LIFE CYCLE OF A STAR

The giant cloud of gas and dust from which stars are born.

What is a nebula?

The main gas that makes up most of a nebula and, later, a star.

What is hydrogen?

The dense, hot clump formed as a collapsing cloud heats up, before nuclear fusion begins.

What is a protostar?

The process of combining light atomic nuclei into heavier ones, releasing enormous energy.

What is nuclear fusion?

The core temperature (approximately) needed for hydrogen fusion to begin.

What is about 10 million Kelvin?

The stable, longest stage of a star's life, where hydrogen fuses into helium in the core.

What is the main sequence?

The current life stage of our Sun.

What is the main sequence?

The approximate current age of our Sun.

What is about 4.6 billion years?

The approximate time remaining before our Sun leaves the main sequence.

What is about 5 billion years?

The general rule connecting a star's mass to its lifespan.

What is, the more massive the star, the shorter its life?

The chart that plots stars by temperature and brightness (luminosity), used to classify their life stage.

What is the Hertzsprung-Russell (HR) Diagram?

The stage a low-mass star enters once core hydrogen runs out, becoming large and reddish.

What is a red giant?

The three planets a red giant Sun is predicted to expand enough to engulf.

What are Mercury, Venus, and possibly Earth?

The fusion process in a red giant's core that produces carbon and oxygen.

What is helium fusion?

The glowing shell of gas shed by a dying low-mass star, historically misnamed since it has nothing to do with planets.

What is a planetary nebula?

The small, dense, hot stellar remnant left after a low-mass star sheds its outer layers.

What is a white dwarf?

The maximum mass a white dwarf can have before it would collapse further.

What is the Chandrasekhar Limit (about 1.4 solar masses)?

The theoretical final cooled state of a white dwarf, not yet observed to exist due to the universe's age.

What is a black dwarf?

The expanded, late-life stage of a high-mass star, larger than a red giant.

What is a red supergiant?

The heaviest element a massive star's core can fuse before fusion stops producing outward energy.

What is iron?

The reason iron halts fusion in a massive star's core.

What is, iron fusion absorbs energy instead of releasing it?

The massive explosion triggered by the sudden collapse of a high-mass star's iron core.

What is a supernova?

The famous nearby supernova observed in 1987, visible to the naked eye.

What is SN 1987A?

The historical supernova observed by Chinese astronomers in 1054 AD, whose remnant is now visible.

What is SN 1054 (source of the Crab Nebula)?

The expanding cloud of debris left behind after a supernova explosion.

What is a supernova remnant?

The process responsible for scattering heavy elements like gold and silver throughout the universe.

What is a supernova explosion (stellar nucleosynthesis)?

The extremely dense remnant formed when a collapsed stellar core is between about 1.4 and 3 solar masses.

What is a neutron star?

A rapidly spinning neutron star that emits beams of radiation, detected as regular pulses.

What is a pulsar?

The object formed when a collapsed stellar core exceeds about 3 solar masses.

What is a black hole?

The boundary around a black hole beyond which nothing, not even light, can escape.

What is the event horizon?

The radius that defines the size of a black hole's event horizon.

What is the Schwarzschild radius?

The famous supermassive black hole first directly imaged in 2019, located in galaxy M87.

What is the black hole at the center of Messier 87 (M87*)?

The unit used to compare the mass of stars to our Sun.

What is a solar mass?

The process by which stars create new elements through fusion, especially in later life stages and supernovae.

What is stellar nucleosynthesis?

A star with too little mass to sustain hydrogen fusion, sometimes called a 'failed star.'

What is a brown dwarf?

A young, still-forming star that has not yet begun stable hydrogen fusion.

What is a T Tauri star?

A system of two stars orbiting a common center of mass.

What is a binary star system?

The outer, visible surface layer of the Sun that emits most of its light.

What is the photosphere?

The Sun's outermost layer of hot, thin plasma, visible during a total solar eclipse.

What is the corona?

The stream of charged particles continuously released from the Sun's corona into space.

What is the solar wind?

The classification system for stars using the letters O, B, A, F, G, K, M, from hottest to coolest.

What is the stellar spectral classification (OBAFGKM)?

The spectral class of our Sun.

What is class G (a G-type main sequence star, or yellow dwarf)?