A team of researchers and engineers have made the most precise measurement yet of low-frequency background radio emissions from space, paving the way for new astronomical discoveries.

The work updates measurements that have remained largely unchanged since the 1960s, revealing the sky is significantly brighter than previously believed. This measurement provides a new benchmark that will ensure observations by current and future telescopes can be accurately interpreted to expand our understanding of the Universe.

A single antenna from the SKA Observatory’s SKA-Low telescope was used for this measurement, placed on a large tile of steel mesh at Inyarrimanha Ilgari Bundara, our Murchison Radio-astronomy Observatory on Wajarri Yamaji Country. This configuration captured signals from a large portion of the sky simultaneously. Unlike traditional observations that focus on specific celestial objects such as black holes, galaxies or stars, this approach measured the combined radio glow of the sky across a broad band of radio frequencies.

The experimental data was compared to the Global Sky Model (GSM). The GSM is a model of the radio sky that includes the brightness (a measure of radio power) and structure of radio measurements as they are seen on Earth at a wide range of frequencies. The measurement was compared to a theoretical spectrum the same antenna would make if it were under a sky perfectly represented by the GSM, and it was found that the measured spectrum was about 20% than brighter than previously estimated.

This correction has important implications for cosmology and for models of the Universe’s evolution. It also provides a primary calibration reference for the SKA-Low telescope, currently under construction at the same site, which will be one of the largest radio telescopes in the world. Accurate calibration is essential for converting SKA-Low telescope observations into something meaningful, and this new measurement will be crucial in achieving this goal.

The experiment was part of the Global Imprints from Nascent Atoms to Now (GINAN) project and used a novel custom-built radiometer, designed and constructed by CSIRO. During measurements, the radiometer can dynamically calibrate itself every few minutes and can determine the reflection error of the incoming radio waves as they enter the receiver. It can also determine the power and spectral shape of electrical noise it generates in the process. These values and errors are calculated independently for each calibration cycle and each frequency channel, ensuring stability and accuracy throughout the observation. Once they are removed in post processing, a corrected spectrum of incoming radio waves from space is produced with a high degree of confidence. The capabilities of this radiometer are so innovative, that the technology has now been patented.

More details can be found in the preprint of the paper here: https://arxiv.org/abs/2509.11846