18th Nov, 2021
Asked 16th Nov, 2021
Are there redshift and luminosity distances for Cepheid Variable stars and RR Lyrae stars?
Do such measurements make sense? Do they exist?
Comparing redshift and luminosity distances, if that is a sensible question, may bear on the 4/3 scaling hypothesis as it relates to dark energy.
All Answers (3)
every measurement makes sense, only their interpretation(s) in the model(s) is up to debate.
The only problem that could occur in my mind is that Cepheids are too "near" us and the redshift measurement is not precise and/or under the resolution of actual made spectrograph, but if the star is far enough and you could make the two measurements (variability period and redshift) the comparison is useful to the famous "ladder problem" in astrophysics (and to make sure you calculate the distance right)
Hi Robert Shour ,
Cepheid and RR Lyrae variables are well known standard candles, and important tools in the cosmological distance ladder. For example, Cepheid variables, which were discovered by Henrietta Swan Leavitt, have the property that their luminosity can be directly inferred by observing their pulsation period, which then allows one to calculate their luminosity distance, given that the observing instrument (telescope) also measures their flux.
However, although nothing stops you from making redshift measurements of relatively nearby objects, this will induce an error in any cosmological parameters inferred from these measurements (such as the luminosity distance), because the peculiar velocities of these objects would be comparable to their Hubble flow, giving you highly inconsistent results. Luminosity distances calculated by interpreting the measured redshifts as cosmological redshifts, become more reliable at large distances, where the Hubble flow dominates over the peculiar velocities.
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