What is the main sequence of stars
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Understanding the Main Sequence of Stars
Introduction to the Main Sequence
The main sequence is a continuous and distinctive band of stars that appears on plots of stellar color versus brightness. These plots, known as Hertzsprung-Russell (HR) diagrams, are fundamental tools in the study of stellar evolution. Stars on the main sequence are in a stable phase of their lifecycle, where they are fusing hydrogen into helium in their cores.
Spectroscopic Evolution of Massive Stars on the Main Sequence
Massive stars exhibit a range of spectral types and luminosity classes as they evolve along the main sequence. The earliest O-type stars, which are extremely hot and luminous, appear only above a certain mass threshold (~50 solar masses)1. As stars increase in mass, a larger portion of their main sequence lifetime is spent as giants rather than dwarfs. For instance, stars above 50 solar masses can become supergiants before they exhaust their core hydrogen1. This spectroscopic evolution is crucial for understanding the lifecycle of massive stars and their impact on galactic environments.
Sub-Galactic and Nuclear Main Sequences
The concept of the main sequence extends beyond individual stars to entire galaxies. Within star-forming galaxies, there exists a sub-galactic main sequence (SGMS) that relates the star formation rate surface density to the stellar mass density on kiloparsec scales2. This relationship holds true even within the nuclei of galaxies, indicating that the most active star-forming regions are often found in the central areas. The SGMS is similar to the global main sequence but provides more detailed insights into the spatial distribution of star formation within galaxies.
Molecular Gas Main Sequence and Star Formation
The star-forming main sequence (SFMS) is a well-established relation between the star formation rate and stellar mass of galaxies. Recent studies have identified a molecular gas main sequence (MGMS), which links the molecular gas mass surface density to the stellar mass surface density3. This relationship suggests that the local gas mass is closely tied to the gravitational potential set by the local stellar mass. The SFMS is thus a consequence of the interplay between the MGMS and the Schmidt-Kennicutt relation, which connects star formation rate to gas mass3.
Convection in Main Sequence Stars
Convection plays a significant role in the structure and evolution of main sequence stars. It occurs in various forms, from thin shells to nearly spherical cores, and can be either efficient or inefficient depending on the star's mass and evolutionary stage5. Understanding these convection processes is essential for accurate stellar modeling and for predicting the behavior of stars throughout their main sequence lifetimes.
Star Formation and Quenching
The main sequence of star-forming galaxies is a critical framework for studying galaxy evolution. Galaxies that lie above the main sequence exhibit enhanced star formation, often concentrated in their central regions, while those below the main sequence show reduced star formation, potentially due to quenching processes6. Active galactic nuclei (AGN) are thought to play a key role in quenching star formation, leading to the transition of galaxies from the "blue cloud" of active star formation to the "red-and-dead" phase7.
Conclusion
The main sequence is a fundamental concept in both stellar and galactic astronomy. It describes the stable phase of hydrogen burning in stars and provides a framework for understanding the star formation and evolution of galaxies. From the spectroscopic evolution of massive stars to the spatially resolved star formation in galaxies, the main sequence remains a cornerstone of astrophysical research. Understanding the various aspects of the main sequence helps astronomers to piece together the complex processes that govern the lifecycle of stars and the evolution of galaxies.
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Most relevant research papers on this topic
Spectroscopic evolution of massive stars on the main sequence
The evolution of massive stars is influenced by parameters like mass, spectral type, and wind densities, with a lower mass limit for dwarf stars and a higher mass limit for supergiants.
The sub-galactic and nuclear main sequences for local star-forming galaxies
The sub-galactic main sequence (SGMS) reveals that star formation rates and stellar masses peak in the nucleus of star-forming galaxies, with circumnuclear clusters being the most active and massive regions.
The ALMaQUEST Survey: The Molecular Gas Main Sequence and the Origin of the Star-forming Main Sequence
The molecular gas main sequence (MGMS) may be the least physically fundamental factor in the star-forming main sequence, with the resolved SFMS being the result of the combination of the Schmidt-Kennicutt and MGMS relations.
Reconciling mass functions with the star-forming main sequence via mergers
Combining star formation and merging can reconcile galaxy evolution, allowing for a model in which hierarchical merging is disconnected from environmentally independent star formation.
An Atlas of Convection in Main-sequence Stars
This paper explores the diverse nature of convection in main-sequence stars, revealing its diverse conditions, efficiency, and rotational constraints, providing a guide for future theoretical and observational investigations.
Star formation is boosted (and quenched) from the inside-out: radial star formation profiles from MaNGA
Star formation in galaxies is boosted from the inside-out, with the greatest enhancement occurring at small radii, and may lead to galactic quenching from the inside-out.
Highly CitedQuenching star formation: insights from the local main sequence
Star formation quenching by active galactic nuclei (AGN) plays a key role in the evolutionary pathway of galaxies, from blue cloud to red-and-dead galaxies.
AN OBJECTIVE DEFINITION FOR THE MAIN SEQUENCE OF STAR-FORMING GALAXIES
The main sequence of star-forming galaxies can be defined objectively as the ridge line of the peak in a 3D SFR-mass-number plot, improving inter-comparison and understanding of galaxy evolution.
Highly CitedIdentification of emission-line stars in transition phase from pre-main sequence to main sequence
This study identified 98 'transition phase' stars, which are evolving from pre-main sequence to main sequence, with ages between 0.1-5 Myr and masses between 2-100.5 M.
SPATIALLY RESOLVED STAR FORMATION MAIN SEQUENCE OF GALAXIES IN THE CALIFA SURVEY
The main sequence of galaxies is a tightly related relation between star formation rate and total stellar mass, with variations in slope and old stellar population dominance.
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