The largest magnetic map of the Universe ever produced – five times larger than all previous efforts combined – marks the beginning of a new generation of research into the field of intergalactic magnetism.
Magnetic fields influence how galaxies grow, how matter moves through space, and how the Universe has evolved over billions of years.
The new map was produced by an international team led by researchers at CSIRO, Australia's national science agency, and the SKA Observatory (SKAO), an intergovernmental organisation building two of the world's largest radio telescopes.
It was the advanced capabilities of CSIRO's ASKAP radio telescope that enabled this research.
Lead researcher Dr Alec Thomson, commissioning scientist with the SKAO, said the scale and density of the map helps us better understand the way energy is distributed across the Universe.
"For the first time, we can investigate fine details of the material between nearby stars, and study a huge number of distant galaxies," he said.
The results are available to the scientific community and the paper has been accepted by Publications of the Astronomical Society of Australia.
CSIRO's ASKAP radio telescope, a precursor to the international SKA telescopes under construction in Australia and South Africa, can see huge areas of the sky at once and at a greater depth than many other telescopes.
It is located at Inyarrimanha Ilgari Bundara, the CSIRO Murchison Radio-astronomy Observatory on Wajarri Yamaji Country in Western Australia, where the SKAO is building the SKA-Low telescope.
ASKAP is used to scan the sky regularly to build highly detailed maps of the Universe's radio signals called the Rapid ASKAP Continuum Surveys (RACS). Multiple surveys have been produced since the first record-breaking RACS complete in 2020, the fastest and largest radio sky survey ever made.
This new map, called SPICE-RACS, works on the principle that light twists as it travels through magnetic fields. By measuring how twisted the light detected by ASKAP was, Dr Thomson and his team could show where magnetic fields were located and their relative strength.
"We collected rotation measures from every galaxy detected in RACS – nearly four million galaxies – and reprocessed this original data from ASKAP to retrieve the full picture," Dr Thomson said.
A magnetic image of this size and scale was previously out of reach, but new technologies such as ASKAP's large field of view and unique dish rotation system, combined with the ability to process huge amounts of different data, have unlocked this new chapter of astronomical investigation.
Professor Naomi McClure-Griffiths, SKAO's Chief Scientist and a member of the research team, is a leader in the study of the Universe's magnetic fields. She said SPICE-RACS is a huge leap forward.
"For the past 20 years we have been working with essentially the same data set, which didn't even cover the southern sky. Now, we can finally answer some big questions with a much better picture of the Universe's magnetic structures," Professor McClure-Griffiths said.
"With the information we now have on magnetic fields throughout the Universe, we can study things like how magnetic fields affect the galactic-scale interaction of our own Milky Way and its neighbours, the Magellanic Clouds. We can even potentially find the answer to questions like when did magnetic fields first appear in the Universe? We had once thought it would be impossible to answer these questions. I'm excited to say that is no longer the case," she said.
CSIRO astronomer Dr Tim Galvin said CSIRO's data access portal, where these maps are kept, is a resource for scientists locally and around the world.
"Our data is accessible to anyone, whether it be for something unique in their own work or to replicate something tested already – an important part of the scientific process," he said.
The data portal, accessed via data.csiro.au, provides access to research data, software and other digital assets published by CSIRO across a range of disciplines, including astronomy.
"The data for this project is already being used by many research teams to produce new insights. By having these resources freely available, we're supporting the continued advancement of our collective understanding of the Universe."
It is only the beginning for this type of research. The international team, called the Polarisation Sky Survey of the Universe's Magnetism (POSSUM) collaboration, are already publishing science results and will continue to produce even better maps over the next few years with ASKAP.
When new telescopes such as the SKA telescopes begin early operations later this decade, these will enable astronomers to chart details of the cosmic web in finer detail and help explain the origin of magnetic fields in the Universe.
