arXiv subjects

Nikos Prantzos

Publications and source records attributed to Nikos Prantzos.

At least 19 recordsLinked to original sources

arXiv2025

Recent star formation episodes in the Galaxy: impact on its chemical properties and the evolution of its abundance gradient

We investigate the chemical evolution of the Milky Way disc exploring various schemes of recent (last several Gyr) star formation episodes, as reported in recent observational works. We use a semi-analytical model with parametrized radial migration and we introduce gaussian star formation episodes constrained by those recent observations. We find significant impact of the star formation episodes on several observables, like the local age-metallicity and [alpha/Fe] vs metallicity relations, as well as the local stellar metallicity distribution or the existence of young [alpha/Fe]-rich stars. Moreover, we show that the recently found "wiggly" behaviour of the disk abundance gradient with age can be interpreted in terms of either star formation or infall episodes.

astro-ph.GA↗

arXiv2024

Evolution of lithium in the disc of the Galaxy and the role of novae

Lithium plays a crucial role in probing stellar physics and stellar and primordial nucleosynthesis, as well as the chemical evolution of our Galaxy. Stars are considered to be the main source of Li, still the identity of its primary stellar producer has long been a matter of debate. In light of recent theoretical and observational results, we investigate in this study the role of two candidate sources of Li enrichment in the Milky Way, namely AGB stars and, in particular, novae. We utilize a one-zone Galactic chemical evolution model to assess the viability of AGB stars and novae as stellar sources of Li. We use recent theoretical Li yields for AGB stars, while for novae we adopt observationally inferred Li yields and recently derived Delay Time Distributions (DTDs). Subsequently, we extend our analysis using a multi-zone model with radial migration to investigate spatial variations in the evolution of Li across the Milky Way disc and compare the results with observational data for field stars and open clusters. Our analysis shows that AGB stars fail by far to reproduce the meteoritic Li abundance. In contrast, novae appear as promising candidates within the adopted framework, allowing us to quantify the contribution of each Li source at Sun's formation and today. Our multi-zone model reveals the role of the differences in the DTDs of SN Ia and novae in shaping the evolution of Li in the various galactic zones. Its results are in fair agreement with the observational data for most open clusters, but small discrepancies appear in the outer disc.

astro-ph.GA↗

arXiv2024

Abundances of planetary nebulae and evolved stars: Iron and sulfur depletion, and carbon and nitrogen enrichment, in low- and intermediate-mass stellar populations in the Milky Way

We explore the elemental abundances in Galactic planetary nebulae (PNe) compared with those of their stellar progenitors (Red Giant Branch and Asymptotic Giant Branch, RGB and AGB, stars), to explore and quantify the expected -- i.e., due to AGB evolution or condensation onto grains -- differences. We gleaned the current literature for the nebular abundances while we used the APOGEE DR~17 survey data for the stellar sample. We examined the elements in common between the nebular and stellar samples, namely, C, N, O, Fe, and S. We confirm that iron in PNe is mostly entrapped in grains, with an average depletion $<$D[Fe/H]$>$=1.741$\pm$0.486 dex, and we disclose a weak correlation between iron depletion and the [O/H] abundance, D[Fe/H]$=(6.6003\pm2.443)\times{\rm [O/H]} +(1.972\pm0.199)$. Sulfur may also be mildly depleted in PNe, with $<$D[S/H]$>=0.179\pm0.291$ dex. We also found an indication of nitrogen enrichment for PNe $<$E[N/H]$>$=0.393$\pm$0.421 dex, with maximum enrichment (0.980$\pm$0.243) occurring for the PNe whose progenitors have gone through the HBB. The carbon enrichment is $<$E[C/H]$>$=0.332$\pm$0.460 dex when measured for the general PN populations. Our results will be relevant for future Galactic and extragalactic studies comparing nebular and stellar samples.

astro-ph.GA↗

arXiv2024

A coherent view of Li depletion and angular momentum transport to explain the Li plateau -- from Population II to Population I stars

