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Astronomers studying the outskirts of a distant galaxy have discovered the galaxy sits in a serene ocean of gas.

The massive galaxy, which is about four billion light years from Earth, is surrounded by a halo of gas that is much less dense and less magnetised than expected.

The finding was published today in the journal Science.

Co-author Associate Professor Jean-Pierre Macquart, from the 麻豆直播 node of the International Centre for Radio Astronomy Research (ICRAR), said gas on the outskirts of galaxies has traditionally been hard to study.

鈥淭he halo of gas can actually extend out 10 times further than the stars in a galaxy, and can contain a substantial amount of the matter that鈥檚 in a galaxy,鈥� he said.

鈥淏ut it鈥檚 very difficult to see the gas directly with a telescope.鈥�

Associate Professor Macquart said this discovery was made using a new technique involving fast radio bursts鈥攑owerful flashes of energy from deep space.

鈥淔ast radio bursts come from all over the sky and last for just milliseconds,鈥� he said.

鈥淭hey involve incredible energy鈥攅quivalent to the amount released by the Sun in 80 years.

鈥淲e鈥檙e not sure what causes them, and have only recently been able to pinpoint the galaxies they come from.鈥�

Associate Professor Macquart said the research team looked at how a single fast radio burst distorted as it travelled five billion light years through the Universe.

Along the way, the burst shot through a galaxy鈥檚 halo of gas, like a lighthouse鈥檚 beam cutting through fog.

Associate Professor Macquart said the researchers expected the signal from the fast radio burst to be distorted by the galaxy.

鈥淚f you go out on a hot summer鈥檚 day, you see the air shimmering and the trees in the background look distorted because of the temperature and density fluctuations in the air,鈥� he said.

鈥淭hat鈥檚 what we thought would happen, that the signal from the fast radio burst would be completely distorted after passing through the hot atmosphere of the galaxy.

鈥淏ut instead of the stormy galactic 鈥榳eather鈥� we were expecting, the pulse we observed had travelled through a calm sea of unperturbed gas.鈥�

The finding suggests that galaxy halos are much more serene than previously thought, with gas that is less turbulent, less dense and less magnetised than expected.

One reason astronomers are so interested in galaxy halos is because they can help us understand why material is ejected from galaxies, causing them to stop growing.

University of California Professor of Astronomy and Astrophysics J. Xavier Prochaska, who led the research, said halo gas provides a fossil record of these ejection processes.

鈥淪o our observations can inform theories about how matter is ejected and how magnetic fields are transported from the galaxy,鈥� he said.

Professor Prochaska said the team now plans to test other galaxies.

鈥淥ur research appears to reveal something entirely new about galactic halos,鈥� he said.

鈥淯nless of course this galaxy happens to be just some weird exception鈥攁nd with only one object you can鈥檛 be sure about that.鈥�

The research used a fast radio burst that was detected in November by CSIRO鈥檚 Australian Square Kilometre Array Pathfinder (ASKAP), in outback Western Australia.

The telescope is a precursor to the Square Kilometre Array (SKA), which will be the world鈥檚 largest radio telescope when it鈥檚 built in the next decade.

The study was led by Professor Xavier Prochaska from the University of California and involved 19 researchers from around the world.