How does a star look like
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Understanding the Appearance of a Star
Star Image Profile: Central Core and Extended Aureole
A star's image profile is characterized by a central core, an exponential drop-off, and an extended inverse-square aureole. This profile extends from the central peak out to a radius of six degrees. The exact origin of this shape remains not well understood, but it is a consistent feature observed in star images1.
Gravitational Collapse: Redshift and Visibility
During the gravitational collapse of a star, its optical image evolves significantly. The star's surface emits radiation that follows Lambert's cosine law, and as the collapse progresses, the redshift factor remains finite. This means that the star gradually becomes invisible due to the decay of the photon flux. This phenomenon can be observed through spectral photon flux and spectral radiant flux measurements, which show a decrease in visibility over time2.
Stars in Magnetic Grand Minima: Low Activity Characteristics
Stars in a Maunder-like magnetic minimum exhibit distinct characteristics. These stars, including the Sun during its low activity phases, show reduced magnetic activity and can be identified through X-ray observations. Such stars are less active compared to their more magnetically active counterparts3.
Stellar Shape: Asteroseismology and Rotational Effects
Stars are not perfectly spherical; they are deformed by rotation and magnetic fields. Asteroseismology, which measures stellar oscillations, has provided precise measurements of stellar shapes. For instance, an A-type star with a rotation period of 100 days shows a slight flattening, with a difference in radius between the equator and the poles of about 3 km. This flattening is much less than expected, suggesting the presence of a weak magnetic field5.
Young Stars: Dusty Disks and Accretion
Young stars, such as LkHα101, are often surrounded by dusty tori. These stars form from collapsing clouds of dust and gas, which initially create a rotating disk. This disk feeds material onto the forming star until thermonuclear fusion begins. High-resolution images of such stars reveal structures like central gaps and hot inner edges in the accretion disks, shaped by the sublimation of dust grains due to direct stellar radiation6.
Star Formation: Complex Multi-Scale Processes
Star formation is a complex process involving multiple scales and physical phenomena. It begins with the collapse of molecular clouds and involves various feedback mechanisms such as radiation, winds, and supernovae. These processes are crucial for understanding the lifecycle of stars and the dynamics within star-forming regions7.
Conclusion
The appearance of a star is influenced by various factors, including its image profile, gravitational collapse, magnetic activity, rotational deformation, and the presence of surrounding dust and gas. Each of these aspects contributes to the complex and dynamic nature of stars, making them fascinating objects of study in astronomy.
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Most relevant research papers on this topic
THE PROFILE OF A STAR IMAGE
The profile of a star image has a central core, exponential drop, and extended inverse-square aureole, with its origin well understood but its shape remains unresolved.
Highly CitedHow does a collapsing star look?
A collapsing star gradually becomes invisible due to decay of photon flux, with the redshift factor remaining finite and the star becoming gradually invisible due to decay of photon flux.
Stars in magnetic grand minima: where are they and what are they like?
Stars in magnetic grand minima have low physical and magnetic activity, and can be found using new X-ray observations.
Direct evidence of star structure from nuclear magnetic resonance spectroscopy
This study provides direct evidence of star structure using nuclear magnetic resonance spectroscopy, revealing the key point of the star, the silicon atom, in polybutadiene and polyisoprene stars with up to four arms.
Shape of a slowly rotating star measured by asteroseismology
A-type star with a 100-day rotation period has a tiny flattening of its shape, suggesting a weak magnetic field and questioning the origin of the magnetic field.
A dusty torus around the luminous young star LkHα101
The inner accretion disk of LkH101 is face-on, with a central gap and hot inner edge, suggesting that the inner edge is likely determined by sublimation of dust grains by direct stellar radiation.
Highly CitedPhysical Processes in Star Formation
Star formation is a complex multi-scale phenomenon involving thermal, chemical, turbulence, magnetic fields, gravitational forces, and stellar feedback mechanisms.
Zooming in on Individual Star Formation: Low- and High-Mass Stars
Recent technological and computing advances have transformed our understanding of star formation, improving our understanding of both high-mass and low-mass star formation processes.
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 CitedFormation of the first stars
The first stars were predominantly massive, and understanding their formation is crucial for understanding the early universe and its transformation.
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