What are the main sequence stars
Pro Research Analysisby 
Searched over 200M research papers
Main Sequence Stars: Characteristics and Evolution
Introduction to Main Sequence Stars
Main sequence stars are the most numerous class of stars in the universe, representing a significant phase in stellar evolution. These stars are characterized by the fusion of hydrogen into helium in their cores, which provides the energy that makes them shine. The main sequence phase is a stable period in a star's life cycle, lasting for millions to billions of years, depending on the star's mass .
Spectroscopic Evolution of Massive Main Sequence Stars
The evolution of massive stars on the main sequence is influenced by several parameters, including initial mass and stellar winds. Spectroscopic studies have shown that the earliest O-type stars (O2-3.5) appear only in stars with initial masses above approximately 50 solar masses (M☉). As the mass increases, a larger portion of the main sequence is spent in luminosity class III, and supergiants can appear before the end of core-hydrogen burning in stars above 50 M☉. This indicates that the distribution of luminosity classes in the Hertzsprung-Russell (HR) diagram is not a straightforward diagnostic of the main sequence length for stars above 15 M☉ .
Star-Forming Main Sequence and Molecular Gas Main Sequence
The star-forming main sequence (SFMS) describes the relationship between the star formation rate (SFR) and stellar mass in galaxies. Studies using the ALMaQUEST survey have shown that the SFR surface density, stellar mass surface density, and H2 mass surface density are strongly correlated, forming a 3D linear relation. This suggests that the local gas mass traces the gravitational potential set by the local stellar mass or that both quantities follow the underlying total mass distributions. The resolved SFMS is considered the least physically fundamental, being a consequence of the Schmidt-Kennicutt (SK) and molecular gas main sequence (MGMS) relations .
Ultrashort Period Main Sequence Binary Stars
Main sequence binary stars with ultrashort periods (less than 0.2 days) are rare and not well-constrained. Recent studies have identified several new candidates, including M dwarf systems, through photometric and spectroscopic analysis. These discoveries help to better understand the lower tail of the period distribution of main sequence binaries and provide insights into their formation and evolution .
Pre-Main Sequence to Main Sequence Transition
Pre-main sequence (PMS) stars evolve into main sequence stars over time. Identifying stars in the transition phase from PMS to main sequence is crucial for understanding stellar evolution. Recent studies have identified transition phase candidates by analyzing their infrared excess and location in the optical color-magnitude diagram. These candidates exhibit characteristics intermediate between classical Be stars and Herbig Ae/Be stars, indicating their evolutionary status .
Main Sequence Stars in Star Clusters
Observations of young star clusters, such as the Upper Scorpius subgroup, have identified numerous pre-main sequence stars. These stars show a range of ages and lithium abundances, suggesting a spread of ages within the cluster. The presence of circumstellar disks in some of these stars indicates ongoing planet formation processes .
Conclusion
Main sequence stars are a fundamental component of the universe, representing a stable phase in stellar evolution. Studies of their spectroscopic properties, binary systems, and transition phases provide valuable insights into their formation, evolution, and the physical processes at play. Understanding main sequence stars is crucial for broader astrophysical research, including galaxy evolution and planet formation.
Sources and full results
Most relevant research papers on this topic