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All stars begin their lives in dense interstellar clouds of gas and dust. Even before they become stars, though, much of their future life and structure is determined by the way they form. A star is defined by nuclear fusion in its core.
- A nebula. A star forms from massive clouds of dust and gas in space, also known as a nebula. Nebulae are mostly composed of hydrogen. Gravity begins to pull the dust and gas together.
- Protostar. As the mass falls together it gets hot. A star is formed when it is hot enough for the hydrogen nuclei to fuse together to make helium. The fusion process releases energy, which keeps the core of the star hot.
- Main sequence star. During this stable phase in the life of a star, the force of gravity holding the star together is balanced by higher pressure due to the high temperatures.
- Red giant star. When all the hydrogen has been used up in the fusion process, larger nuclei begin to form and the star may expand to become a red giant.
Material cast into the cosmos by supernovae and other stellar events will enrich future molecular clouds and become incorporated into the next generation of stars. Astronomers estimate that the universe could contain up to one septillion stars – that’s a one followed by 24 zeros.
The Sun is the closest star to Earth, and the single most important influence on the worlds of the Solar System in terms of the light and particles it emits. Studying the Sun, in other words, helps us understand the habitability of Earth, but also other stars elsewhere in the universe.
Stellar evolution is the process by which a star changes over the course of its lifetime and how it can lead to the creation of a new star.
Oct 3, 2024 · Star - Formation, Evolution, Lifecycle: Throughout the Milky Way Galaxy (and even near the Sun itself), astronomers have discovered stars that are well evolved or even approaching extinction, or both, as well as occasional stars that must be very young or still in the process of formation.
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When the Universe came into existence ~14 billion years ago, the only elements were hydrogen, helium, and traces of lithium, beryllium, and boron. The heavier elements did not yet exist. Heavy elements are produced by nucleosysthesis - the fusion of nuclei deep within the cores of stars.
