorio-Tagle ◽  
C. Muñoz-Tuñón ◽  
J. Palouš
Keyword(s):  
Positive Feedback ◽  
Massive Star ◽  
Threshold Energy ◽  
Star Clusters ◽  
Star Cluster ◽  
Stellar Winds ◽  
Star Forming ◽  
Radiative Regime

AbstractDifferent hydrodynamic regimes for the gaseous outflows generated by multiple supernovae explosions and stellar winds occurring within compact and massive star clusters are discussed. It is shown that there exists the threshold energy that separates clusters whose outflows evolve in the quasi-adiabatic or radiative regime from those within which catastrophic cooling and a positive feedback star-forming mode sets in. The role of the surrounding ISM and the observational appearance of the star cluster winds evolving in different hydrodynamic regimes are also discussed.

scholarly journals Massive star clusters in galaxies

2010 ◽  
Vol 368 (1913) ◽  
pp. 889-906 ◽  
Author(s):  
William E. Harris
Keyword(s):  
Recent Work ◽  
Globular Clusters ◽  
Evolutionary History ◽  
Massive Star ◽  
Star Clusters ◽  
Star Cluster ◽  
Cluster System ◽  
History Of ◽  
Review Current

The ensemble of all star clusters in a galaxy constitutes its star cluster system . In this review, the focus of the discussion is on the ability of star clusters, particularly the systems of old massive globular clusters (GCs), to mark the early evolutionary history of galaxies. I review current themes and key findings in GC research, and highlight some of the outstanding questions that are emerging from recent work.

scholarly journals The influence of feedback from massive stars on the formation and emergence of massive clusters

2015 ◽  
Vol 12 (S316) ◽  
pp. 177-183
Author(s):  
James E. Dale
Keyword(s):  
Large Scale ◽  
Massive Star ◽  
Massive Stars ◽  
Cluster Structure ◽  
Star Clusters ◽  
Stellar Feedback ◽  
Making Sense ◽  
Formation Efficiency ◽  
Massive Clusters ◽  
Made In

AbstractMassive star clusters are of fundamental importance both observationally, since they are visible at such great distances, and theoretically, because of their influence on the large–scale ISM. Understanding stellar feedback is a prerequisite for making sense of their formation and early evolution, since feedback influences cluster structure, star formation efficiency, and sets the timescales on which clusters emerge from their parent clouds to become optically visible. I review the progress made in understanding these issues from a numerical perspective.

scholarly journals Young and intermediate-age massive star clusters

2010 ◽  
Vol 368 (1913) ◽  
pp. 867-887 ◽  
Author(s):  
Søren S. Larsen
Keyword(s):  
Star Formation ◽  
Star Clusters ◽  
Mass Function ◽  
Starburst Galaxies ◽  
Open Clusters ◽  
High Mass ◽  
Current Evidence ◽  
Power Law Distribution ◽  
Low Mass ◽  
Massive Clusters

An overview of our current understanding of the formation and evolution of star clusters is given, with the main emphasis on high-mass clusters. Clusters form deeply embedded within dense clouds of molecular gas. Left-over gas is cleared within a few million years and, depending on the efficiency of star formation, the clusters may disperse almost immediately or remain gravitationally bound. Current evidence suggests that a small percentage of star formation occurs in clusters that remain bound, although it is not yet clear whether this fraction is truly universal. Internal two-body relaxation and external shocks will lead to further, gradual dissolution on time scales of up to a few hundred million years for low-mass open clusters in the Milky Way, while the most massive clusters (>10 5  M ⊙ ) have lifetimes comparable to or exceeding the age of the Universe. The low-mass end of the initial cluster mass function is well approximated by a power-law distribution, , but there is mounting evidence that quiescent spiral discs form relatively few clusters with masses M >2×10 5  M ⊙ . In starburst galaxies and old globular cluster systems, this limit appears to be higher, at least several ×10 6  M ⊙ . The difference is likely related to the higher gas densities and pressures in starburst galaxies, which allow denser, more massive giant molecular clouds to form. Low-mass clusters may thus trace star formation quite universally, while the more long-lived, massive clusters appear to form preferentially in the context of violent star formation.

scholarly journals The Influence of Gas Expulsion on the Evolution of Star Clusters

2007 ◽  
Vol 3 (S246) ◽  
pp. 36-40
Author(s):  
H. Baumgardt ◽  
P. Kroupa
Keyword(s):  
Globular Clusters ◽  
Milky Way ◽  
Three Dimensional ◽  
Star Clusters ◽  
Dynamical Evolution ◽  
Mass Function ◽  
Star Cluster ◽  
Dissolution Mechanism ◽  
Large Set ◽  
Cluster Systems

AbstractWe present new results on the dynamical evolution and dissolution of star clusters due to residual gas expulsion and the effect this has on the mass function and other properties of star cluster systems. To this end, we have carried out a large set of N-body simulations, varying the star formation efficiency, gas expulsion time scale and strength of the external tidal field, obtaining a three-dimensional grid of models which can be used to predict the evolution of individual star clusters or whole star cluster systems by interpolating between our runs. When applied to the Milky Way globular cluster system, we find that gas expulsion is the main dissolution mechanism for star clusters, destroying about 80% of all clusters within a few 10s of Myers. Together with later dynamical evolution, it seems possible to turn an initial power-law mass function into a log-normal one with properties similar to what has been observed for the Milky Way globular clusters.

scholarly journals MOCCA-SURVEY Database I: Dissolution of tidally filling star clusters harboring black hole subsystem

2019 ◽  
Vol 14 (S351) ◽  
pp. 438-441 ◽  
Author(s):  
Mirek Giersz ◽  
Abbas Askar ◽  
Long Wang ◽  
Arkadiusz Hypki ◽  
Agostino Leveque ◽  
...  
Keyword(s):  
Black Hole ◽  
Star Clusters ◽  
Mass Function ◽  
Stellar Mass ◽  
Star Cluster ◽  
Initial Mass Function ◽  
Initial Mass ◽  
Dissolution Process ◽  
Dissolution Mechanism ◽  
Dynamical Equilibrium

AbstractWe investigate the dissolution process of star clusters embedded in an external tidal field and harboring a subsystem of stellar-mass black hole. For this purpose we analyzed the MOCCA models of real star clusters contained in the Mocca Survey Database I. We showed that the presence of a stellar-mass black hole subsystem in tidally filling star cluster can lead to abrupt cluster dissolution connected with the loss of cluster dynamical equilibrium. Such cluster dissolution can be regarded as a third type of cluster dissolution mechanism. We additionally argue that such a mechanism should also work for tidally under-filling clusters with a top-heavy initial mass function.

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