arXiv subjects

Ke-Jung Chen

Publications and source records attributed to Ke-Jung Chen.

At least 19 recordsLinked to original sources

arXiv2026

Observable Signatures of Supernova Shock Breakout in Confined Circumstellar Medium

Supernova shock breakout encodes rich information about stellar explosions, including the properties of the progenitor, the explosion mechanism, and the circumstellar environment. We present the first two-dimensional multigroup radiation-hydrodynamic simulations of shock breakout from Red Supergiant (RSG) progenitor stars embedded in confined circumstellar medium (CSM) produced shortly before core collapse. Our simulations reveal that radiation escaping ahead of the shock forms a radiative precursor that pre-accelerates the CSM and induces strong hydrodynamic mixing. This mixing substantially modifies the structure and evolution of the breakout photosphere and, consequently, the emergent radiation. The resulting bolometric light curves reach peak luminosities of $1.43$-$3.15 \times 10^{44}\ \mathrm{erg\ s^{-1}}$ with duration of $4.1\text{--}35.4$~hr, with these signatures controlled by the CSM mass and the confined radius. Our multiwavelength calculations further reveal a pronounced extreme-ultraviolet emission, where ionizing photons of energies ${\ge}54.4$~eV can sustain flash-ionized He-II and power strong emission from its recombination line of $λ4686$ angstrom. Furthermore, we identify diagnostic signatures of shock breakout with dense CSM and assess their detectability with Einstein Probe and ULTRASAT. Our models and predictions provide promising diagnostics of shock breakout in CSM that may be detectable by current and forthcoming high-cadence ultraviolet and X-ray space telescopes.

astro-ph.HE↗

arXiv2026

Formation of Heavy Seed Black Holes and Little Red Dots-like Compact Clusters in Metal-enriched Star-forming Regions

The origin of supermassive black holes (SMBHs) in the early Universe remains uncertain. While the classical direct-collapse scenario requires pristine gas exposed to intense Lyman-Werner (LW) radiation, recent JWST observations suggest that early growing BHs may reside in compact, metal-enriched environments. We investigate early BH formation using a cosmological radiation-hydrodynamic simulation that self-consistently follows the formation and evolution of rapidly accreting supermassive stars (SMSs). We find that intense LW radiation develops in clustered star-forming regions; by the time the first heavy seed forms, the mass-weighted internal intensity has reached $J_{21}\sim1000$. Most seeds form in weakly metal-enriched gas with [Z/H]$\sim-3$ to $-2$, because the strongest LW fields occur in regions already enriched by previous stellar feedback. All halos above $10^9M_\odot$ in our zoom-in region host a BH more massive than $10^5M_\odot$. We construct stellar spectra using MIST/PHOENIX libraries for normal stars and $6000~\mathrm{K}$ blackbody spectra for bloated SMSs. Five of eight massive clusters with stellar masses larger than $10^6~M_\odot$ exhibit intrinsically V-shaped spectra similar to those of Little Red Dots (LRDs). In the most prominent cases, luminous SMSs dominate the red optical emission, although Balmer breaks in normal stellar populations also contribute. We also identify off-center LRD-like systems in our simulation resembling those recently reported in strongly lensed observations. Our results suggest that heavy-seed formation, compact-cluster formation, and LRD-like continuum emission are linked outcomes of clustered, weakly metal-enriched, strongly irradiated environments.

astro-ph.GA↗

arXiv2026

Supernova feedback in porous photoionized Giant Molecular Clouds

We present a new suite of numerical simulations of Type II supernovae (SNe) detonating in Giant Molecular Clouds with a variety of density structures shaped by photoionization feedback. Ionizing radiation sculpts cavities and channels that guide SN energy to emerge from the cloud as shock-driven blowouts, rather than as a coherent spherically expanding shell as assumed in most sub-grid SN models adopted in galaxy or cosmological simulations. We investigate how such outflows differ to the 1-D descriptions, and whether or not the perturbations induced by the blowouts are sensitive to the host cloud's structure. A channelling parameter $P_\mathrm{chnl}$ is introduced to characterise the cloud's porosity and boundness using the morphology of the ionized channels. Our results reveal that the outflow velocities, whilst consistently higher than that of the spherical blasts, are in fact rather independent of the porosity of its local environment. The total kinetic energy and momentum deposited also appear similar across all runs. What is most sensitive to $P_\mathrm{chnl}$ is the mass of the materials carried in the outflows and their migration distances. It implies that SNe exploding in compact clouds with distinctive channel structures may have more confined metal injection radii and shortened turbulent driving scales, which consequently lead to a clumpier interstellar medium with higher density and metallicity fluctuations. We argue that molecular cloud structures play an equally important role to SN rates and energy budgets in stellar feedback sub-grid modelling.

