Corinne Charbonnel
Did supermassive stars shape the properties of the multiple stellar populations in proto-globular clusters? From the local to the early universe, and back
Globular clusters (GCs) are fascinating objects nearly as old as the Universe that provide insight on a large variety of astrophysical and cosmological processes. However, their formation and their early and long-term evolution are far from being understood. In particular, the classical paradigm describing GCs as large systems of coeval stars formed out of chemically homogeneous material has been definitively swept away by high-precision spectroscopic and deep photometric observations. Data have provided undisputed evidence that GCs harbor multiple stellar populations with very unique chemical properties, which formed during the very first millions of years of their host GC evolution. Recently, JWST opened a new window on GC in their infancy with the discovery of potential globular proto-clusters in high-redshift galaxies, providing new clues to the origin of their multiple stellar populations. In this talk, I will briefly review the properties of these multiple populations, and I will describe the supermassive star scenario that we have proposed to describe their formation.
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Diasuke Toyouchi
Toward understanding the coevolution of galaxies and supermassive black holes
Recent advancements in semi-analytical models and numerical fluid simulations have deepened our understanding of the formation of seed black holes (BHs) and their subsequent mass growth in the early universe. The next crucial challenge is to link the mass growth of these seed BHs with the evolution of the proto-galaxies that host them. The latest observations from the James Webb Space Telescope (JWST) have reported the presence of quasars at z > 5 that are overmassive to the local empirical relation. However, Recent cosmological galaxy formation simulations have been unable to explain the existence of such overmassive quasars, indicating an inadequate understanding of the gas supply processes from galaxy scales to the central BHs. In this presentation, I will review the current situation, especially from the theoretical side, and discuss the future challenges in understanding the coevolution processes of galaxies and supermassive BHs.
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Dan Whalen
The Turbulent Origins of the First Quasars
Direct collapse of atomically-cooled gas into supermassive stars and
DCBHs is usually invoked as the origin of the first quasars in the
Universe at z > 7. However, it is difficult to pair the unusual,
finely-tuned environments thought to be required for DCBH formation
with the rare halos required to rapidly fuel the growth of the BH to
10^9 solar masses by z ~ 7. We have now shown with new
high-resolution cosmological simulations that such halos form their
own DCBHs without the need for UV backgrounds, supersonic baryon
streaming motions, or even atomic cooling. The strong accretion
streams that rapidly grow the halo drive highly supersonic turbulence
in its gas, preventing it from collapsing into stars even with strong
H_2 cooling. When the halo mass exceeds a few 10^7 solar masses,
gravity overcomes the turbulence, causing catastrophic baryon collapse
and the formation of DCBHs with masses of a few 10^4 solar masses.
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Erin Higgins
Title: Nucleosynthesis and wind yields of Very Massive Stars
Abstract: The most massive stars provide an essential source of recycled material for young clusters and galaxies. While very massive stars (VMS, M>100 M) are relatively rare compared to O stars, they lose disproportionately large amounts of mass already from the onset of core H-burning. In this talk, I will discuss the impact of stellar wind yields from VMS, calculated for a wide range of masses (50-500Msun) at solar metallicity, using the MESA stellar evolution code. We find that for VMS, 95% of the total wind yields are produced already on the main sequence, while only ∼ 5% is supplied by the post-main sequence. This implies that VMS are the primary source of 26-Al and could be responsible for the observed Galactic 26-Al enrichment. Interestingly, we find that 200Msun stars eject 100 times more of each heavy element in their winds than 50Msun stars, and even when weighted by an IMF their wind contribution is still an order of magnitude higher than that of a 50 M star.
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Hideyuki Saio
Title: Instabilities in Super Massive Stars
Abstract:
A supermassive black hole in the early universe is possibly formed through the general relativistic (GR) collapse of a supermassive star formed by a rapid mass accretion. Previous studies also indicate that radial pulsations are thermally excited in supermassive stars before the GR instability occurs. I will talk about results of normal-mode analyses applied to Geneva models to study the GR instability as well as the pulsational instability.
