"Stellar evolution is the process by which a star changes over the course of time."
Study of the life cycle of stars including birth, death, and various phases in between.
Stellar Birth: Formation and Protostars and Nebulae.
Main Sequence Stars: Main sequence stars are stars that are in a stable phase of their evolution, where they primarily generate energy through nuclear fusion of hydrogen in their cores.
Red Giants: Red Giants are massive, evolved stars in the late stages of stellar evolution that have expanded and cooled, turning reddish in color.
Supernovas: Supernovas are powerful and explosive events that mark the violent deaths of massive stars, resulting in the release of tremendous amounts of energy and sending out shockwaves and expanding debris into space.
White Dwarfs: White dwarfs are dense, hot, and dim stellar remnants that form after low to medium mass stars exhaust their nuclear fuel and shed their outer layers.
Black Holes: Black holes are regions in space where gravity is so strong that nothing, not even light, can escape their powerful grasp.
Neutron Stars and Pulsars: Neutron stars and pulsars are extremely dense remnants of massive stars that have collapsed under their own gravity and emit regular pulses of radiation.
Mass-Luminosity Relationship: The mass-luminosity relationship describes the correlation between a star's mass and its luminosity, providing insights into the energy production and evolution of stars.
Alpha Process: The Alpha Process refers to a series of nuclear reactions in which helium nuclei (alpha particles) fuse to form heavier elements, playing a crucial role in stellar evolution and the creation of elements heavier than helium in stars.
Stellar Structure and Evolution: Stellar Structure and Evolution refers to the study of the internal composition, physical processes, and changes occurring throughout the lifetime of a star.
Protostar Stage: This stage is the initial phase of star formation, where a dense cloud of gas and dust collapses under its own gravity.
Main Sequence Stage: This stage is the most stable and longest-lived phase of a star's life, where it is burning hydrogen in its core.
Red Giant Stage: In this stage, the star expands in size and cools down, as it exhausts its hydrogen fuel in the core.
Horizontal Branch Stage: This stage occurs after the Red Giant stage, where the star shrinks in size and heats up, as the helium in the core begins to fuse.
Asymptotic Giant Branch Stage: In this stage, the star expands again, becoming brighter and cooler, as it burns helium in the core and additional shells around the core.
Planetary Nebula Stage: During this stage, the star's outer envelope is shed into space, revealing the hot core of the star, which eventually becomes a white dwarf.
White Dwarf Stage: A white dwarf is a very dense, small star composed mostly of electron-degenerate matter.
Black Hole Stage: A black hole is formed from the core of a massive star that has undergone gravitational collapse, where the matter has collapsed to an infinitesimal point of infinite density and gravity.
"Depending on the mass of the star, its lifetime can range from a few million years for the most massive to trillions of years for the least massive."
"Trillions of years for the least massive, which is considerably longer than the current age of the universe."
"All stars are formed from collapsing clouds of gas and dust, often called nebulae or molecular clouds."
"Over the course of millions of years, these protostars settle down into a state of equilibrium, becoming what is known as a main-sequence star."
"Nuclear fusion powers a star for most of its existence."
"Initially, the energy is generated by the fusion of hydrogen atoms at the core of the main-sequence star."
"Stars like the Sun begin to fuse hydrogen along a spherical shell surrounding the core."
"This process causes the star to gradually grow in size, passing through the subgiant stage until it reaches the red-giant phase."
"Stars with at least half the mass of the Sun can also begin to generate energy through the fusion of helium at their core."
"Once a star like the Sun has exhausted its nuclear fuel, its core collapses into a dense white dwarf, and the outer layers are expelled as a planetary nebula."
"Stars with around ten or more times the mass of the Sun can explode in a supernova as their inert iron cores collapse into an extremely dense neutron star or black hole."
"Stellar models suggest they will slowly become brighter and hotter before running out of hydrogen fuel and becoming low-mass white dwarfs."
"Stellar evolution is not studied by observing the life of a single star, as most stellar changes occur too slowly to be detected, even over many centuries."
"Astrophysicists come to understand how stars evolve by observing numerous stars at various points in their lifetime."
"Astrophysicists simulate stellar structure using computer models."
"Most stellar changes occur too slowly to be detected, even over many centuries."
"All stars are formed from collapsing clouds of gas and dust, often called nebulae or molecular clouds."
"Once a star like the Sun has exhausted its nuclear fuel, its core collapses into a dense white dwarf."
"Stars with around ten or more times the mass of the Sun can explode in a supernova as their inert iron cores collapse into an extremely dense neutron star or black hole."