Unraveling the cosmological Li problem - the discrepancy between Big Bang nucleosynthesis predictions and observed values in the Spite plateau - requires a comprehensive exploration of stellar evolution. In this study, we utilized the code STAREVOL to compute the stellar evolution models with atomic diffusion, rotation-induced processes, parametric turbulence, and additional viscosity. We calibrated the models to fit the abundance of Li in Population II stars selected from the GALAH DR3 spectroscopic survey and literature compilation based on their chemical composition. The calibration reveals the significance of parametric turbulence in counteracting atomic diffusion effects. These models predict the constancy of the Spite plateau as a function of $T_\mathrm{eff}$ and [Fe/H] which agrees with the observational trend found after a detailed selection of dwarf non-peculiar stars. Other dwarfs that lie below the Spite plateau are either CEMP or have other types of chemical peculiarities, reinforcing the notion of their environmental origin. The Li abundance near the Spite plateau of the most Fe-deficient star, J0023+0307, which is not CEMP, provides additional evidence for the stellar depletion solution of the Li cosmological problem. Also, our models predict a transition from Li constancy at low metallicities to dispersion at high metallicities which is seen in observations. In addition, we extend our analysis to include a comparison with observational data from the globular cluster NGC 6752, showcasing excellent agreement between model predictions and Li and Mg trends in post-turnoff stars. This opens avenues for refining the estimates of initial Li abundance in metal-rich globular clusters which would help to constrain Li evolution in the Milky Way.

astro-ph.SR↗

arXiv2023

The impact of rare events on the chemical enrichment in dwarf galaxies

In the environments where the abundance of heavy elements is low, rare events are expected to impact the chemical enrichment. Dwarf galaxies have small masses, low average metallicities and in general low star formation rates, and thus investigating the chemical enrichment provides understanding on the impact of each source of elements on the chemical abundance. Using a chemical evolution model in which the rarity is introduced, we investigate the impact of rare events on the chemical enrichment for Local Group dwarf galaxies. In the model, the occurrence of individual sources of elements is estimated with the star formation history derived by the colour-magnitude diagram. The abundance ratios of trans-iron elements to iron predicted by the model show the oscillation at the lowest metallicities because of the r-process events. In the case of a galaxy of a lower mass, the oscillation caused by neutron star mergers is also seen at higher metallicities, which suggests that the rarity can be important in lower-mass systems. Regarding the source of the chemical enrichment, we observe that the r-process sites seem to contribute more to the production of trans-iron elements at low metallicities, but massive stars of different rotating velocities also contribute to create part of the dispersion of the abundance ratios through the s-process. Both observational and theoretical data, including nucleosynthesis calculations and the chemical abundance of metal-poor stars, are needed to obtain deeper insights into the sources of the chemical enrichment at low metallicities.

astro-ph.GA↗

arXiv2023

The Missing Link: Testing Galactic Chemical Evolution Models with the First Multi-Isotopic Abundances in Solar Twin Stars

We present the first isotopic abundances of both $^{13}$CO and C$^{18}$O in solar twin stars and test the results against several galactic chemical evolution (GCE) models with different nucleosynthesis prescriptions. First, we compare M-band spectra from IRTF/iSHELL to synthetic spectra generated from custom solar atmosphere models using the PHOENIX atmosphere code. Next, we compare our calculated abundances to GCE models that consider isotopic yields from massive stars, asymptotic giant branch (AGB) stars and fast-rotating stars. The $^{12}$C/$^{13}$C ratios determined for this sample of solar twins are consistent with predictions from the selected GCE models; however, the $^{16}$O/$^{18}$O ratios tentatively contradict these predictions. This project constitutes the first in a stellar chemical abundance series seeking to: (1) support the James Webb Space Telescope (JWST) as it characterizes exoplanet atmospheres, interiors, and biosignatures by providing host star abundances (2) identify how unexplored stellar abundances reveal the process of galactic chemical evolution and correlate with star formation, interior, age, metallicity, and activity; and (3) provide improved stellar ages using stellar abundance measurements. By measuring elemental and isotopic abundances in a variety of stars, we not only supply refined host star parameters, but also provide the necessary foundations for complementary exoplanet characterization studies and ultimately contribute to the exploration of galactic, stellar, and planetary origins and evolution.

astro-ph.SR↗

arXiv2023

On the origin of the Galactic thin and thick discs, their abundance gradients and the diagnostic potential of their abundance ratios

Using a semi-analytical model of the evolution of the Milky Way, we show how secular evolution can create distinct overdensities in the phase space of various properties (e.g. age vs metallicity or abundance ratios vs age) corresponding to the thin and thick discs. In particular, we show how key properties of the Solar vicinity can be obtained by secular evolution, with no need for external or special events, like galaxy mergers or paucity in star formation. This concerns the long established double-branch behaviour of [alpha/Fe] vs metallicity and the recently found non-monotonic evolution of the stellar abundance gradient, evaluated at the birth radii of stars. We extend the discussion to other abundance ratios and we suggest a classification scheme, based on the nature of the corresponding yields (primary vs secondary or odd elements) and on the lifetimes of their sources (short-lived vs long-lived ones). The latter property is critical in determining the single- or double- branch behavior of an elementary abundance ratio in the Solar neighborhood. We underline the high diagnostic potential of this finding, which can help to separate clearly elements with sources evolving on different timescales and help determining the site of e.g. the r-process(es). We define the "abundance distance" between the thin and thick disc sequences as an important element for such a separation. We also show how the inside-out evolution of the Milky Way disc leads rather to a single-branch behavior in other disc regions.

