Where do stars come from
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The Origins of Stars: A Comprehensive Overview
Formation of the First Stars: Primordial Star Formation
The formation of the first stars, known as Population III stars, marked a significant transformation in the early Universe. These stars emerged a few hundred million years after the Big Bang, ending the cosmic dark ages. The initial conditions for primordial star formation can be inferred from the Λ cold dark matter (ΛCDM) model, which predicts the formation of minihalos with masses around 10^6 solar masses (M☉) at redshifts z ≈ 20-30. These minihalos, through molecular hydrogen cooling, led to the formation of massive stars, often in binary or small multiple systems due to fragmentation in protostellar disks1.
Dark Stars: An Alternative Early Star Formation Mechanism
Dark stars represent a unique class of early stars powered by dark matter annihilation rather than nuclear fusion. These stars, composed primarily of hydrogen and helium, could grow to supermassive sizes (up to 10^6 M☉) and remain cool with surface temperatures around 10,000 K. Dark stars might have provided the seeds for supermassive black holes observed in the Universe today5.
Star Formation in Modern Galaxies: In-Situ, Migrated, and Ex-Situ Stars
In contemporary galaxies, star formation occurs through various processes. Stars can form in-situ within the galactic center, migrate from other parts of the galaxy, or be accreted from other galaxies. In-situ and migrated stars dominate the central stellar mass, with ex-situ stars contributing significantly in more massive galaxies. These processes highlight the complex interaction history and the necessity of a cosmological context in understanding star formation3.
The Role of Molecular Clouds and Yellowballs in Star Formation
Stars form within cold, dusty molecular clouds that are invisible in visible light but can be observed in infrared. An early stage in star development, identified as "yellowballs," has been crucial in understanding star formation. These yellowballs are regions within molecular clouds where new stars are beginning to form, providing insights into the initial stages of stellar birth4.
Hydrodynamical Simulations and Star Formation Rates
Hydrodynamical simulations have been instrumental in studying star formation from the "dark ages" to the present. These simulations include factors like radiative heating, cooling, supernova feedback, and galactic winds. They show that star formation rates peaked at redshifts z ≈ 5-6 and that about 50% of stars formed by redshift z ≈ 2.14. These simulations also suggest that star formation occurs preferentially in halos of varying masses over time, contributing to our understanding of cosmic star formation history8.
Insights from Numerical Simulations
Numerical simulations have provided essential insights into the star formation process, revealing it as a highly nonuniform and runaway process. These simulations show the formation of circumstellar disks and the episodic nature of accretion driven by gravitational instabilities. They also highlight the importance of filamentary structures in star-forming clouds and the hierarchical nature of star cluster formation10.
Conclusion
The formation of stars is a complex and multifaceted process that has evolved from the early Universe to the present day. From the primordial stars that ended the cosmic dark ages to the diverse mechanisms of star formation in modern galaxies, our understanding has been significantly enhanced by theoretical models, hydrodynamical simulations, and observational data. As we continue to explore the cosmos with advanced telescopes and simulations, our knowledge of where stars come from will only deepen, revealing more about the intricate processes that govern the Universe.
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Most relevant research papers on this topic
Formation of the first stars
The first stars were predominantly massive, and understanding their formation is crucial for understanding the early universe and its transformation.
Highly CitedThe Formation of the First Star in the Universe
At most one massive metal-free star forms per pregalactic halo, with radiation feedback inhibiting star growth and preventing further star formation in the same pregalactic object.
Highly CitedThe Origin of Stars in the Inner 500 Parsecs in TNG50 Galaxies
In-situ and migrated stars dominate the central stellar mass budget in galaxies, with ex-situ stars being the oldest, metal-poor, and -enhanced population, highlighting the need for cosmological context in galaxy center formation scenarios.
Dark stars: a review
Dark stars, powered by dark matter annihilation, may have been the first phase of stellar evolution in the history of the Universe.
The big problems in star formation: The star formation rate, stellar clustering, and the initial mass function
Star formation is driven by cosmic evolution, but current theories lack a comprehensive, quantitative theory to explain star formation rate, clustering, and initial mass function.
Highly CitedThe puzzle of the CNO abundances of α Cygni variables resolved by the Ledoux criterion
The Ledoux criterion for convection significantly improves agreement with observed chemical compositions of blue supergiant stars, while maintaining agreement with pulsation periods.
The history of star formation in a lcdm universe
Our model predicts that about 50% of stars formed in halos less massive than 10 11:5 h i1 Mfl, with the UV background being dominated by stars for redshifts z > 4.
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