astro-ph.GA↗

arXiv2026

Interacting Binary Stars as Progenitors for Interacting Supernovae

Dense, compact circumstellar media (CSM) are required to power strongly interacting supernovae, yet their physical origin remains uncertain. We present a systematic study of binary stellar evolution models computed with MESA, demonstrating that Case C mass transfer, initiated after core helium ignition, can naturally produces the dense, nearby CSM inferred in interacting events. Across a grid of binary models, we find that donors of 10--20 solar masses in binaries with separations of approximately 1000--2700 solar radius undergo late-stage Roche-lobe overflow within ~10^3 yr prior to core collapse, ejecting ~0.01--0.2 solar masses and forming CSM extending to ~10^16--10^18 cm. Our results suggest that the Case C mass transfer may account for ~13% of all core-collapse supernova (CCSN) progenitors, rather than representing a rare channel. A subset of these Case C binaries produces CSM properties that are quantitatively in agreement with those inferred for interacting supernovae such as SN 2014C. In contrast to earlier binary interactions or single-star mass loss, Case C transfer operates at the right time and scale to shape the immediate pre-supernova environment without requiring ad hoc eruptive mechanisms. Our results identify late-stage binary interaction as a robust and physically motivated channel for producing the dense CSM that powers interacting supernovae.

astro-ph.HE↗

arXiv2026

Turbulence in Primordial Dark Matter Halos and Its Impact on the First Star Formation

We present high-resolution simulations of the first star-forming clouds in 15 minihalos with masses ranging from $\sim 10^5$ to $10^7\ \text{M}_{\odot}$ at redshifts $z \sim 17-20$, using the GIZMO code. Our simulations incorporate detailed primordial gas physics and adopt initial conditions from the state-of-the-art TNG cosmological simulations. To achieve the required resolution, we apply a particle-splitting technique that increases the resolution of the original TNG data by a factor of $\sim 10^5$, reaching gas and dark matter particle masses of $0.2\ \text{M}_{\odot}$ and $80\ \text{M}_{\odot}$, respectively. This enables us to resolve gas accretion during the early assembly of minihalos and to capture the emergence of strong turbulent flows. We find that turbulence, driven by gas infall into the dark matter potential wells, is predominantly supersonic, with characteristic Mach numbers ranging from $1.8$ to $4.2$, increasing with halo mass. The supersonic turbulence effectively fragments the central gas cloud into multiple clumps. Some of dense clump masses range from $2.6~\text{M}_{\odot}$ to $66.5~\text{M}_{\odot}$ exceeding their corresponding Jeans masses and soon collapsing to form the first stars. Our results suggest that supersonic turbulence is a common feature in minihalos and plays a key role in generating clumpy star-forming clouds, with important implications for the initial mass function of the first stars.

astro-ph.GA↗

arXiv2026

Why Do Stars Turn Red? I. Post-Main-Sequence Expansion Mechanism

In this series of papers, we address the long-standing question of why post-main-sequence stars expand into red giants (RGs) or red supergiants (RSGs). This paper aims to identify the key physical mechanism that drives stellar evolution toward the RG/RSG phase. Using the Modules for Experiments in Stellar Astrophysics (MESA), we perform controlled numerical experiments by systematically varying stellar parameters in evolutionary models, and compare those that successfully evolve into RG/RSGs and those that do not. We show that envelope expansion toward the RG/RSG phase cannot be explained by energy absorption. Instead, it is governed by a refined form of the "mirror principle," in which the stellar envelope responds oppositely to its inner boundary, defined by the outer edge of the hydrogen-burning shell, rather than directly to the helium core. This behavior arises naturally from hydrostatic equilibrium, as the burning shell establishes a moving, nearly constant-pressure inner boundary for the envelope. We identify two evolutionary pathways toward the RG/RSG phase that both follow this refined mirror principle: (1) direct envelope expansion during helium-core contraction, and (2) continued expansion after contraction ceases, driven by a decline in nuclear energy generation rate. The final approach to the RG/RSG phase is marked by a structural transition in the envelope, characterized by mass redistribution and the development of an extended convective region. We present a unified physical framework for envelope expansion toward the RG/RSG phase, based on the refined mirror principle and the final structural transition, and outline an evolutionary roadmap leading to the RG/RSG phase.

