Is there a standard measuring rod in the Universe?

TL;DR

This paper uses VLBI observations of compact radio sources to construct an angular-diameter/redshift diagram, deriving cosmological parameters consistent with current models and highlighting the role of relativistic beaming.

Contribution

It presents a novel analysis of VLBI data to measure cosmological parameters and emphasizes the significance of relativistic effects in interpreting compact radio sources.

Findings

Cosmological parameters align with existing consensus values.

The angular-diameter/redshift diagram reveals expected cosmological features.

Relativistic beaming significantly influences observed source properties.

Abstract

The Caltech-Jodrell Bank very long baseline interferometry (VLBI) Surveys give detailed 5 GHz VLBI images of several hundred milliarcsecond (mas) radio sources, and the full width at half-maximum angular sizes of the corresponding compact cores. Using the latter, I have constructed an angular-diameter/redshift diagram comprising 271 objects, which shows clearly the expected features of such a diagram, without redshift binning. Cosmological parameters are derived which are compatible with existing concensus values, particularly when the VLBI data are combined with recent Baryon Accoustic Oscillations observations; the figures are presented as indications of what might be expected of larger samples of similar data. The importance of beaming and relativistic motion towards the observer is stressed; a model of the latter indicates that the emitting material is close to the observer's line of sight and moving with a velocity which brings it close to the observer's rest frame. With respect to linear size, these objects compare well in variance with type Ia supernovae; the efficacy of the latter is improved by the brighter-slower and brighter-bluer correlations, and by the inverse-square law.