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John Regan
Title: Forming Super Massive Stars in Cosmological Simulations
Abstract: Massive Black Holes with masses in excess of one million solar
masses have been observed with JWST as far back at z = 10. Moreover,
these MBHs appear overly massive compared to their host galaxy. In this
talk I will describe the Renaissance suite of cosmological simulations
and in particular the formation of very/super massive stars from
cosmological initial conditions. These stars require somewhat unusual
environemental conditions in which to form but I will also show that
their number densities may be higher than previously thought. I will
also show that light seeds (black holes born from 'normal' PopIII stars)
may have a hard time achieving the necessary growth to explain high-z
massive black holes making SMSs promising candidates.
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John Wise
Title: Supermassive stars and massive black hole seeds in rapidly growing minihalos
Abstract:
I will present results from a suite of cosmological radiation hydrodynamics simulations that focus on massive metal-free stars and the first galaxies. We find that a rare set of galaxies initially form a cluster of (super)massive stars, resulting in several intermediate mass black holes before any metal-enriched star formation. Such behavior occurs in halos that grow rapidly, suppressing star formation in minihalos through dynamical heating. I will also present preliminary results of a probabilistic DCBH seeding model trained on small-scale, halo, and large-scale characteristics of the first galaxies and their black holes from this simulation suite.
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Jorick Vink
Mass Loss History of Very Massive Stars
Is there an upper limit to stellar mass and what physics sets this limit?
In this talk I discuss why metallicity-dependent radiation-driven winds are one of the prime candidates setting the stellar upper-mass limit. I present a new mass-loss prescription for very massive stars (VMS) in the 100-1000 Msun range, based on the transition mass-loss point, where optically-thin winds transition to optically-thick winds undergoing vigorous multiple scattering. Using a 1D stellar evolution code (MESA) I show how their extreme mass-loss history causes VMS to "evaporate" during the main sequence, as they drop steeply in luminosity, evolving vertically in the HR diagram, naturally explaining their observed narrow range of temperatures. Finally, I suggest that the slower winds from VMS are an important source of self-enrichment in globular clusters and I estimate that the huge amounts of Nitrogen present in star-forming galaxies at high redshift such as GN z-11 could also result from VMSs.
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Kazutaka Kimura
Title:
Co-evolution of Accreting Protostar and Circumstellar Disk in 3D : Evolution toward the Supermassive Star Formation
Abstract:
Direct Collapse (DC) scenario is one possible pathway to form supermassive black holes in the high-redshift universe. In this scenario, protostars grow in mass with very high accretion rates of ~0.1-1 Msun/yr. If the accretion continues for ~1 Myr, protostars evolve into supermassive stars (SMSs), which is the progenitor of massive seed black holes. Whether SMSs are formed depends on the protostellar evolution under such high accretion rates because resulting protostellar radiation and rotation may prevent the accretion. Although the main methodology for studying their evolution is a simplified one-dimensional (1D) model so far (e.g. Hosokawa et al. 2012; Haemmerlé et al. 2018), primordial gas clouds generally have rotation and turbulence, which lead to multi-dimensional structure.
In this work, we calculate the protostellar evolution in the DC scenario with high-resolution three-dimensional (3D) radiation-hydrodynamic simulation resolving its interior. In our previous paper, we followed the early evolution until 10 years after the protostellar birth (Kimura et al. 2023). In this talk, we show the results from the longer-term calculation following the evolution for several hundreds of years after the protostellar birth. We demonstrate that a swollen and fast-rotating protostar emerges as predicted by previous 1D models. Moreover, the initial angular momentum of the cloud leads to the formation of the circumstellar disk. The disk develops spiral arms and frequently fragments due to the gravitational instability. We discuss the difference between protostellar evolution in our 3D simulation and previous 1D models, and its influence on the formation of SMSs.