astro-ph.SR↗

arXiv2026

Why Do Stars Turn Red? II. Steady-State Envelope Solutions

The physical origin of red giants (RGs) and red supergiants (RSGs) remains a fundamental question in stellar astrophysics. In Paper II of this series, we investigate the physical mechanisms governing envelope expansion toward the RG/RSG phase by systematically exploring the physically realizable configurations of stellar envelopes. We construct steady-state stellar envelope models by solving the time-independent stellar structure equations while neglecting the core. The inner boundary is defined by a fixed pressure condition motivated by MESA stellar evolution models presented in Paper I. Our models show three key features of envelope expansion toward the RG/RSG phase. (1) The refined mirror principle identified in Paper I is recovered: the post-main-sequence stellar radius varies inversely with the radius of the envelope's inner boundary, arising purely from hydrostatic equilibrium. (2) We identify an upper limit to envelope expansion corresponding to an effective temperature of $\sim 4000,{\rm K}$, characteristic of RG/RSG stars and consistent with the Hayashi limit. This temperature limit is regulated by H$^{-}$ opacity, whose sharp decline at low temperatures flattens the surface temperature gradient and drives a structural transition. (3) The yellow regime of intermediate radius corresponds to an instability zone, in which small displacements of the hydrogen-burning shell produce large variations in stellar radius, naturally accounting for the bifurcation of giants and supergiants into blue and red branches instead of remaining in the yellow regime.

astro-ph.SR↗

arXiv2026

Multi-wavelength Signatures of Supernova Shock Breakout from Red Supergiants in Two Dimensions

We present new two-dimensional radiation hydrodynamic simulations of supernova shock breakout from red supergiants using the $\texttt{CASTRO}$ code. Our progenitors are 20 and 25 M$_{\odot}$ solar-metallicity stars evolved from the zero-age main sequence with $\texttt{MESA}$ and exploded in one dimension using $\texttt{FLASH}$. We consider a range of circumstellar media (CSM) produced by stellar winds to investigate how pre-explosion mass-loss affects shock breakout. The multigroup flux-limited diffusion scheme in $\texttt{CASTRO}$ captures the interaction between the explosion shock, its radiation precursor, and the surrounding CSM. We find that strong radiation precursors, generated by radiation leakage behind the shock, can drive fluid instabilities and move the effective photosphere outward before the shock reaches the stellar surface. The resulting breakout emissions reach peak luminosities of ${\sim}10^{44}$ erg s$^{-1}$ with full-width half-maximum durations of 1-3 hr, , fainter and longer than previous 1D models. The light-curve colors gradually evolve from blue to red after the peak. The 25 M$_{\odot}$ model with explosion energy $E \sim 1.69\times10^{51}$ erg produces ${\sim}$10-30\% higher maximum luminosity than the 20 M$_{\odot}$ model with $E \sim 1.09\times10^{51}$ erg. The dense CSM further extends the breakout rise time by increasing the photon diffusion. These results provide new constraints on red supergiant atmospheres and mass-loss histories prior to core collapse.

astro-ph.HE↗

arXiv2026

Critical Metallicity of Cool Supergiant Formation. II. Physical Origin

This study investigates the physical origin of the critical metallicity required for the formation of cool supergiants, as revealed by stellar evolution models. Using grids of stellar models, we show that the terminal-age main-sequence (TAMS) radius, $R_{\rm TAMS}$, defines a threshold that determines whether a star of a given mass can evolve into the red supergiant (RSG) phase. Metallicity influences the supergiant outcome because it modifies $R_{\rm TAMS}$ through its effects on opacity and nuclear energy generation, as demonstrated by our stellar models and dimensional analysis based on homology relations. The value of $R_{\rm TAMS}$ sets the initial radius for post-main-sequence expansion and therefore controls the envelope radius reached at subsequent core-evolution stages. Higher-metallicity stars develop larger $R_{\rm TAMS}$ and rapidly expand into the stable RSG regime during core helium burning. In contrast, lower-metallicity stars have smaller $R_{\rm TAMS}$ and advance to more evolved core helium or carbon-burning stages while retaining compact envelopes, thereby preventing expansion into the RSG regime during core helium burning. Our results explain the origin of the critical metallicity and offer insight into the evolution of metal-poor massive stars in the early universe.

