White Dwarf

When the triple-alpha process in a red giant star is complete, those evolving from stars less than 4 solar masses do not have enough energy to ignite the carbon fusion process. They collapse, moving down and to the left of the main sequence until their collapse is halted by the pressure arising from electron degeneracy. An interesting example of a white dwarf is Sirius-B, shown in comparison with the Earth's size below. The sun is expected to follow the indicated pattern to the white dwarf stage.



The white dwarf Sirius-B was not seen until 1862, but was predicted in 1844 from the motion of Sirius-A. The blackbody spectrum of Sirius-B peaks at 110 nm, corresponding to a temperature of 26,000 K. From the known absolute magnitudve as the, the radius is calculated to be just 4200 km. Smaller than the Earth, it is almost as massie Sun.

1 teaspoon of a white dwarf would weigh 5 tons. A white dwarf with solar mass would be about the size of the Earth.

At left may be a future white dwarf in Helix Nebula. At right is hot white dwarf NGC2440. Both are surrounded by "cocoons" of the gas they ejected in their collapse toward the white dwarf stage.

White dwarfs in globular cluster M4