This artist’s concept illustrates the two types of spiral galaxies that populate our universe: those with plump middles, or central bulges (upper left), and those lacking the bulge (foreground). Credit: NASA
A large proportion of galaxies have undergone a major ‘metamorphosis’ since they were initially formed after the Big Bang. By providing the first direct evidence of the extent of this transformation, the team hope to shed light on the processes that caused these dramatic changes. They observed around 10,000 galaxies using a survey of the sky created by the Herschel ATLAS and GAMA projects.
The researchers then classified the galaxies into the 2 main types: flat, rotating, disc-shaped galaxies (much like our own galaxy, the Milky Way); and large, oval-shaped galaxies with a swarm of disordered stars. Using the Hubble and Herschel telescopes, the researchers then looked further out into the Universe, and thus further back in time, to observe the galaxies that formed shortly after the Big Bang.
The researchers showed 83% of all the stars formed since the Big Bang were initially located in a disc-shaped galaxy. But only 49% of stars that exist in the Universe today are located in these disc-shaped galaxies – the remainder are located in oval-shaped galaxies ie massive transformation.
A popular theory is that this transformation was caused by many cosmic catastrophes, in which 2 disk-dominated galaxies, straying too close to each other, were forced by gravity to merge into a single galaxy, with the merger destroying the disks and producing a huge pileup of stars. An opposing theory is that the transformation was a more gentle process, with stars formed in a disk gradually moving to the centre of a disk and producing a central pile-up of stars.
“Galaxies are the basic building blocks of the Universe, so this metamorphosis really does represent one of the most significant changes in its appearance and properties in the last 8 billion years.”
Professor Asantha Cooray said: “This study is important as it establishes statistics showing that almost all stars formed in spiral galaxies in the past, but a large fraction of these now appear as large, dead, elliptical galaxies today. This study will require us to refine the models and computer simulations that attempt to explain how galaxies formed and behaved over the last 13 billion years.”
Dr David Clements said: “Up to now we’ve seen individual cases in the local universe where galaxy collisions convert spirals into ellipticals. This study shows that this kind of transformation is not exceptional, but is part of the normal history of galaxy evolution.” http://www.cardiff.ac.uk/news/view/134843-astronomers-unravel-the-history-of-galaxies-for-the-first-time?utm_source=cu-home&utm_medium=News_Feed&utm_campaign=news
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