astro-ph.SR↗

arXiv2025

Formation of Supersonic Turbulence in the Primordial Star-forming Cloud

We present new simulations of the formation and evolution of the first star-forming cloud within a massive minihalo of mass of $1.05 \times 10^7\, M_{\odot}$, carried out using the GIZMO code with detailed modeling of primordial gas cooling and chemistry. Unlike previous studies that simulated the formation of the first stars within a smaller cosmological boxsize of $\sim 1-2$ Mpc, our work adopts initial conditions from the large-scale cosmological simulations, IllustrisTNG spanning $\sim 50$ Mpc to study the formation of primordial clouds that give birth to the first stars. We increase the original resolution of IllustrisTNG by a factor of $\sim10^5$ using a particle-splitting technique, achieving an extremely high resolution that allows us to resolve turbulence driven by gravitational collapse during early structure formation. We find that strong supersonic turbulence with a characteristic Mach number of $\sim 5.2$ naturally develops within the collapsing halo. This turbulence efficiently stirs the gas, promoting fragmentation of the star-forming cloud into multiple dense clumps. Among them, we identify a gravitationally bound core with a mass of $8.07\,M_{\odot}$ and a size of $0.03$ pc, which exceeds its local Jeans mass and is on the verge of collapsing into a star. Our results indicate that supersonic turbulence may be common in primordial halos and can play a crucial role in cloud-scale fragmentation, potentially lowering the characteristic mass scale of the first stars.

astro-ph.GA↗

arXiv2025

Inferring Dense Confined Circumstellar Medium around Supernova Progenitors via Long-term Hydrodynamical Evolution

Circumstellar interaction of supernova (SN) ejecta is an essential process in its evolution and observations of SNe have found the signature of circumstellar interaction both in the early and late evolutionary phase of SNe. In this Letter, we show that if the SN forward shock plunges into tenuous stellar wind from dense circumstellar medium (CSM) in the vicinity of the progenitor (i.e., confined CSM), the subsequent time evolutions of the SN-CSM interaction system deviates from the prediction of self-similar solution. In this case, after all of the confined CSM is swept up by the SN forward shock (roughly $10$ days after the explosion), the propagation of the shocked shell will be driven by the freely expanding ram pressure of the confined CSM component, instead of the SN ejecta. Meanwhile, the forward shock decelerates faster than the prediction of thin-shell approximation once the confined CSM component reaches homologous expansion. This lasts until the reverse shock in the confined CSM component reaches the head of the SN ejecta, leading to the restoration of the system into the evolutionary model without confined CSM, where the SN ejecta drives the expansion of the system. We also show that this peculiar evolution will be reflected in observational signatures originating from SN-CSM interaction, taking rapid decline and rebrightening of radio emission as examples. Our results shed light on the importance of taking into account the effect of initial SN-CSM interaction even when we focus on observational properties of SNe a few years after the explosion.

astro-ph.HE↗

arXiv2025

Coevolution of Dwarf Galaxies and Their Circumgalactic Medium Across Cosmic Time

Dwarf galaxies are thought of as the building blocks of large galaxies such as our Milky Way. This paper presents new high-resolution hydrodynamical simulations of dwarf galaxies and their intergalactic medium with the \texttt{GIZMO} code. Our simulations consider the key physical processes of galaxy evolution, such as gas cooling, chemistry, and stellar and black hole feedback. Unlike the previous work, the initial conditions of our simulations taking the dwarf galaxies of $2-5 \times 10^{10} \, M_\odot$ from the realistic cosmology simulations, \texttt{IllustrisTNG}. We further increase the original resolution of \texttt{IllustrisTNG} by a factor of $\sim 100$ via a particle splitting scheme. Our results show that the evolution of complex multiphase CGM and its metal content is sensitive to the redshift of dwarf galaxies. The accretion of CGM into dwarf galaxies plays a key role in providing $20 \% - 50 \%$ of the star-forming gas and replenishing $40 \% - 70 \%$ of the total mass in the galactic disk. Furthermore, the accretion history of supermassive black holes in the centers of high-$z$ dwarf galaxies shows episodic patterns with high-accreting states close to $\sim 10 \%$ of the Eddington mass accretion rate, implying the rapid growth of supermassive black holes in the early universe, which may be revealed by the coming observations from the James Webb Space Telescope (JWST).

