(Sen) - A study of hundreds of galaxies has revealed an unexpected pattern of change that goes back more then half the age of the universe. Astronomers had thought that disk galaxies in the nearby universe had settled into their present form about 8 billion years ago, with little change since. However observations by the Hubble Space Telescope and the Keck telescopes in Hawaii have shown the opposite to be true.
According to NASA's Goddard Space Flight Center astronomer Dr Susan Kassin "the trend we've observed instead shows the opposite, that galaxies were steadily changing over this time period".
Prior to this research, previous studies had removed galaxies that did not look like the well-ordered rotating disks now common in the universe today. Co-author on the paper of the findings Dr Benjamin Weiner, from University of Arizona said "By neglecting them, these studies examined only those rare galaxies in the distant universe that are well-behaved and concluded that galaxies didn't change."
Rotation in galaxies such as our own Milky Way or the Andromeda Galaxy dominates over other internal motion, so they take the form of ordinary disk-shaped systems. Whereas the most distant blue galaxies - their colour indicates stars are forming within them - are very different, they are instead disorganised with motion in multiple directions.
However these blue galaxies show more organised motion and faster rotation speeds the closer they are observed to the present. This means that they are gradually settling into well behaved disk shapes. The trend appears to be true for galaxies of all masses, however the most massive systems show the highest level of organisation.
The researchers say the distant blue galaxies they studied are gradually transforming into rotating disk galaxies like the Milky Way.
Those involved in the study looked at all galaxies with emission lines bright enough to be able to determine internal motions. Emission lines are the discrete wavelengths of radiation emitted by the gas within a galaxy. They are revealed when a galaxy's light is separated into its component colours and carry information about internal motions and distance.
It's believed that the Milky Way galaxy would have gone through the same evolution as the galaxies in the sample, before it gradually settled into its present state at the time the sun and solar system were being formed.
A total of 544 blue galaxies were sampled from the Deep Extragalactic Evolutionary Probe 2 (DEEP2) Redshift Survey, located between 2 billion and 8 billion light years away.
The paper, entitled THE EPOCH OF DISK SETTLING: z ~ 1 TO NOW, is published in The Astrophysical Journal.