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Kohei Inayoshi
Title: The assembly of the first massive black holes and the prospects of JWST observations
Abstract: The James Webb Space Telescope (JWST) is unveiling the early growth of supermassive black holes (BHs) in the first galaxies. The existence of supermassive massive BHs observed when the universe was younger than one billion years strongly constrains their formation pathway and provides a crucial hint to understanding the coevolution between BHs and galaxies. In this talk, I will review the physical mechanisms that promote the rapid assembly and growth of seed BHs in early protogalaxies, and discuss the recent progress of hunting for low-luminosity active galactic nuclei (low-mass BHs) at z=4-11 using JWST NIRSpec/NIRCam observations. I will further discuss the characteristics nature of radiation spectra from those early BHs and their progenitors.
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Laura Ramirez
Globular clusters (GCs) exhibit peculiar abundance properties characterized by the presence of multiple populations of low-mass stars with distinct abundance anomalies. The formation of supermassive stars (SMS) through runaway collisions in proto-GCs has been proposed to explain these phenomena. However, the understanding of SMS formation, stability, and evolution remains incomplete. In this study, we tackle key questions about SMSs and their role in the formation of multiple stellar populations in GCs. Using MESA, we successfully simulate nucleosynthesis within SMSs, revealing that they can replicate observed abundance patterns in GCs, offering a plausible explanation for the distinct anomalies.Additionally, we explore the effects of collisions and mergers by examining the inspiral of stars within SMS envelopes. Our findings indicate that the injection of energy into SMSs can lead to significant mass loss, suggesting a crucial role for collisions and mergers in the early chemical evolution of GCs.
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Lewis Prole
Title: Simulating Population III star formation
Abstract: "The first stars, known as Population III, were initially believed to be massive (>100Msun) and form in isolation. Recent advancements in simulation resolution have drastically changed this model in favour of the formation of groups of smaller stars forming within each minihalo, the mass function of which is highly unknown, yet inevitably impacts reionisation and metal enrichment in the ISM. This talk explores the environments that Population III stars form in as well as the effects of resolution, magnetic fields and stellar feedback when simulating their formation."
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Lorenz Zwick
Direct collapse of exceptionally heavy black holes in the merger-driven scenario
Major mergers of massive galaxies may provide the conditions for an extreme direct collapse event, in which the general relativistic instability is triggered at unusually large scales.
In this talk, I will go through the assumptions and requirements of the scenario, showing why it provides an interesting alternative to more traditional light seed and heavy seed models.
I will also discuss the recent and exciting JWST and Chandra observations of high redshift quasars in the context of extreme direct collapse scenarios.
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Marcelo Vergara
"Global instability by runaway collisions in nuclear stellar clusters."
"The centers of galaxies host nuclear stellar clusters, supermassive black holes, or both. The origin of this dichotomy is still a mystery. Nuclear stellar clusters are the densest stellar systems in the Universe, so they are ideal places for runaway collisions to occur. Previous studies have proposed the possible existence of a critical mass scale in such clusters, for which the occurrence of collisions becomes very frequent and leads to the formation of a very massive star, which eventually forms a black hole. While it is difficult to probe this scenario with simulations directly, we here aim for a proof of concept using toy models where the occurrence of such a transition is shown based on simplified compact systems, where the typical evolution timescales will be faster compared to the real Universe. Indeed, our simulations confirm that such a transition takes place and that up to 50% of the cluster mass can go into the formation of a central massive object for clusters that are above the critical mass scale. Our results thus support the proposed new scenario based on idealized simulations. A preliminary analysis of observed nuclear star clusters shows similar trends related to the critical mass as in our simulations."
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Masaki Kiyuna
The role of the cold accretion in the supermassive star formation
In atomic cooling halos (ACHs), which are promising sites for the formation of supermassive stars (SMSs), a phenomenon called 'cold accretion' — the direct inflow of gas from large-scale structural filaments into the halo centers — has been reported in some cosmological simulations (e.g., Wise & Abel 2007; Greif et al. 2008). Inayoshi & Omukai (2012) proposed that the effects of shock heating due to this cold accretion cause the SMS formation. However, there have been conflicting simulation results in which cold accretion has not occurred in ACHs (Fernandez et al. 2014), and its general presence and role in SMS formation have not been thoroughly investigated.
