"Stellar evolution is the process by which a star changes over the course of time."
Life cycle of stars, birth, evolution, and death of stars.
Stellar Formation: The process by which stars are born from clouds of gas and dust.
Protostars: The initial stage of a star's formation, where nuclear fusion has not yet begun.
Main Sequence Stars: The stage of a star's life where fusion of hydrogen into helium occurs, and the star is balanced between gravity and energy production.
Red Giants: The stage of a star's life where fusion of helium is occurring and the star has expanded and cooled.
White Dwarfs: The final stage of a low-mass star's life, where the star has exhausted its nuclear fuel and has collapsed to a very dense core.
Supernovae: The explosive death of a massive star, which can create black holes or neutron stars.
Neutron Stars: The extremely dense, highly magnetized remnants of a supernova.
Black Holes: The result of the collapse of a massive star, creating a singularity with immense gravity.
Binary Stars: A system of two stars orbiting around each other.
Mass Transfer: The process by which material from one star in a binary system is transferred to the other.
Accretion Disks: The formation of a disk of material around a star or black hole, which can lead to the formation of planets or jets of material.
Stellar Winds: The outflow of gas and particles from a star, which can affect the evolution of the star and its surroundings.
Stellar Clusters: Groups of gravitationally bound stars that form together and evolve as a system.
Stellar Populations: The classification of stars based on their age, metallicity, and other characteristics.
Galaxies: Large systems of stars, gas, and dust, which can be used to study the evolution of stellar populations over time.
Cosmology: The study of the universe as a whole, including the history and evolution of galaxies, stars, and other objects.
Protostar: This is the earliest stage of a star's formation characterized by the gradual contraction of gas and dust in a molecular cloud to form what is called a protostar.
T Tauri star: A type of protostar that has reached a stage in which it begins to emit small amounts of visible light as it heats up.
Main-sequence star: Also known as dwarf stars, these are ordinary stars in their most stable state, undergoing nuclear fusion in their cores.
Red giant: These are stars that are no longer in their stable phase as a main-sequence star, but have exhausted their hydrogen fuel and have begun fusion in their outer layers, causing them to expand and cool.
Planetary nebula: This is a process that occurs when a red giant star begins to shed its outer layers, revealing a luminous "shell" of ionized gas called a planetary nebula.
White dwarf: Once all of the outer layers of a planetary nebula have dissipated, what remains is a white dwarf, a small, extremely dense, and hot object that gradually cools over time.
Supernova: If a star has a mass substantially greater than our Sun, it will eventually run out of fuel and undergo a catastrophic explosion as a supernova, which can lead to the formation of a neutron star or black hole.
Neutron star: Formed from the core of a massive star after a supernova explosion, a neutron star is an extremely dense and compact object composed almost entirely of neutrons.
Black hole: This occurs when a star with a mass greater than three times that of our Sun undergoes a supernova explosion and collapses under its own gravity, creating a singularity with an infinitely dense core and surrounded by an event horizon beyond which nothing can escape.
"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."