astro-ph.GA↗

arXiv2025

Cosmic Ly$α$ Emission from Diffuse Gas

The Ly$α$ emission has emerged as a powerful tool for probing diffuse gas within the large-scale structure of the universe. In this paper, we investigate cosmic Ly$α$ emission by post-processing cosmological simulations from \texttt{IllustrisTNG} and \texttt{THESAN} project. Specifically, we calculate the Ly$α$ emission from galaxies, circum-galactic medium (CGM) and inter-galactic medium (IGM) across various redshifts. Our results show that IGM alone is significantly under the current observational upper limits. Meanwhile, CGM overshoots the observed galaxy contribution at $z \lesssim 0.5$ indicating that either the escape fraction for the inner CGM is less than unity or the current photoionization equilibrium treatment with an approximate self-shielding prescription is less accurate. The galaxy component also overshoots at low redshift, indicating that the escape fraction has strong evolution caused by an evolving halo mass function and dust growth distribution, that agrees with observationally inferred escape fractions. Furthermore, our findings suggest that the Ly$α$ emission from diffuse gas (CGM+IGM) peaked at $z \sim 4$ and diminishes toward lower redshift. The Ly$α$ emission from diffuse gas mainly originates through the collisional excitation of hot plasma. By comparing models with observation, our predicted Ly$α$ emission from diffuse gas remains $\sim 6$ times fainter than the observed cosmic Ly$α$ emission at $z=1-3$. However, future large telescopes may hold great promise to detect Ly$α$ emission from diffuse gas toward $z>3$.

astro-ph.CO↗

arXiv2025

Origins of Supermassive Black Holes in Galactic Centers

Direct imaging of black hole shadow halos has firmly confirmed the existence of supermassive black holes (SMBHs), with millions of solar masses, residing at the centers of the Milky Way and M87 galaxies. These groundbreaking discoveries represent a monumental success of Einstein's theory of general relativity and have revealed the hidden "monsters" lurking at the centers of galaxies. Moreover, observations of active galactic nuclei (AGNs) indicate that SMBHs with billions of solar masses were already in place within the first billion years after the Big Bang. However, the origins of these SMBHs, as well as their co-evolution with host galaxies, remain poorly understood. This review focuses on the origin of SMBHs, particularly on the formation of their seed black holes. We also highlight several outstanding challenges in modeling seed formation and discuss possible observational signatures. These signatures may be testable with current and future facilities, including the James Webb Space Telescope (JWST) and the upcoming gravitational wave observatory, the Laser Interferometer Space Antenna (LISA).

astro-ph.CO↗

arXiv2024

Multidimensional Radiation Hydrodynamics Simulations of Supernova 1987A Shock Breakout

Shock breakout is the first electromagnetic signal from supernovae (SNe), which contains important information on the explosion energy and the size and chemical composition of the progenitor star. This paper presents the first two-dimensional (2D) multi-wavelength radiation hydrodynamics simulations of SN 1987A shock breakout by using the $\texttt{CASTRO}$ code with the opacity table, $\texttt{OPAL}$, considering eight photon groups from infrared to X-ray. To investigate the impact of the pre-supernova environment of SN 1987A, we consider three possible circumstellar medium (CSM) environments: a steady wind, an eruptive mass loss, and the existence of a companion star. In sum, the resulting breakout light curve has an hour duration and its peak luminosity of $\sim 4\times 10^{46}\,\rm{erg\,s^{-1}}$ then following a decay rate of $\sim 3.5\,\rm{mag\,hour^{-1}}$ in X-ray. The dominant band transits to UV around 3 hours after the initial breakout, and its luminosity has a decay rate of $\sim 1.5\,\rm{mag\,hour^{-1}}$ that agrees well with the observed shock breakout tail. The detailed features of breakout emission are sensitive to the pre-explosion environment. Furthermore, our 2D simulations demonstrate the importance of multidimensional mixing and its impacts on shock dynamics and radiation emission. The mixing emerging from the shock breakout may lead to a global asymmetry of SN ejecta and affect its later supernova remnant formation.