astro-ph.GA↗

arXiv2023

Cosmic Radioactivity and Galactic Chemical Evolution

The description of the tempo-spatial evolution of the composition of cosmic gas on galactic scales is called 'modelling galactic chemical evolution'. It aims to use knowledge about sources of nucleosynthesis and how they change the composition of interstellar gas, following the formation of stars and the ejection of products from nuclear fusion during their evolution and terminating explosions. Sources of nucleosynthesis are diverse: Stars with hydrostatic nuclear burning eject some of the products, and core-collapse supernovae add ejecta. Binary interactions lead to sources such as thermonuclear supernovae and kilonovae. Tracing ejecta from sources, with their different frequencies and environments, through the interstellar medium and successive star formation cycles is the goal of model descriptions. A variety of formalisms exist, from analytical through semi-analytical, numerical or stochastic approaches, gradually making descriptions of compositional evolution of cosmic matter more realistic, teaching us about the astrophysical processes involved in this complex aspect of our universe. Radioactive isotopes add important ingredients to such modelling: The intrinsic clock of the radioactive decay process adds a new aspect to the modelling algorithms that leads to different constraints on the important unknowns of star formation activity and interstellar transports. Several prominent examples illustrate how modelling the abundances of radioactive isotopes and their evolution have resulted in new lessons; among these are the galaxy-wide distribution of 26Al and 60Fe, the radioactive components of cosmic rays, the interpretations of terrestrial deposits of 60Fe and 244Pu, and the radioactive-decay daughter isotopes that were found in meteorites and characterise the birth environment of our solar system.

astro-ph.GA↗

arXiv2022

Evidence of Deep Mixing in IRS 7, a Cool Massive Supergiant Member of the Galactic Nuclear Star Cluster

The center of the Milky Way contains stellar populations spanning a range in age and metallicity, with a recent star formation burst producing young and massive stars. Chemical abundances in the most luminous stellar member of the Nuclear Star Cluster (NSC), IRS 7, are presented for $^{19}$F, $^{12}$C, $^{13}$C, $^{14}$N, $^{16}$O, $^{17}$O, and Fe from an LTE analysis based on spherical modeling and radiative transfer with a 25M$_{\odot}$ model atmosphere, whose chemistry was tailored to the derived photospheric abundances. We find IRS 7 to be depleted heavily in both $^{12}$C (~-0.8 dex) and $^{16}$O (~-0.4 dex), while exhibiting an extremely enhanced $^{14}$N abundance (~+1.1 dex), which are isotopic signatures of the deep mixing of CNO-cycled material to the stellar surface. The $^{19}$F abundance is also heavily depleted by ~1 dex relative to the baseline fluorine of the Nuclear Star Cluster, providing evidence that fluorine along with carbon constrain the nature of the deep mixing in this very luminous supergiant. The abundances of the minor isotopes $^{13}$C and $^{17}$O are also derived, with ratios of $^{12}$C/$^{13}$C~5.3 and $^{16}$O/$^{17}$O~525. The derived abundances for IRS 7, in conjunction with previous abundance results for massive stars in the NSC, are compared with rotating and non-rotating models of massive stars and it is found that the IRS 7 abundances overall follow the behavior predicted by stellar models. The depleted fluorine abundance in IRS 7 illustrates, for the first time, the potential of using the $^{19}$F abundance as a mixing probe in luminous red giants.

