Why do the spectra of quasars imply that they are extremely distant objects?

Cepheid stars are a common type of star used to measure distance; they all shine in a very tight window of luminosity and therefore provide a baseline for the star being compared. Astronomers use the red/blue shift to measure a star's motion, away/towards us, respectively. Then, they use a star's luminosity against known stars in the foreground and background to ascertain its relative distance.

Quasars have very high redshift values, indicating they are located at vast distances from Earth. Redshift is a property of spectra that is caused by the expansion of the universe. The higher the redshift, the farther away the object is.

The spectra of quasars imply that they are extremely distant objects due to several key observational characteristics:

1. Redshift: Quasars exhibit a significant redshift in their spectra. Redshift occurs when light emitted by an object moves away from an observer, causing its wavelength to elongate toward the red end of the spectrum. This phenomenon is a consequence of the expansion of the universe. The greater the redshift observed in a quasar's spectrum, the farther away it is from Earth.

2. High luminosity: Quasars are among the most luminous objects in the universe, emitting tremendous amounts of energy across a broad range of wavelengths, from radio waves to X-rays. This extraordinary luminosity suggests that quasars are powered by processes involving supermassive black holes in the centers of distant galaxies. Such immense energy output is consistent with objects located at extreme distances.

3. Cosmological distance measures: Astronomers use various methods to estimate the distance to celestial objects, including quasars. These methods often rely on standard candles, such as Type Ia supernovae or certain classes of stars, whose intrinsic brightness is known. By comparing the observed brightness of quasars with their expected luminosity based on these standard candles, astronomers can infer their distances. The results consistently indicate that quasars are located at immense distances from Earth.

Taken together, the redshift, high luminosity, and cosmological distance measures of quasars strongly suggest that they are indeed extremely distant objects, often billions of light-years away from us.

The spectra of quasars exhibit redshifts, indicating that they are moving away from us at very high speeds. According to Hubble's law, the velocity at which a distant object is receding from us is directly proportional to its distance. Since quasars show significant redshifts, it suggests they are moving away from us at velocities corresponding to extreme distances, implying that they are indeed very distant objects.