Stellar evolution and nucleosynthesis

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Its **mass**. Low-mass stars end as white dwarfs; high-mass stars end in supernovae, leaving neutron stars or black holes.

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main sequence → **red giant** → **planetary nebula** → **white dwarf**.

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main sequence → **red supergiant** → **supernova** → **neutron star** (or **black hole** if heavy enough).

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The glowing shell of gas a dying **low-mass** star gently puffs off (it has nothing to do with planets).

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The small, hot, dense leftover core of a **low-mass** star after it sheds its outer layers; it just cools over time.

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The violent explosion that ends a **massive** star's life, leaving a neutron star or a black hole.

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The making of **heavier elements** by fusion inside stars (e.g. helium → carbon → ... up to iron in massive stars).

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The Sun fuses only **hydrogen into helium**. A hotter, massive star fuses **heavier elements** (carbon, oxygen...) up to **iron**.

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Heavier nuclei repel more strongly, so fusing them needs a **hotter** core — only a massive star's core gets that hot.

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Fusing up TO iron releases energy, but fusing iron into heavier elements would **cost** energy — so even massive stars can go no further by fusion.

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From its **absorption spectral lines** — each element absorbs its own wavelengths, leaving a unique pattern of dark lines (a fingerprint).

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Its electrons only absorb photons whose energy exactly matches the gaps between its **energy levels**, which are unique to that element.