astro-ph.SR↗

arXiv2022

Fluorine Abundances in the Galactic Nuclear Star Cluster

Abundances of fluorine ($^{19}$F), as well as isotopic ratios of $^{16}$O/$^{17}$O, are derived in a sample of luminous young ($\sim$10$^{7}$--10$^{8}$ yrs) red giants in the Galactic center (with galactocentric distances ranging from 0.6--30 pc), using high-resolution infrared spectra and vibration-rotation lines of H$^{19}$F near $\lambda$2.3$\mu$m. Five of the six red giants are members of the Nuclear star cluster that orbits the central supermassive black hole. Previous investigations of the chemical evolution of $^{19}$F in Galactic thin and thick disk stars have revealed that the nucleosynthetic origins of $^{19}$F may be rather complex, resulting from two, or more, astrophysical sites; fluorine abundances behave as a primary element with respect to Fe abundances for thick disk stars and as a secondary element in thin disk stars. The Galactic center red giants analyzed fall within the thin disk relation of F with Fe, having near-solar, to slightly larger, abundances of Fe ($<$[Fe/H]$>$=+0.08$\pm$0.04), with a slight enhancement of the F/Fe abundance ratio ($<$[F/Fe]$>$=+0.28$\pm$0.17). In terms of their F and Fe abundances, the Galactic center stars follow the thin disk population, which requires an efficient source of $^{19}$F that could be the winds from core-He burning Wolf Rayet stars, or thermally-pulsing AGB stars, or a combination of both. The observed increase of [F/Fe] with increasing [Fe/H] found in thin disk and Galactic center stars is not predicted by any published chemical evolution models that are discussed, thus a quantitative understanding of yields from the various possible sources of $^{19}$F remains unknown.

astro-ph.GA↗

arXiv2021

The Radioactive Nuclei $^{\textbf{26}}$Al and $^{\textbf{60}}$Fe in the Cosmos and in the Solar System

The cosmic evolution of the chemical elements from the Big Bang to the present time is driven by nuclear fusion reactions inside stars and stellar explosions. A cycle of matter recurrently re-processes metal-enriched stellar ejecta into the next generation of stars. The study of cosmic nucleosynthesis and of this matter cycle requires the understanding of the physics of nuclear reactions, of the conditions at which the nuclear reactions are activated inside the stars and stellar explosions, of the stellar ejection mechanisms through winds and explosions, and of the transport of the ejecta towards the next cycle, from hot plasma to cold, star-forming gas. Due to the long timescales of stellar evolution, and because of the infrequent occurrence of stellar explosions, observational studies are challenging. Due to their radioactive lifetime of million years, the 26Al and 60Fe isotopes are suitable to characterise simultaneously the processes of nuclear fusion reactions and of interstellar transport. We describe and discuss the nuclear reactions involved in the production and destruction of 26Al and 60Fe, the key characteristics of the stellar sites of their nucleosynthesis and their interstellar journey after ejection from the nucleosynthesis sites. We connect the theoretical astrophysical aspects to the variety of astronomical messengers, from stardust and cosmic-ray composition measurements, through observation of gamma rays produced by radioactivity, to material deposited in deep-sea ocean crusts and to the inferred composition of the first solids that have formed in the Solar System. We show that considering measurements of the isotopic ratio of 26Al to 60Fe eliminate some of the unknowns when interpreting astronomical results, and discuss the lessons learned from these two isotopes on cosmic chemical evolution.

astro-ph.HE↗

arXiv2021

Neutron star mergers as the astrophysical site of the r-process in the Milky Way and its satellite galaxies

Recent progress of nucleosynthesis work as well as the discovery of a kilonova associated with the gravitational-wave source GW170817 indicates that neutron star mergers (NSM) can be a site of the r-process. Several studies of galactic chemical evolution, however, have pointed out inconsistencies between this idea and the observed stellar abundance signatures in the Milky Way: (a) the presence of Eu at low (halo) metallicity and (b) the descending trend of Eu/Fe at high (disc) metallicity. In this study, we explore the galactic chemical evolution of the Milky Way's halo, disc and satellite dwarf galaxies. Particular attention is payed to the forms of delay-time distributions for both type Ia supernovae (SN Ia) and NSMs. The Galactic halo is modeled as an ensemble of independently evolving building-block galaxies with different masses. The single building blocks as well as the disc and satellite dwarfs are treated as well-mixed one-zone systems. Our results indicate that the aforementioned inconsistencies can be resolved and thus NSMs can be the unique r-process site in the Milky Way, provided that the delay-time distributions satisfy the following conditions: (i) a long delay (~1 Gyr) for the appearance of the first SN Ia (or a slow early increase of its number) and (ii) an additional early component providing >~ 50% of all NSMs with a delay of ~0.1 Gyr. In our model, r-process-enhanced and r-process-deficient stars in the halo appear to have originated from ultra-faint dwarf-sized and massive building blocks, respectively. Our results also imply that the natal kicks of binary neutron stars have a little impact on the evolution of Eu in the disc.

