Scientists in Australia studying the universe believe that galaxies rotate with the regularity of clocks - but over periods of a billion years.
A team of astronomers at the University of Western Australia have been exploring the so-called velocity relationship of the universe's galaxies.
They explained that when the Earth spins on its axis, the length of a day is determined. Meanwhile, a year occurs when the planet completes a full orbit of the sun.
Professor Gerhardt Meurer, who worked on the project, said simple mathematical equations suggest that "galaxies of the same size have the same average interior density".
"It's not Swiss watch precision. But regardless of whether a galaxy is very big or very small, if you could sit on the extreme edge of its disk as it spins, it would take you about a billion years to go all the way round," he said.
The idea that galaxies possess similarities can help scientists work out how and when they were formed, suggested the researchers.
"Discovering such regularity in galaxies really helps us to better understand the mechanics that make them tick - you won't find a dense galaxy rotating quickly, while another with the same size, but lower density, is rotating more slowly," he said.
In the study, Meurer and his team discovered that some of the oldest stars in the universe are based towards the edge of large galaxies.
We now know that galaxies rotate once every billion years, with a sharp edge that's populated with a mixture of interstellar gas, with both old and young stars
"Based on existing models, we expected to find a thin population of young stars at the very edge of the galactic disks we studied," he revealed.
"But instead of finding just gas and newly formed stars at the edges of their disks, we also found a significant population of older stars along with a thin smattering of young stars and interstellar gas."
Professor Meurer said this finding can help astronomers focus their observations and identify even more marvels in the universe
"This is an important result because knowing where a galaxy ends means we astronomers can limit our observations and not waste time, effort and computer processing power on studying data from beyond that point," he said.
"So because of this work, we now know that galaxies rotate once every billion years, with a sharp edge that's populated with a mixture of interstellar gas, with both old and young stars."
Professor Meurer explained that when next-generation telescopes such as theSquare Kilometre Array (SKA) are in action, scientists will be able to tap into more data while reducing processing power.
"When the SKA comes online in the next decade, we'll need as much help as we can get to characterise the billions of galaxies these telescopes will soon make available to us," he added.
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