Life Cycle of a Star

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Stellar Mass Noun

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[stel-er mas]

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Stellar Mass

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The mass of a star, which is the key factor determining its life path, temperature, and fuel consumption rate.

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Example: This diagram shows that a star's life path depends on its starting mass. An average-mass star has a different fate than a high-mass star.

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Nebula Noun

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[neb-yuh-luh]

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Nebula

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A vast cloud of gas and dust in interstellar space from which stars are born through gravitational collapse.

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Example: This image shows a nebula, a giant cloud of gas and dust in space where new stars are born from collapsing material.

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Protoplanetary Disk Noun

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[proh-toh-plan-i-ter-ee disk]

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Protoplanetary Disk

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A rotating, flattened disk of dense gas and dust that forms around a newly developing protostar during star formation.

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Example: A young star is surrounded by a rotating disk of gas and dust, from which planets begin to form by gathering material in their orbit.

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Protostar Noun

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[proh-toh-star]

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Protostar

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The earliest stage of a star's life, formed from a collapsing cloud of gas before nuclear fusion has begun.

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Example: This image shows a protostar, a very young star, gathering mass from a swirling disk of gas and dust surrounding it.

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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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The process that powers a star, where atomic nuclei combine in the core to form heavier nuclei, releasing immense energy.

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Example: Two light atomic nuclei, like hydrogen isotopes, combine to form a heavier nucleus, like helium, releasing a large amount of energy in the process.

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Main Sequence Star Noun

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[meyn see-kwens star]

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Main Sequence Star

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A star in the longest and most stable phase of its life, fusing hydrogen into helium in its core.

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Example: This H-R diagram plots stars by temperature and brightness. Main sequence stars form a long, stable band where most stars spend their lives.

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Radiation Pressure Noun

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[rey-dee-ey-shun presh-er]

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Radiation Pressure

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The outward force exerted by the energy released during nuclear fusion, which counteracts the inward pull of gravity.

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Example: Light from a star carries momentum and exerts a small push, called radiation pressure, on any object it hits, like a reflective surface.

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Luminosity Noun

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[loo-muh-nos-i-tee]

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Luminosity

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The intrinsic brightness of a celestial object, representing the total amount of energy it emits per unit of time.

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Example: This H-R diagram plots stars to show their luminosity (brightness) on the vertical axis, demonstrating how different types of stars have different luminosities.

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Absolute Magnitude Noun

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[ab-suh-loot mag-ni-tood]

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Absolute Magnitude

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A measure of a star's actual brightness as if it were viewed from a standard distance of 10 parsecs.

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Example: This diagram shows a scale of absolute magnitude, comparing the brightness of our Sun to other stars. Brighter stars have lower, even negative, numbers.

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Hertzsprung-Russell (HR) Diagram Noun

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[herts-sprung rus-uhl dai-uh-gram]

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Hertzsprung-Russell (HR) Diagram

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A chart that plots stars according to their luminosity and surface temperature, revealing key patterns in stellar evolution.

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Example: This diagram, called a Hertzsprung-Russell (HR) diagram, sorts stars by their temperature and brightness, showing where different types like giants, dwarfs, and main-sequence stars exist.