astro-ph.GA↗

arXiv2020

A probabilistic analysis of the Fermi paradox in terms of the Drake formula: the role of the L factor

In evaluating the number of technological civilizations N in the Galaxy through the Drake formula, emphasis is mostly put on the astrophysical and biotechnological factors describing the emergence of a civilization and much less on its the lifetime, which is intimately related to its demise. It is argued here that this factor is in fact the most important regarding the practical implications of the Drake formula, because it determines the maximal extent of the "sphere of influence" of any technological civilization. The Fermi paradox is studied in the terms of a simplified version of the Drake formula, through Monte Carlo simulations of N civilizations expanding in the Galaxy during their space faring lifetime L. In the framework of that scheme, the probability of "direct contact" is determined as the fraction of the Galactic volume occupied collectively by the "spheres of influence" of N civilizations. The results of the analysis are used to determine regions in the parameter space where the Fermi paradox holds. It is argued that in a large region of the diagram the corresponding parameters suggest rather a "weak" Fermi paradox. Future research may reveal whether a "strong" paradox holds in some part of the parameter space. Finally, it is argued that the value of N is not bound by N=1 from below, contrary to what is usually assumed, but it may have a statistical interpretation.

physics.pop-ph↗

arXiv2019

Positron Annihilation in the Galaxy

The 511 keV line from positron annihilation in the Galaxy was the first $\gamma$-ray line detected to originate from outside our solar system. Going into the fifth decade since the discovery, the source of positrons is still unconfirmed and remains one of the enduring mysteries in $\gamma$-ray astronomy. With a large flux of $\sim$10$^{-3}$ $\gamma$/cm$^{2}$/s, after 15 years in operation INTEGRAL/SPI has detected the 511 keV line at $>50\sigma$ and has performed high-resolution spectral studies which conclude that Galactic positrons predominantly annihilate at low energies in warm phases of the interstellar medium. The results from imaging are less certain, but show a spatial distribution with a strong concentration in the center of the Galaxy. The observed emission from the Galactic disk has low surface brightness and the scale height is poorly constrained, therefore, the shear number of annihilating positrons in our Galaxy is still not well know. Positrons produced in $\beta^+$-decay of nucleosynthesis products, such as $^{26}$Al, can account for some of the annihilation emission in the disk, but the observed spatial distribution, in particular the excess in the Galactic bulge, remains difficult to explain. Additionally, one of the largest uncertainties in these studies is the unknown distance that positrons propagate before annihilation. In this paper, we will summarize the current knowledge base of Galactic positrons, and discuss how next-generation instruments could finally provide the answers.

astro-ph.HE↗

arXiv2018

Stochastic Chemical Evolution of Galactic Subhalos and the Origin of r-Process Elements

Mergers of compact binaries (of a neutron star and another neutron star or a black hole, NSMs) are suggested to be the promising astrophysical site of the r-process. While the average coalescence timescale of NSMs appears to be > 100 Myr, most of previous chemical evolution models indicate that the observed early appearance and large dispersion of [r/Fe] in Galactic halo stars at [Fe/H] < -2.5 favors shorter coalescence times of 1-10 Myr. We argue that this is not the case for the models assuming the formation of the Galactic halo from clustering of subhalos with different star formation histories as suggested by Ishimaru et al. (2015). We present a stochastic chemical evolution model of the subhalos, in which the site of the r-process is assumed to be mainly NSMs with a coalescence timescale of 100 Myr. In view of the scarcity of NSMs, their occurrence in each subhalo is computed with a Monte Carlo method. Our results show that the less massive subhalos evolve at lower metallicities and generate highly r-process-enhanced stars. An assembly of these subhalos leaves behind the large star-to-star scatters of [r/Fe] in the Galactic halo as observed. However, the observed scatters of [Sr/Ba] at low metallicities indicate the presence of an additional site that partially contributes to the enrichment of light neutron-capture elements such as Sr. The high enhancements of [r/Fe] at low metallicities found in our low-mass subhalo models also qualitatively reproduce the abundance signatures of the stars in the recently discovered ultra-faint dwarf galaxy Reticulum II. Therefore, our results suggest NSMs as the dominant sources of r-process elements in the Galactic halo.

