Nature's like a photographer's canvas backdrop, lit up by the different types of electromagnetic radiation. Gamma radiation is the most powerful, strong enough to rip your double helix in two. Radio waves are at the low end. They're generally safe, and are almost omnipresent; we live in a sea of radio waves.
While much of the radio waves we're exposed to here on the surface of the Earth come from our own technology—AM/FM radios, WiFi, GPS signals and the like—there are also natural sources. The Universe is bathed in radio waves emitted by things like quasars, active galactic nuclei, supernova remnants, and even planets like Jupiter, which emits more radio waves than the Sun.
Observing radio waves benefits astronomers in several waves. Since radio waves have the longest wavelengths, they pass through dust and gas clouds that block other types of radiation. They can be observed in any weather at all times of the day or night. They reveal different types of physics, and can be observed with interferometers to create high-resolution images. They're particularly useful when it comes to imaging young stars and the planets forming around them, hidden from view in other wavelengths by thick dust.
Australian scientists used radio telescopes to conduct an extensive survey of the Milky Way. It took over 18 months to run and required more than 40,000 hours of supercomputer time to build the observations into one massive image of our galaxy. Different radio wavelengths were mapped to an RGB scheme to make it viewable by human eyes.
The results are in a new paper titled "GaLactic and extragalactic all-sky Murchison Widefield Array survey eXtended (GLEAM-X) III: Galactic plane." It's published in the Publications of the Astronomical Society of Australia. The lead author is Silvia Mantovanini, a PhD student at Australia's Curtin University.
“This low-frequency image allows us to unveil large astrophysical structures in our Galaxy that are difficult to image at higher frequencies.” - Natasha Hurley-Walker, Principal Investigator for GLEAM-X.
The new image is a successor to a previous image released in 2019. While that image came from GLEAM, the GaLactic and Extragalactic All-sky MWA survey, the new one comes from GLEAM-X, the GLEAM eXtended survey. The 2019 image was extragalactic, while the new one focuses on the Milky Way. It also boasts twice the resolution as the previous image, covers twice as much sky, and is ten times more sensitive. The image is a comprehensive view of the Milky Way, and its data will find its way into new research on multiple subjects.
“This vibrant image delivers an unparalleled perspective of our Galaxy at low radio frequencies,” said lead author Mantovanini in a press release. “It provides valuable insights into the evolution of stars, including their formation in various regions of the Galaxy, how they interact with other celestial objects, and ultimately their demise.”
Supernova remnants (SNR) are one type of radio wave emitters, along with emissions in other wavelengths. Mantovanini is particularly interested in SNR and this image will advance both the effort to find more of them and the effort to study them. Hundreds have been found, and astronomers know there must be many more.
But they can be difficult to detect. They resemble different objects like other shells carved out by stellar winds, and even other overlapping, random structures. Finding and studying SNR is important, because they "offer key insights into the life cycle and evolution of stars in our Galaxy," as the authors write in their research.
In their paper, the researcher say they expect to find another 2,000 SNR along the galactic plane. "... we are confident this data release will help find more faint and old elements of the SNR population, helping to fill the current gap," the authors write.
One critical aspect of the new image is that it allows astronomers to discern young stars from SNR, which are both surrounded by gas.
“You can clearly identify remnants of exploded stars, represented by large red circles. The smaller blue regions indicate stellar nurseries where new stars are actively forming,” Mantovanini said.
In some ways, our home galaxy is more difficult to study than other galaxies. While astronomers successfully study other galaxies at extreme distances, we're stuck inside our own galaxy and that presents particular problems. Peering into the galactic center is difficult because we're inside the disk, and extreme concentrations of dust and stars foul our view.
Associate Professor Natasha Hurley-Walker from the same ICRAR team is the principal investigator of the GLEAM-X survey. Hurley-Walker says that the new image will help astronomer make progress in understanding the Milky Way's structure.
“This low-frequency image allows us to unveil large astrophysical structures in our Galaxy that are difficult to image at higher frequencies,” Hurley-Walker said. “No low-frequency radio image of the entire Southern Galactic Plane has been published before, making this an exciting milestone in astronomy.”
This new image won't be the most sensitive and detailed for long. A global collaboration is building the Square Kilometre Array Observatory (SKAO), a powerful radio interferometer that will provide the highest-resolution images in all of astronomy.
“Only the world’s largest radio telescope, the SKA Observatory’s SKA-Low telescope, set to be completed in the next decade on Wajarri Yamaji Country in Western Australia, will have the capacity to surpass this image in terms of sensitivity and resolution,” said Associate Professor Hurley-Walker.