Previously, Astronomers had assumed that galaxies had settled into their current, nicely ordered spiral forms about 8 billion years with little change since then. New observations suggest that instead there has been a constant steady evolution.
In the past, studies charting galaxy evolution had discounted galaxies that dont look like our own nicely ordered spiral Milky Way or Andromeda galaxies – effectively self-selecting the end result of the study to conclude that galaxies dont change over time.
A new study from a team made up of NASA researchers and the University of Arizona has taken a look at deep field galaxies between 8 and 2 billion light years away and discovered that the ancient galaxies are very disordered by comparison – there is a lot of random internal movement compared to older galaxies.
The study shows that as the galaxies get older, these random motions cease and galaxies start to take on the characteristics of an orderly spiral galaxy. In the past 8 billion years, the number of mergers between galaxies large and small has decreased sharply. So has the overall rate of star formation and disruptions of supernova explosions associated with star formation. Scientists speculate these factors may play a role in creating the evolutionary trend they observe.
Now that astronomers see this pattern, they can adjust computer simulations of galaxy evolution until these models are able to replicate the observed trend. This will guide scientists to the physical processes most responsible for the creation of order from disorder.
This article summarised from a press release from NASA. There is a page with a couple of very good videos explaining the study here.
The paper of the study, “The Epoch of Disk Settling: Z~1 To Now” – Susan A. Kassin, Benjamin J. Weiner, S. M. Faber, Jonathan P. Gardner, C. N. A. Willmer, Alison L. Coil, Michael C. Cooper, Julien Devriendt, Aaron A. Dutton, Puragra Guhathakurta, David C. Koo, A. J. Metevier, Kai G. Noeske and Joel R. Primack; is published in the Astrophysical Journal.
EDIT: I’ve also sent an email to Ms. Kassin asking a few questions about the study. I hope I get a response that she will allow to be posted here.