astro-ph.GA↗

arXiv2016

On Potassium and Other Abundance Anomalies of Red Giants in NGC 2419

Globular clusters are of paramount importance for testing theories of stellar evolution and early galaxy formation. Strong evidence for multiple populations of stars in globular clusters derives from observed abundance anomalies. A puzzling example is the recently detected Mg-K anticorrelation in NGC 2419. We perform Monte Carlo nuclear reaction network calculations to constrain the temperature-density conditions that gave rise to the elemental abundances observed in this elusive cluster. We find a correlation between stellar temperature and density values that provide a satisfactory match between simulated and observed abundances in NGC 2419 for all relevant elements (Mg, Si, K, Ca, Sc, Ti, and V). Except at the highest densities ($\rho \gtrsim 10^8$~g/cm$^3$), the acceptable conditions range from $\approx$ $100$~MK at $\approx$ $10^8$~g/cm$^3$ to $\approx$ $200$~MK at $\approx$ $10^{-4}$~g/cm$^3$. This result accounts for uncertainties in nuclear reaction rates and variations in the assumed initial composition. We review hydrogen burning sites and find that low-mass stars, AGB stars, massive stars, or supermassive stars cannot account for the observed abundance anomalies in NGC 2419. Super-AGB stars could be viable candidates for the polluter stars if stellar model parameters can be fine-tuned to produce higher temperatures. Novae, either involving CO or ONe white dwarfs, could be interesting polluter candidates, but a current lack of low-metallicity nova models precludes firmer conclusions. We also discuss if additional constraints for the first-generation polluters can be obtained by future measurements of oxygen, or by evolving models of second-generation low-mass stars with a non-canonical initial composition.

astro-ph.SR↗

arXiv2015

Neutron Star Mergers as the Origin of r-Process Elements in the Galactic Halo Based on the Sub-halo Clustering Scenario

Binary mergers (NSMs) of double neutron star (and black hole-neutron star) systems are suggested to be major sites of r-process elements in the Galaxy by recent hydrodynamical and nucleosynthesis studies. It has been pointed out, however, that the estimated long lifetimes of neutron star binaries are in conflict with the presence of r-process-enhanced halo stars at metallicities as low as [Fe/H] ~ -3. To resolve this problem, we examine the role of NSMs in the early Galactic chemical evolution on the assumption that the Galactic halo was formed from merging sub-halos. We present simple models for the chemical evolution of sub-halos with total final stellar masses between 10^4 M_solar and 2 x 10^8 M_solar. Typical lifetimes of compact binaries are assumed to be 100 Myr (for 95% of their population) and 1 Myr (for 5%), according to recent binary population synthesis studies. The resulting metallcities of sub-halos and their ensemble are consistent with the observed mass-metallicity relation of dwarf galaxies in the Local Group, and the metallicity distribution of the Galactic halo, respectively. We find that the r-process abundance ratios [r/Fe] start increasing at [Fe/H] <= -3 if the star formation efficiencies are smaller for less massive sub-halos. In addition, the sub-solar [r/Fe] values (observed as [Ba/Fe] ~ -1.5 for [Fe/H] < -3) are explained by the contribution from the short-lived (~1 Myr) binaries. Our results indicate that NSMs may have a substantial contribution to the r-process element abundances throughout the Galactic history.

astro-ph.GA↗

arXiv2013

Superbubble dynamics in globular cluster infancy II. Consequences for secondary star formation in the context of self-enrichment via fast rotating massive stars

The self-enrichment scenario for globular clusters (GC) requires large amounts of residual gas after the initial formation of the first stellar generation. Recently, Krause et al. (2012) found that supernovae may not be able to expel that gas, as required to explain their present day gas-free state, and suggested that a sudden accretion on to the dark remnants, at a stage when type II supernovae have ceased, may plausibly lead to fast gas expulsion. Here, we explore the consequences of these results for the self-enrichment scenario via fast rotating massive stars (FRMS). We analyse the interaction of FRMS with the intra-cluster medium (ICM), in particular where, when and how the second generation of stars may form. From the results, we develop a timeline of the first approximately 40 Myr of GC evolution. The results of Paper I imply three phases during which the ICM is in a fundamentally different state, namely the wind bubble phase (lasting 3.5 to 8.8 Myr), the supernova phase (lasting 26.2 to 31.5 Myr), and the dark remnant accretion phase (lasting 0.1 to 4 Myr): (i) Quickly after the first generation massive stars have formed, stellar wind bubbles compress the ICM into thin filaments. No stars may form in the normal way during this phase, due to the high Lyman-Werner flux density. If the first generation massive stars have however equatorial ejections, as we proposed in the FRMS scenario, accretion may resume in the shadow of the equatorial ejecta. The second generation stars may then form due to gravitational instability in these discs that are fed by both the FRMS ejecta and pristine gas. [...]

astro-ph.GA↗