The spectral line of hydrogen producing the quasar...

The spectral line of hydrogen producing the quasar absorption lines in most studies has a laboratory wavelength of $122 \mathrm{nm}$. If a hydrogen cloud is at a distance of 1 billion ly, a. use Hubble's law to find the recession velocity of this cloud. b. what is the redshift of the cloud? c. at what wavelength will the absorption occur?

The spectral line of hydrogen producing the quasar absorption lines in most studies has a laboratory wavelength of $122 \mathrm{nm}$. If
a hydrogen cloud is at a distance of 1 billion ly,
a. use Hubble's law to find the recession velocity of this cloud.
b. what is the redshift of the cloud?
c. at what wavelength will the absorption occur?

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Key Concepts

Hubble's Law

Hubble's Law relates the recession velocity of distant astronomical objects to their distance from the observer. It is expressed as v = H? × d, where H? is the Hubble constant. This concept is fundamental in cosmology as it provides evidence for the expansion of the universe and allows astronomers to estimate distances based on observed recession speeds.

Cosmological Redshift

Cosmological redshift occurs due to the expansion of space itself, which stretches the wavelength of light as it travels through the universe. It is quantitatively defined as z = (?_obs - ?_emit) / ?_emit, where ?_emit is the rest (or laboratory) wavelength and ?_obs is the observed wavelength. This shift is a key observable in determining the velocity and distance of extragalactic objects.

Spectral Absorption Lines

Spectral absorption lines result when light from a background source passes through a cooler intervening medium, which absorbs light at specific wavelengths corresponding to atomic transitions. In the context of hydrogen clouds absorbing light along the line of sight to distant quasars, these lines are used to probe the properties of the intergalactic medium and the effects of cosmological expansion on the wavelengths observed.

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