The Major Advantages of the 21-Cm Radio Emission from Hydrogen

question 224

Multiple Choice

The major advantages of the 21-cm radio emission from hydrogen gas for investigating the spiral structure of our Galaxy are that:

• A) it is relatively easily absorbed by hydrogen gas in the Milky Way, so measurements are not confused by emission of this radiation from other galaxies beyond the Milky Way. It originates only from cold hydrogen gas and can be used to map this important component.
• B) radio waves easily penetrate the Milky Way dust and gas, and they are a very narrow-wavelength line emission; thus, its Doppler shift can be used to measure gas motions.
• C) Doppler shift of this narrow-wavelength line emission is caused by the temperature of the hot hydrogen gas and therefore can be used to measure the distribution and temperature of this important component of the Milky Way.
• D) this emission can easily penetrate the Milky Way gas and dust and comes only from hot gas, hence its ability to be used to map the distribution of hot hydrogen gas.

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Definitions:

Pentanoic Acid

A short-chain fatty acid with five carbon atoms, also known as valeric acid, with a strong, pungent odor.

Pimelic Acid

A dicarboxylic acid with a seven-carbon chain, functioning as a precursor in the biosynthesis of lysine.

Alkene

A hydrocarbon containing at least one carbon-carbon double bond, characterized by the general formula CnH2n.

Cyclohexene

A cyclic hydrocarbon with the formula C6H10, characterized by the presence of a double bond in the ring structure.