We have used cosmological hydrodynamic simulations to demonstrate the emergence of cold accretion in ACHs. With a semi-analytic model (e.g., Birnboim & Dekel 2003), we coherently interpret the discrepancies among our results and previous simulations as the differences in their observed periods. Our simulations also indicate the cold accretion provides dense hot gas clouds with ~10^4 M_\odot, which is available for the SMS formation (Kiyuna et al. 2023).
To reveal further realistic evolution after the first appearance of cold accretion, we update our simulations to include radiative feedback from newly born stars within ACHs, which was ignored in our previous simulations. We show that such stellar radiative feedback increases the amount of hot (T~10^4 K) gas near the halo centre by destroying H_2 molecules and H^- ions. The resulting situation is favourable for SMS formation (Chiaki et al. 2023). Our latest simulations show that cold accretion does indeed induce SMS formation, and even sequential SMS formation within the same halos. In this talk I will report these results and discuss the role of cold accretion in SMS formation.
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Simon Glover
Title: The IMF of Population III stars
Abstract:
Despite decades of work, major uncertainties still remain concerning the shape of the Pop III initial mass function (IMF). In this talk, I will review what we currently know about the processes shaping the Pop III IMF and highlight the main difficulties that need to be addressed in order to make progress in pinning down its form.
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Sophie Tsiatsiou
Fast-rotating massive Population III stars explain extreme nitrogen-emitters in high-redshift galaxies
Abstarct:
In this talk, I will present a comprehensive analysis of the chemical compositions found in galaxies at high redshifts, focusing specifically on nitrogen-enhanced galaxies GN-z11 and CEERS-1019. Through the utilization of massive stellar models covering a range of initial masses from 9 to 120 Msol, and various metallicities, we aim to deduce the chemical abundances of stellar ejecta for a few light elements (H, He, C, N, O, Ne). This study provides valuable insights into the chemical processes and elemental synthesis within the early universe.
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Stefania Salvadori
Unveiling the mass distribution of the first stars
The initial mass function (IMF) of the first (Pop III) stars is almost completely unknown but it controls the injection of energy, photons, and newly created heavy elements into the primordial Universe. In the Local Group, we are facing the unique opportunity to indirectly study the Pop III IMF by observing the chemical fingerprints left by first stars in their ancient and metal-poor stellar descendants and by interpreting these findings with cosmological models and simulations. In this talk, I will present the most recent observational and theoretical findings from Near-field cosmology. I will discuss how the minimum, maximum, and characteristic mass of the first stars can be limited and I will show that there is another unknown that should be considered in this game: the energy distribution of the first supernovae. Finally, I will discuss the recent discovery of a unique halo star likely imprinted by a massive primordial Pair Instability Supernova and discuss the implications of this key finding for the shape of the PopIII IMF.
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Muhammad Latif
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Volker Bromm
Formation of Supermassive Objects in the Early Universe
Recent observations with the JWST have indicated that surprisingly massive galaxies were able to form already very early in cosmic history. Similarly, we now have empirical evidence that supermassive black holes were already in place in a subset of the first galaxies. Given the short timescale available for their formation, we have a challenge at our hands to identify viable formation channels for the first massive galaxies and black holes. I will discuss possible formation pathways, including the roles played by massive and supermassive stars, together with observational probes to distinguish between different models.
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Daniel Schaerer
Exotic emission line galaxies at high-redshift: first evidence for
supermassive stars ?
I will summarize recent discoveries of "exotic" emission line galaxies
with JWST and from other data, whose spectra reveal very peculiar
abundances in their ISM, very high densities and other peculiar
properties. I will present evidence showing that these "N-emitters"
could be the sites of proto-globular clusters, and signposts of
supermassive stars in the early Universe.
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Rui Marques Coelho Chaves
