Stellar life cycles

Objective: Explain nebula and protostar, distinguish their meanings, and apply them to a described case.

Nebula: A nebula is a cloud of gas and dust that can include regions of star formation. Protostar: A protostar is a contracting young stellar object before stable main-sequence hydrogen fusion. A star's evolution reflects changing energy production and its response to gravity. Core hydrogen fusion defines the main-sequence phase, and later stages depend strongly on initial mass and material loss. Higher-mass stars generally consume their fuel more rapidly rather than necessarily living longer because they contain more fuel. Not every star becomes a supernova or a black hole. Distinguish observable stages from compact remnants and their formation pathways. Application: Gravity compresses part of a cold interstellar cloud. This most directly illustrates nebula. A collapsing cloud core heats as it contracts. This most directly illustrates protostar.

Objective: Explain main sequence and red giant, distinguish their meanings, and apply them to a described case.

Main sequence: A main-sequence star sustains hydrogen fusion in its core with approximate balance between gravity and pressure. Red giant: A red giant is an expanded later stage reached by many stars as their internal fuel conditions change. A star's evolution reflects changing energy production and its response to gravity. Core hydrogen fusion defines the main-sequence phase, and later stages depend strongly on initial mass and material loss. Higher-mass stars generally consume their fuel more rapidly rather than necessarily living longer because they contain more fuel. Not every star becomes a supernova or a black hole. Distinguish observable stages from compact remnants and their formation pathways. Application: A star steadily fuses core hydrogen for much of its life. This most directly illustrates main sequence. A Sun-like star expands after core hydrogen becomes depleted. This most directly illustrates red giant.

Objective: Explain white dwarf and massive-star fate, distinguish their meanings, and apply them to a described case.

White dwarf: A white dwarf is a compact stellar remnant supported largely by electron degeneracy pressure. Massive-star fate: Many massive stars undergo core collapse and may leave neutron stars or black holes, with outcomes depending on their properties. A star's evolution reflects changing energy production and its response to gravity. Core hydrogen fusion defines the main-sequence phase, and later stages depend strongly on initial mass and material loss. Higher-mass stars generally consume their fuel more rapidly rather than necessarily living longer because they contain more fuel. Not every star becomes a supernova or a black hole. Distinguish observable stages from compact remnants and their formation pathways. Application: A Sun-like star leaves a dense remnant after losing outer layers. This most directly illustrates white dwarf. A massive star ends in a core-collapse supernova. This most directly illustrates massive-star fate.