Mar 14 2018
A discovery by astronomers shows that irrespective of their size, all galaxies rotate once in every billion years.
This Hubble image reveals the gigantic Pinwheel galaxy, one of the best known examples of “grand design spirals,” and its supergiant star-forming regions in unprecedented detail. The image is the largest and most detailed photo of a spiral galaxy ever released from Hubble. (Image credit: ESA/NASA)
It is well known that one day is the time taken by the Earth to spin around on its axis once, and one year is the length of time taken by the Earth to make a complete orbit around the Sun.
“It’s not Swiss watch precision,” stated Professor Gerhardt Meurer from the UWA node of the International Centre for Radio Astronomy Research (ICRAR).
“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.”
According to Professor Meurer, simple math can be used to show that the average interior density of all galaxies that have the same size is the same.
“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 stated.
Furthermore, Professor Meurer and his colleagues also discovered that older stars occur at the edge of the galaxies.
“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 stated.
“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 the thin smattering of young stars and interstellar gas.”
“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,” stated Professor Meurer.
“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 also stated that futuristic radio telescopes, such as the long-awaited Square Kilometer Array (SKA), will produce huge amounts of data; also, knowledge of the whereabouts of the edge of a galaxy will minimize the processing power required to probe the data.
“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.”