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Planetary Nebula

General Information

  1. As stars begin to die, they expand to become red giants.

  2. At the end of the red giant phase the star gently puffs off its outer layers. These outer layers form the planetary nebula.

  3. The gas moves away from the star with speeds of 6-20 miles per second (10-30 kilometers/second). After 50-100 thousand years, the shell of gas has moved far enough from the star so it no longer shines.

  4. Only about 10% of the star is puffed off. The rest of the star shrinks until it is about the size of the Earth. This star is called a white dwarf.

  5. White dwarfs are no longer generating any energy so they will cool off and eventually become black.

  6. White dwarfs contain as much matter as the sun but are Earth-sized. One teaspoon of white dwarf star stuff brought to Earth would weigh as much as a couple dozen elephants.

  7. There are probably between 20 and 50 thousand planetary nebulae in our galaxy.

  8. Our sun will begin this process in 4-5 billion years.

    a. The sun will expand to become a red giant

    b. When the sun becomes a red giant the Earth’s atmosphere and oceans will be evaporated into space.

    c. There is a chance the whole Earth might evaporate.

    d. What remains of the sun will then become a white dwarf in about 5 billion years.

  9. Planetary Nebulae have nothing to do with planets. Antoine Darquier discovered the second planetary nebulae every known, M57 (the Ring Nebula), and compared it to a “fading” planet. William Herschel actually invented the name “Planetary Nebula” because these objects reminded him of the planet he had discovered, Uranus.

  10. Planetary Nebulae are actually brighter visually than photographically. 90 - 95% of the visible light they emit are in one single emission line! This line occurs in the green part of the light spectrum, where human eyes are the most sensitive, and film is less sensitive. (The spectral line is a “forbidden” line of doubly ionized oxygen. In “normal” situations, this line is never seen, but because of the physical situation of the nebula, light can be emitted at this wavelength.)
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References
Item Updated Notes
additional info from 2017-05-01 http://messier.seds.org/planetar.html