Modern Hubble diagrams are based on observations of which objects?

Modern Hubble diagrams are based on observations of which objects?

• A. Cepheid variables
• B. Type Ia supernovae
• C. Pulsars
• D. Globular clusters

Answer: (B)

The key idea is using standard candles to map distances in the expanding universe. Type Ia supernovae are ideal for this because their peak brightness is very uniform across events once you correct for small differences in their light curves and color. That makes them reliable distance indicators: by observing how bright they appear, you can determine how far away their host galaxies are. Since we can also measure their redshift from spectral lines, these objects let us plot distance versus redshift, creating the Hubble diagram that reveals how the universe is expanding. Cepheid variables are extremely useful for calibrating nearby distances and anchoring the distance scale, but the modern Hubble diagram at cosmological scales relies on Type Ia supernovae because they remain bright enough to be seen at great distances and can be standardized across a wide range of redshifts. Pulsars and globular clusters don’t provide the uniform, bright distance indicators needed for this large-scale expansion plot.

The key idea is using standard candles to map distances in the expanding universe. Type Ia supernovae are ideal for this because their peak brightness is very uniform across events once you correct for small differences in their light curves and color. That makes them reliable distance indicators: by observing how bright they appear, you can determine how far away their host galaxies are. Since we can also measure their redshift from spectral lines, these objects let us plot distance versus redshift, creating the Hubble diagram that reveals how the universe is expanding. Cepheid variables are extremely useful for calibrating nearby distances and anchoring the distance scale, but the modern Hubble diagram at cosmological scales relies on Type Ia supernovae because they remain bright enough to be seen at great distances and can be standardized across a wide range of redshifts. Pulsars and globular clusters don’t provide the uniform, bright distance indicators needed for this large-scale expansion plot.