NASA study finds surprising trend in galaxy evolution
The universe is ever-changing. Just when scientists think they understand something fundamental to the stars, new research challenges those assumptions. It was long accepted that disk-shaped galaxies - like our own Milky Way - attained their shape billions of years ago and were essentially unchanged. But a comprehensive study of hundreds of galaxies reveals an unexpected pattern of change in the cosmos.
Using observations from the Keck telescopes in Hawaii and NASA's Hubble Space Telescope, astronomers looked at distant galaxies similar to our own and found unexpected changes in their shape.
"Astronomers thought disk galaxies in the nearby universe had settled into their present form by about 8 billion years ago, with little additional development since," Susan Kassin, a NASA astronomer and lead researcher of the study, said in a statement. "The trend we've observed instead shows the opposite, that galaxies were steadily changing over this time period."
Eight billion years is more than half the age of the universe. The assumption was that disk-shaped galaxies like the Milky Way and nearby Andromeda Galaxy formed their present shape eons ago, with no new disk galaxies forming afterwards. But the new study found much younger galaxies are still working towards a more stable, disk-shaped form.
So-called blue galaxies - distant galaxies that are still creating stars - have far more chaotic movements within them. The rotation of the galaxies is slower, leading to more internal movement and a less fully-formed shape. The study found a steady shift within these blue galaxies towards a more ordered, disk shape.
By comparing more distant blue galaxies to those closer to Earth, astronomers were able to observe these chaotic galaxies at different points in time and saw a gradual trend towards greater organization.
"Previous studies removed galaxies that did not look like the well-ordered rotating disks now common in the universe today," co-auther Benjamin Weiner, an astronomer at the University of Arizona in Tucson, said in the report. "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."
The team studied 544 blue galaxies from the Deep Extragalactic Evolutionary Probe 2 (DEEP2) Redshift survey, a project that utilizes the Hubble telescope as well as two Earth-based telescopes in Hawaii. The study, which will be published in The Astrophysical Journal, found similarities between the chaotic blue galaxies and our own Milky Way. As the rotation of a galaxy's stars around its center increases, chaotic internal movements decline and the mass will form a more orderly disk shape. Such was the case with our own galaxy.
NASA scientists hope that this new pattern will help astronomers refine computer simulations of galaxy evolution and bring about a greater understand of our still-changing universe.