Researchers at The University of Western Australia node, affiliated with the International Centre for Radio Astronomy Research (ICRAR), have identified a massive structure stretching an astonishing 185,000 light-years between the galaxies NGC 4532 and DDO 137, located about 53 million light-years from Earth. The study was published in the Monthly Notices of the Royal Astronomical Society.
CSIRO’s ASKAP radio telescope on Wajarri Yamaji Country. Image Credit: Alex Cherney/CSIRO
The research additionally disclosed that a massive tail of gas accompanied the bridge, stretching 1.6 million light-years, thus establishing it as the longest ever recorded.
The lead author, Professor Lister Staveley-Smith, an astronomer at ICRAR UWA, stated that this discovery represents a major advancement in comprehending the interactions between galaxies.
Our modelling showed that the tidal forces acting between these galaxies, alongside their proximity to the massive Virgo cluster of galaxies, played a crucial role in the gas dynamics we observed.
Lister Staveley-Smith, Study Lead Author, Professor and Astronomer, ICRAR UWA
“As the galaxies rotated around each other and moved toward the hot gas cloud surrounding the Virgo cluster, which was 200 times hotter than the Sun’s surface, they experienced what is known as ram pressure, which stripped and heated the gas from the galaxies. The process is akin to atmospheric burn-up when a satellite re-enters the Earth’s upper atmosphere, but has extended over a period of a billion years,” said Staveley-Smith.
The density of electrons and the speed at which galaxies are falling into the hot gas cloud are enough to explain why so much gas has been pulled away from the galaxies and into the bridge and surrounding areas.
Lister Staveley-Smith, Study Lead Author, Professor and Astronomer, ICRAR UWA
The observations formed a component of the Widefield ASKAP L-band Legacy All-sky Survey (WALLABY). This extensive initiative aims to chart the sky and examine the distribution of hydrogen gas within galaxies, utilizing the ASKAP radio telescope, which is owned and managed by CSIRO, the national science agency of Australia.
Co-author and ICRAR UWA astrophysicist Professor Kenji Bekki stated that researchers identified the massive gas formations through high-resolution observations of neutral hydrogen.
“Neutral hydrogen plays a crucial role in the formation of stars, making this finding fundamental to understanding how galaxies interact and evolve, particularly in dense environments,” said Professor Bekki.
Professor Staveley-Smith stated that the system exhibits significant similarities to the Milky Way and Magellanic System, offering a distinctive opportunity to examine such interactions in depth.
“Understanding these gas bridges and their dynamics provides critical insights into how galaxies evolve over time, how galactic gas is redistributed, and the varying conditions under which galaxies may or may not form stars,” said Bekki.
This contributes to our broader understanding of the most massive structures in the Universe and their life cycles, which helps us grasp more about their vast complexities and history of star formation.
Kenji Bekki, Study Co-Author and Astrophysicist Professor, ICRAR UWA
Journal Reference:
Staveley-Smith, L., et al. (2025) WALLABY pilot survey: the extensive interaction of NGC 4532 and DDO 137 with the Virgo cluster. Monthly Notices of the Royal Astronomical Society. doi.org/10.1093/mnras/staf1443