It has taken a million CPU hours, thousands of antennas, and the patience of a doctoral researcher to stitch together the most detailed low-frequency radio color image of the Milky Way ever made. The result is a sprawling mosaic of the Southern Galactic Plane that covers the structure of the galaxy in wavelengths invisible to human eyes but rich with astrophysical information.
The project, led by Silvia Mantovanini at the Curtin University node of the International Centre for Radio Astronomy Research (ICRAR), combined data from two major surveys: the GaLactic and Extragalactic All-sky Murchison Widefield Array (GLEAM) and its successor, GLEAM-X. Conducted with the MWA in Western Australia—a low-frequency radio telescope comprising 4,096 antennas spread over several square kilometers—the surveys mapped the sky between 72 and 231 MHz. GLEAM provided broad coverage while GLEAM-X delivered finer resolution and sensitivity. Mantovanini’s task was to merge them into a single image using advanced image domain gridding algorithms, correcting for ionospheric distortions and aligning thousands of observations into a coherent whole.
The new image offers twice the resolution, ten times the sensitivity, and double the sky coverage compared to the 2019 GLEAM release. This leap in capability enables astronomers to distinguish between different astrophysical phenomena based on their “radio colors.” Large red circles mark supernova remnants-expanding shells of gas and magnetic fields left behind by exploded stars-while smaller blue regions pinpoint stellar nurseries, dense pockets of ionized hydrogen where new stars are forming. The ability to separate these features at a glance addresses a long-standing challenge in Galactic astronomy, where overlapping structures can obscure their origins.
Supernova remnants are of particular interest because they are key sites of cosmic ray acceleration and magnetic field amplification. Hundreds have been cataloged but models suggest thousands remain undetected. Low-frequency radio observations are particularly sensitive to these remnants, since synchrotron emission from relativistic electrons brightens at longer wavelengths. Mantovanini’s work is expected to expand the known population significantly, aiding studies of the Milky Way’s energetic ecosystem.
This same image promises advances in pulsar research. Pulsars, rapidly rotating neutron stars, emit beams of radio waves whose properties vary with frequency. By measuring their brightness across the GLEAM-X bands, astronomers can probe emission mechanisms and refine maps of their distribution within the galaxy. Low-frequency data are very useful in this respect, since they penetrate the dense interstellar medium much better, allowing the detection of pulsars that may well be invisible at higher frequencies.
From a purely technical perspective, the MWA was optimized for large-scale diffuse emission. Short baselines between antennas captured structures as large as 15 degrees across, while longer baselines resolved features down to 45 arcseconds. Complementing GLEAM’s wide-field sensitivity with fine detail provided by GLEAM-X required the joint deconvolution of all visibilities, a process considerably sped up with GPU computation. The high-performance processing was provided by the Pawsey Supercomputing Research Centre, while Mantovanini’s pipeline introduced direction-dependent calibration that better suppressed artefacts coming from bright sources and interference from the atmosphere.
These have resulted in a catalogue of 98,000 radio sources along the Southern Galactic Plane, including pulsars, planetary nebulae, compact H II regions, and distant galaxies beyond the Milky Way. The spectral profile for each source can be analyzed to infer that its emission is either thermal, arising from hot gas, or non-thermal, produced by relativistic particles spiraling in magnetic fields.
Associate Professor Natasha Hurley-Walker, GLEAM-X principal investigator, emphasized the importance of this achievement: “No low-frequency radio image of the entire Southern Galactic Plane has been published before, making this an exciting milestone in astronomy.” She observed that only the future SKA-Low telescope, part of the Square Kilometre Array Observatory, will supersede this image both in sensitivity and resolution. The SKA-Low is to be built on Wajarri Yamaji Country in Western Australia, deploying 131,072 antennas over 74 kilometers, a setup which will take collecting area and baseline diversity to unparalleled dimensions.
For the time being, though, it’s the GLEAM-X mosaic that is the definitive low-frequency view of our Galaxy from the southern hemisphere. In its combination of scale, clarity, and spectral richness, it will be an unrivaled tool for exploring the birthplaces, graveyards, and huge interstellar medium that binds them together within the Milky Way.
