The central star in a planetary nebula
a. is a main-sequence star.
b. is a pre-main-sequence protostar.
c. is a neutron star.
d. will become a white dwarf.
d
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Absorption lines in the spectra of supergiant stars are broader than the same spectral lines in main sequence stars of the same spectral type
Indicate whether the statement is true or false
What are the latitudes of the tropics of Cancer and Capricorn?
A) 66.5°N and 66.5°S B) 23.5°N and 23.5°S C) 45.0°N and 45.0°S D) 32.5°N and 32.5°S
What change slowly occurs during the main-sequence lifetime of a star?
A) As the solar wind blows material into space, the decreasing mass reduces pressure in the core, which in turn reduces the fusion rate and the luminosity. B) As hydrogen is used up in the core, the fusion rate decreases and reduces the luminosity. C) It gathers more gas from interstellar space, increasing its mass and hence the luminosity. D) Its core temperature slowly increases, increasing the fusion rate and hence the luminosity.
An ice skater doing a spin pulls in her arms, decreasing her moment of inertia by a factor of two. How does her angular speed changes?
A) It is reduced by a factor of two. B) It is reduced by a factor of four. C) It increases by a factor of two. D) It increases by a factor of four. E) It doesn't change.