Planetary Nebulae and White Dwarfs

Planetary nebulae, despite their name, are not related to planets. The term was coined by William Herschel when he discovered the Saturn Nebula, as its appearance reminded him of Uranus. These nebulae are formed when a dying low-mass star expels its outer layers, creating a glowing shell of gas and dust. This process plays a significant role in the chemical evolution of galaxies by returning enriched material to the interstellar medium. There are approximately 20,000 planetary nebulae in our galaxy, but only 1,800 have been cataloged. At the center of these nebulae lies a white dwarf, a dense remnant of the star, emitting mostly ultraviolet light due to its high surface temperature.

Why did William Herschel name the Saturn nebula a 'planetary nebula'?

• As it was discovered near the planet Uranus

• Because of its blue-green tint and round shape

• Due to its resemblance to the planet Saturn

• Because it is related to planets

What happens to a low-mass star at the end of its life cycle?

• It expands into a red giant and forms a planetary nebula

• It becomes a black hole

• It explodes as a supernova

• It remains unchanged

How long does the expanding shell of gas from a planetary nebula last?

• About 200,000 years

• About 20,000 years

• About 2 million years

• About 2,000 years

What is the significance of planetary nebulae in galaxies?

• They create new stars

• They enrich the interstellar medium with heavy elements

• They absorb light from nearby stars

• They prevent the formation of black holes

Approximately how many planetary nebulae have been catalogued in our galaxy?

• 1,800,000

• 180,000

• 18,000

• 1,800

What is a notable characteristic of the white dwarf at the center of a planetary nebula?

• It emits mostly infrared light

• A spoonful of its material can weigh as much as a truck

• It is less dense than a neutron star

• It is larger than the Earth

What type of light do white dwarfs primarily emit?

• Infrared light

• Visible light

• Ultraviolet light

• X-rays

What is the minimum surface temperature of a white dwarf?

• 8,500,000 degrees Kelvin

• 8,500 degrees Kelvin

• 85,000 degrees Kelvin

• 850,000 degrees Kelvin