Radio telescopes reveal Milky Way's supernova remnants

A research team led by Macquarie University and Italy’s National Institute of Astrophysics (INAF) has used Australia’s two greatest radio telescopes to create the most detailed radio image yet of the Milky Way galaxy, showcasing remnants of star births and deaths.

Radio observations of a large section of the galactic plane of the Milky Way were conducted with the ASKAP radio telescope and the Parkes radio telescope, Murriyang, both owned and operated by CSIRO, as part of the PEGASUS and EMU (Evolutionary Map of the Universe) surveys. This is the first joint image to be released by the survey teams and may be able to answer the question “Where are all the supernova remnants?” — a question that has troubled astronomers for some time.

Supernova remnants are what is left when a star dies. Models predict that, due to the age and density of the Milky Way, we should see the remnants of many, many stars that have lived and died. However, we have not yet had telescopes sensitive enough to detect these remnants, and scientists need to detect five times more remnants than are currently documented to match predictions.

The PEGASUS survey is one of the many projects building on the EMU and POSSUM projects, which both use ASKAP to learn more about our cosmos. Macquarie University Professor Andrew Hopkins, lead scientist of the EMU project, said the new composite image shows the galactic plane in its finest detail yet.

“This new picture showcases a region of the Milky Way, only visible to radio telescopes, where we can see extended emission associated with hydrogen gas filling the space between dying stars, related to the birth of new stars, and hot bubbles of gas called supernova remnants,” Hopkins said. “Over 20 new possible supernova remnants have been discovered as a result of combining these images, where only seven were previously known.”

The individual radio telescope images side by side. ASKAP image credit (left): R Kothes (NRC) and the EMU and POSSUM teams. Parkes image credit: E Carretti (INAF) and the PEGASUS team.

PhD student Brianna Ball, from the University of Alberta, has conducted the work to help discover these new possible supernova remnants. It was her supervisor, Roland Kothes of the National Research Council Canada (NRC), who put the image together.

“When Roland combined the PEGASUS map with that from the EMU and POSSUM observations, the result was marvellous; when we opened the image for the first time, we were amazed by such quality and beauty,” said PEGASUS project leader Ettore Carretti, from INAF.

“PEGASUS has captured a large region of the galactic plane of our galaxy full of supernova remnants, regions of ionising hydrogen and planetary nebulae, which, thanks to the combination of data from the ASKAP and Parkes telescopes, can be studied with extremely high precision and accuracy.”

With the quality of the new image being extremely clear, Hopkins believes astronomers will be able to firm up their understanding of the galaxy and beyond with future observations.

“The eventual results will be an unprecedented view of almost the entire Milky Way, about a hundred times larger than this initial image, but achieving the same level of detail and sensitivity. It is estimated that there may be about 1500 more supernova remnants in the galaxy that astronomers haven’t discovered yet. Finding the missing remnants will help us unlock more of an understanding of our galaxy and its history,” he said.

Top image: Both radio telescope images merged together. Image credit: R Kothes (NRC) and the PEGASUS team.