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5th of September 2022
A measurement of Hubble’s Constant using Fast Radio Bursts
by James et al.
The expansion of the Universe can be expressed in terms of the Hubble constant, H0. There has been remarkable progress in recent decades in improving the accuracy of H0, however, there remains a tension between measurements of the Hubble constant inferred from Planck observations of the Cosmic Microwave Background (CMB) and those made from calibrating standard candles such as the expanded sample of local type Ia supernovae (SNe Ia). Therefore an independent and robust method of measuring H0 would be a welcome addition to the tools of physical cosmology. Analysis of FRB observations offer such an independent test. Two direct observations of FRBs – dispersion measure (DM) and the signal-to-noise ratio (SNR) – and one inferred property based on host galaxy associations (redshift) provide the set of constraints on H0. There are two, largely independent constraints at work. If FRB energetics are independent of distance, the SNR dependence with redshift is sensitive to H0. This constraint, however, highly depends on the unknown intrinsic distribution of FRB energies. The other constraint is set by the cosmic contribution to the FRB DM. The distribution of FRB DMs and redshifts offer a direct constraint on H0.

James et al. have constrained the value of the Hubble constant by using a detailed model of Fast Radio Burst (FRB) observations from the Australian Square Kilometre Array Pathfinder (ASKAP) and Murriyang (Parkes) radio telescopes. Using a sample of 16 ASKAP FRBs detected by the Commensal Real-time ASKAP Fast Transients (CRAFT) Survey and localised to their host galaxies, and 60 unlocalised FRBs from Parkes and ASKAP, a best-fitting value of H0 is calculated to be 73(+12−8) km/s/Mpc is obtained -- consistent with other measurements but, as expected, with a large uncertainty due to the relatively small sample size. The team used a sample of 100 mock FRBs to demonstrate the accuracy of their model, and the potential for high-precision measurements with the coherent FRB search upgrade to ASKAP (currently in progress), which may help clarify the current Hubble tension in the near future as the sample of FRBs grows exponentially.

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