planetary nebula

Thân thiện

A planetary nebula glows brightly in the depths of space.

Definition

Noun: A planetary nebula is a type of astronomical object consisting of a glowing shell of ionized gas and plasma ejected from a red giant star in the late stages of its evolution. Despite the name, it has no relation to planets; the term originates from early astronomers who observed their round, planet-like appearance through small telescopes. At its center lies a very hot, dense stellar remnant known as a white dwarf, whose intense ultraviolet radiation causes the surrounding expanding envelope of gas to fluoresce.

Usage Examples

• Noun:
  • The Ring Nebula (M57) is a famous example of a planetary nebula.
  • Astronomers study the chemical composition of a planetary nebula to understand stellar evolution.
  • The star will eventually shed its outer layers to form a planetary nebula.

Advanced Usage

• "To be in the planetary nebula phase": Refers to the specific, relatively brief stage (typically tens of thousands of years) in a star's life cycle when it appears as a planetary nebula.
  • Our Sun will enter the planetary nebula phase in about five billion years.

Variants and Related Words

• Nebula (n): A general term for a cloud of gas and dust in interstellar space. A planetary nebula is a specific subtype.
• White dwarf (n): The hot, compact stellar core remnant left at the center of a planetary nebula.
• Protoplanetary nebula (n): A distinct, short-lived phase that sometimes precedes the formation of a true planetary nebula, where the star is not yet hot enough to ionize the ejected gas.

Synonyms

• Emission nebula: A broad category of nebulae that emit their own light due to energetic radiation, which includes planetary nebulae. (Note: Not all emission nebulae are planetary nebulae; others include H II regions like the Orion Nebula).

Related Phrases/Idioms

(This term is a specific scientific noun; it is not commonly used in idiomatic or phrasal verb constructions.)

Học thuật

Noun

1. a nebula that was once thought to be a star with its planets but is now thought to be a very hot star surrounded by an expanding envelope of ionized gases that emit a fluorescent glow because of intense radiation from the star