astro-ph.HE↗

arXiv2024

Modeling the Progenitor Stars of Observed IIP Supernovae

Type IIP supernovae (SNe IIP) are thought to originate from the explosion of massive stars > 10 Msun. Their luminosity is primarily powered by the explosion energy and the radioactive decay energy of 56Co, with the photosphere location regulated by hydrogen recombination. However, the physical connections between SNe IIP and their progenitor stars remain unclear. This paper presents a comprehensive study of SNe IIP and their progenitor stars by using the one-dimensional stellar evolution code, MESA. Our model grids consider the effects of stellar metallicity, mass, and rotation in the evolution of massive stars, as well as explosion energy and 56Ni production in modeling supernovae. To elucidate the observed SNe IIP and their origins, we compare their light curves (LCs) with our models. Furthermore, we investigate the impact of stellar parameters on LCs by considering stellar mass metallicity, rotation, explosion energy, and 56Ni production. We find that more massive stars exhibit longer plateaus due to increased photon diffusion time caused by massive ejecta. Higher metallicity leads to increased opacity and mass loss of progenitor stars. Rapid rotation affects internal stellar structures, enhancing convective mixing and mass loss, potentially affecting the plateau's brightness and duration. Higher explosion energy results in brighter but shorter plateaus due to faster-moving ejecta. 56Ni mass affects late-time luminosity and plateau duration, with larger masses leading to slower declines.

astro-ph.SR↗

arXiv2024

Clumpy Structures within the Turbulent Primordial Cloud

The primordial clouds in the mini-halos hatch the first generation stars of the universe, which play a crucial role in cosmic evolution. In this paper, we investigate how the turbulence impacts the structure of primordial star-forming cloud. Previous cosmological simulations of the first star formation predicted a typical mass of around $\mathrm{ 100 \, M_\odot}$, which conflicts with recent observations of extremely metal-poor stars suggesting a lower mass scale of around $\mathrm{25 \, M_\odot}$. The discrepancy may arise from unresolved turbulence in the star-forming cloud, driven by primordial gas accretion during mini-halo formation in the previous simulation. To quantitatively examine the turbulence effect on the primordial cloud formation, we employ the adaptive mesh refinement code $\mathtt{Enzo}$ to model the gas cloud with primordial composition, including artificial-driven turbulence on the cloud scale and relevant gas physics. This artificial-driven turbulence utilizes a stochastic forcing model to mimic the unresolved turbulence inside mini-halos. Our results show that turbulence with high Mach number and compressional mode effectively fragments the cloud into several clumps, each with dense cores of $\mathrm{22.7 - 174.9 \, M_\odot}$ that undergo Jeans instability to form stars. Fragmentation caused by intense and compressive turbulence prevents the runaway collapse of the cloud. The self-bound clumps with smaller masses in turbulent primordial cloud suggest a possible pathway to decrease the theoretical mass scale of first stars, further reconciling the mass discrepancy between simulations and observations.

astro-ph.GA↗

arXiv2024

How Population III Supernovae Determined the Properties of the First Galaxies

Massive Pop III stars can die as energetic supernovae that enrich the early universe with metals and determine the properties of the first galaxies. With masses of about $10^9$ Msun at $z \gtrsim 10$, these galaxies are believed to be the ancestors of the Milky Way. This paper investigates the impact of Pop III supernova remnants (SNRs) from both Salpeter-like and top-heavy initial mass functions (IMFs) on the formation of first galaxies with high-resolution radiation-hydrodynamical simulations with the ENZO code. Our findings indicate that SNRs from a top-heavy Pop III IMF produce more metals, leading to more efficient gas cooling and earlier Pop II star formation in the first galaxies. From a few hundred to a few thousand Pop II stars can form in the central regions of these galaxies. These stars have metallicities of $10^{-3}$ to $10^{-2}$, Zsun, greater than those of extremely metal-poor (EMP) stars. Their mass function follows a power-law distribution with $dN(M_*)/dM_* \propto M_*^α$, where $M_*$ is stellar mass and $α= 2.66 - 5.83$ and is steeper for a top-heavy IMF. We thus find that EMP stars were not typical of most primitive galaxies.

astro-ph.GA↗