Dr. Aaron Titus | Department of Physics, High Point University
PHY1050      Astronomy of Stars, Galaxies, and the Cosmos
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death of low-mass stars

The "death of a star," meaning what happens to a star after its life on the main sequence, depends on its mass.

Low mass main-sequence stars (with main-sequence mass less than 10 solar masses or so) undergoe the following phases: red giant, then planetary nebula, then white dwarf.

As a low-mass main-sequence star (of mass less than 10 solar masses) exhausts its supply of hydrogen, it expands and cools. We call the star in this phase a red giant.

As the outer layers of the star's atmosphere continue to expand, we call the resulting cloud a planetary nebula.

At the center of the planetary nebula is the core of the star. The core's mass is less than 1.4 solar masses. The core of the star gravitationally contracts and increases in temperature, until reaching equilibrium where the particles of the star are packed so closely together that electrons cannot be packed more tightly. The star is now called a white dwarf.

Our Sun will follow this evolutionary path. The diameter of a white dwarf is about 1/100th of the diameter of the main sequence star it evolved from. Its volume, then, is about one millionth its original volume. Thus, a white dwarf is VERY dense, one of the most dense objects in the universe (though we'll discover a few objects more dense.)

The gravitational contraction of a white dwarf produces very high temperature. However, because its radius is so small, a white dwarf does not radiate very much energy per second and thus has a very low luminosity.

Eventually, the white dwarf will exhaust its fuel and cool until it cannot be seen. By this time, all elements in the periodic table from hydrogen to iron would have been produced by fusion sometime in the life of the star from main sequence phase to its white dwarf phase.

 

 

 

 

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