September 2019’s Monthly Media was from Dr Ben McKinley, showing the effect of radio-telescope antenna placement on observing the weak hydrogen signal from the early Universe.

Hydrogen atoms in the early Universe should emit a distinctive radio signal that, if detected, could inform us about the first stars and galaxies and how and when they formed. A component of this signal is constant across the sky and could in principle be detected by a pair of closely-spaced dipole antennas, if the bright foreground emission could be removed.

The antenna configurations are shown in the top left, where the residual signal is shown in the top right after removing the foregrounds by subtracting an 8th order polynomial fit to the data (the simulation contains no hydrogen signal, only foregrounds, however a possible hydrogen signal shape is over-plotted in yellow). The bottom panel shows the root-mean-square of the residuals from above for each antenna configuration.

In the above animation Ben shows a simulation of such an observation, for a number of antenna configurations. By rotating the pairs of antennas, the spatially-varying foregrounds are averaged out as the signal is summed, while the constant hydrogen signal is unaffected.

The more antenna rotations, the better the foregrounds are removed and the greater the chance of detecting the hydrogen signal from the early Universe.