EDGES 21cm Result Questioned

Not so long ago, in  results published in 2018, the EDGES radio telescope in Australia made an observation of a particular signal that strongly contradicted prevailing theoretical expectations about "cosmic dawn." A new paper argues based upon another radio telescope observation, that this interpretation of what EDGES saw was incorrect, because their observations could not replicate the EDGES observation.

This is particularly notable because the EDGES result, if correct, is one of the most damning challenges to the LambdaCDM Standard Model of Cosmology at the cosmology scale. If it has been misinterpreted, that significantly strengthens the LambdaCDM model's cosmology problems (while still leaving its serious galaxy scale problems unresolved and still leaving in place some independent cosmology scale problems that are conceivably easier to remedy that the stark contradiction of the EDGES result).

The astrophysics of the cosmic dawn, when star formation commenced in the first collapsed objects, is predicted to be revealed by spectral and spatial signatures in the cosmic radio background at long wavelengths. The sky-averaged redshifted 21 cm absorption line of neutral hydrogen is a probe of the cosmic dawn. The line profile is determined by the evolving thermal state of the gas, radiation background, Lyman α radiation from stars scattering off cold primordial gas, and relative populations of the hyperfine spin levels in neutral hydrogen atoms. We report a radiometer measurement of the spectrum of the radio sky in the 55–85 MHz band, which shows that the profile found by Bowman et al. in data taken with the Experiment to Detect the Global Epoch of Reionization Signature (EDGES) low-band instrument is not of astrophysical origin; their best-fitting profile is rejected with 95.3% confidence. The profile was interpreted to be a signature of the cosmic dawn; however, its amplitude was substantially higher than that predicted by standard cosmological models. Our non-detection bears out earlier concerns and suggests that the profile found by Bowman et al. is not evidence for new astrophysics or non-standard cosmology.

Singh, S., Nambissan T., J., Subrahmanyan, R. et al., "On the detection of a cosmic dawn signal in the radio background." Nature Astronomy (February 28, 2022). https://doi.org/10.1038/s41550-022-01610-5

The journal also has a story explaining the claims of the new paper for a wider audience. The EDGES group argues that the systemic error could just as easily be from the group behind the new paper as from their own observations.