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Representative lifetimes of stars as a function of their masses The change in size with time of a Sun-like star Artist's depiction of the life cycle of a Sun-like star, starting as a main-sequence star at lower left then expanding through the subgiant and giant phases, until its outer envelope is expelled to form a planetary nebula at upper right Chart of stellar evolution
- A Star Is Born
- All About Mass
- Aging Stars
- The Seismology of Stars
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. Before fusion begins, an object that will become a star is known as a young stellar object (YSO), and it passes ...
Once YSOs have contracted and heated enough, fusion of hydrogen into helium begins in their cores and they become main sequence stars. The rate of that fusion increases with the mass of the star, so the most massive stars are the shortest-lived. The lowest-mass stars are known as red dwarfs or M dwarfs. These experience convection — the circulation...
During the post-main-sequence evolution when stars grow huge, they may also pulsate in and out due to instabilities in the outer layers of the stellar envelope. These pulsating stars include the Cepheid variables, used in measuring distances within the Milky Way and to nearby galaxies. In addition, massive stars in the last stages of life are the s...
We can’t see directly into a star’s interior. However, just as earthquakes on Earth’s surface reveal what’s going on inside the planet, the behavior of material on the surface of stars provides researchers with information about the interior. Asteroseismology is the study of vibrations of a star. Naturally, the Sun is the star easiest to study. Res...
It then gradually fades away over many months. After a supernova occurs, a small remnant of the star’s core, made only of neutrons, is left over. This is called a neutron star. A neutron star has a mass of about 1.4 times the mass of the Sun, but is only about 20 km (12.4 miles) in diameter.
After a supernova, some stars leave behind a super dense neutron star, while the heaviest stars leave a black hole. Based on our understanding of stellar evolution, the Sun will start to run out of core hydrogen in about 5 billion years. The Sun will expand, engulfing several of the inner planets, including Earth.
The changes that occur in a star over time and the final stage of its life depends on a star's size. The exact lifetime of a star depends very much on its size. Very massive stars use up their fuel quickly. This means they may only last a few hundred thousand years. Smaller stars use fuel more slowly and will shine for several billion years.
The star is then called a "white dwarf". It can stay like this for a long time. Eventually, it will stop producing any light at all. It is then called a "black dwarf" and it will stay that way forever. Massive stars In large size stars, nuclear fusion will continue until iron is formed. In stars, iron acts like an energy sponge.
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Humans have studied the stars for thousands of years. To many cultures, stars were the metaphor for constancy, while everything else moved and changed. Modern stellar astronomy showed that stars do change on many time scales, ranging from days to longer periods of time than human history. Stars are born, they change over their lifetimes, and ...
