Life Cycle of a Star

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Gravity Noun

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[grav-i-tee]

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Gravity

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The fundamental force of attraction that causes particles and celestial bodies to aggregate and holds them together in space.

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Example: An apple falls from a tree, demonstrating that gravity is a force that pulls objects downward toward a massive body like Earth.

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Nebula Noun

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[neb-yuh-luh]

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Nebula

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A vast interstellar cloud composed of gas and dust, serving as a nursery where new stars are formed.

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Example: A nebula is a giant cloud of gas and dust in space, often formed from the remnants of a dying star like the one shown.

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Protostar Noun

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[proh-toh-star]

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Protostar

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A young, developing star in its earliest stages, formed from the gravitational condensation of gas and dust before fusion begins.

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Example: A protostar, a very young star, is shown as a hot, dense core gathering gas and dust from a surrounding accretion disk, sometimes shooting out jets.

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Nuclear Fusion Noun

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[noo-klee-er fyoo-zhun]

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Nuclear Fusion

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A nuclear reaction in a star's core where lighter atomic nuclei combine to form heavier nuclei, releasing immense energy.

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Example: This diagram shows how nuclear fusion in a star's core creates an outward pressure that balances the inward pull of gravity, keeping the star stable.

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Main Sequence Noun

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[meyn see-kwens]

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Main Sequence

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The longest and most stable stage in a star's life, during which it actively fuses hydrogen into helium.

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Example: This H-R diagram plots star temperature against brightness, showing that most stars, including our Sun, exist on a diagonal band called the main sequence.

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Red Giant Noun

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[red jahy-uhnt]

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Red Giant

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A luminous, giant star of low or intermediate mass in a late phase of stellar evolution after exhausting its core hydrogen.

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Example: This diagram shows the immense size of a red giant by comparing the Sun's future red giant phase to its much smaller current main-sequence star phase.

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Planetary Nebula Noun

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[plan-i-ter-ee neb-yuh-luh]

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Planetary Nebula

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An expanding, glowing shell of ionized gas ejected from a dying low-mass star during its final evolutionary stages.

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Example: This image shows a real planetary nebula, the glowing shells of gas ejected from a dying, medium-sized star, with the star's core visible at the center.

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White Dwarf Noun

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[wahyt dwawrf]

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White Dwarf

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The hot, dense, planet-sized remnant core of a low-mass star that has exhausted all its nuclear fuel for fusion.

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Example: This is a real photograph showing the bright star Sirius and its tiny, dim companion, Sirius B, which is a white dwarf star.

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Black Dwarf Noun

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[blak dwawrf]

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Black Dwarf

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The theoretical final stage of a white dwarf after it has sufficiently cooled and no longer emits significant heat or light.

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Example: This image shows a black dwarf, the theoretical cold, dark final stage of a star, described as 'The Ashes of Stars' because it no longer shines.

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Red Supergiant Noun

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[red soo-per-jahy-uhnt]

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Red Supergiant

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An extremely large, aging star that is a late evolutionary stage for a high-mass star, among the largest known.

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Example: This diagram shows the enormous size of a red supergiant star by comparing it to the orbits of planets in our solar system.