1/11/2024 0 Comments A type main sequence starStars emit a constant stream of particles known as the stellar wind. Additional phenomena include flares (bursts of light emission), prominences (large plasma and magnetic structures extending from the surface), and coronal mass ejections (ejection of stellar mass). In the photosphere, granules (convection cells of plasma), faculae (bright valleys between granules), and starspots (dark or bright spots) can be observed, while spicules (short-lived vertical jets of plasma) and plages (bright regions analogous to faculae) may be found in the chromosphere. Cooler stars possessing deep surface convection zones generally have complex and dynamic fields, resulting in various phenomena within the stellar atmosphere. Hotter stars with thin or nonexistent surface convection zones usually possess simple, stable, and dipolar fields. Additionally, cooler stars containing sufficiently deep surface convection zones have two additional layers of atmosphere: the chromosphere and the corona.ĭynamics Two main types of stellar magnetic fields play a dominant role in the dynamics of a star. Once energy produced at the core reaches the photosphere, the layer where the star becomes transparent and generally regarded as the lowest layer of the stellar atmosphere, it is finally emitted as radiation. This means, among other things, that nearly all hydrogen present within the star can enter the core and become fused over its lifetime. For example, main sequence stars less massive than roughly 7E29 kg (0.35 solar masses) are fully convective. The placement and thickness of both zones differ depending on stellar mass and the current stage in stellar evolution, and affects the dynamics of the star. This manifests as the radiation zone, where energy is transported via radiation and conduction, and the convection zone, where energy is transported via convection. In more massive stars, the core may continue fusing helium and heavier elements up to iron.Įnergy produced by fusion at the center of the star is transported to the surface via two methods: radiation and convection. Helium ash builds up within this region as the star ages, eventually causing it to become nearly hydrogen-free by the end of the main sequence phase. In main sequence stars, this is the region where hydrogen fusion happens by either the proton-proton chain, which dominates in less massive stars, or the carbon-nitrogen-oxygen (CNO) cycle, which dominates in more massive stars. Structure and dynamics Structure At the center of a star lies the core, where temperature and pressure are the greatest. The majority of stars are composed mostly of hydrogen and helium, the two most abundant elements in the universe, although there are exceptions, such as Wolf-Rayet stars or white dwarfs. Stars are celestial bodies which are sufficiently massive to naturally achieve a significant rate of nuclear fusion of hydrogen to helium in their interior at some point in their lives. Most stars in the universe today are red dwarfs: cold, dim, low mass, and extremely long-lived stars.
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