托福阅读经典加试题目(6)

They also study the spectrum of a star’s light to determine not only the temperature, but also the chemical makeup of the star’s outer layers.

Stellar（恒星的） evolution

The Sun is a type of star known as a main-sequence star. Eventually, main-sequence stars such as the Sun swell into giant stars and then evolve into tiny, dense, white dwarf（矮） stars. Main-sequence stars and giants have a role in the behavior of most variable stars and novas. A star much more massive than the Sun will become a supergiant star, then explode as a supernova. A supernova（超新星） may leave behind a neutron（中子） star or a black hole.

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