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Astronomers Find Answers by Rewinding the Evolution of Galaxies

Astronomers Find Answers by Rewinding the Evolution of Galaxies

by Samburaj DasAugust 27, 2015

A team of astronomers from Cardiff University and a wider group of international scientists have conclusively shown for the first time that galaxies can change their shape and structure over their lifetimes, with evidence to prove the ‘metamorphosis’ of galaxies.

Astronomers from Cardiff University’s School of Physics and Astronomy and a team of international scientists have published a study that concludes galaxies undergo change in their physical structure over the course of their lifetime, with evidence to show for it. The study has been published in the Monthly Notices of the Royal Astronomical Society, as reported by Phys.

The published research article is freely available here.

The collaborative effort helped in observing the present-day sky and then rewinding time by looking through the Herschel and Hubble space telescopes. The team of astronomers discovered that a significant proportion of galaxies has gone through a major ‘metamorphosis’, since the time of being born out of the Big Bang.

Matthew Allen, a Ph.D. student and member of the team at Cardiff University remarked:

This is a huge step in understanding how the galactic population has evolved over billions of years. Using some of the most cutting-edge data and techniques, we are finally beginning to understand the processes that have shaped our Universe.

Milky Way

The Milky Way

Unravelling the Mysteries of Galaxies and the Universe

The astronomers observed nearly 10,000 galaxies in the Universe with the help of a survey of the sky put together by the Hershel ATLAS and GAMA projects.

The group of researchers then classified the galaxies with the two primary types being:

  • Flat, rotating and disk-shaped galaxies (our galaxy, the Milky Way is one such example.)
  • Large, oval-shaped galaxies made with an enormous swarm of disordered stars

To look further back in time, the researchers used the Hubble and Hershel telescopes to observe galaxies formed in the immediate aftermath of the Big Bang.

Here’s what they discovered:

  • 83% of all stars formed after the Big Bang were originally located in a disc-shaped galaxy.
  • Remarkably, only 49% of stars in the Universe today are situated in disk-shaped galaxies, with the rest located in bigger oval-shaped galaxies.

The above numbers suggest a massive transformation or ‘metamorphosis’, where disk-shaped galaxies gradually became oval-shaped galaxies, over time.

Steve Eales, lead author of the study at Cardiff University explained:

“Many people have claimed before that this metamorphosis has occurred, but by combining Herschel and Hubble, we have for the first time been able to accurately measure the extent of this transformation.”

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.

Theories behind the Phenomenon

One popular theory explaining this transformation among galaxies claims rigorous ‘cosmic catastrophes’ to be the cause. In such an event, two disc-shaped galaxies venturing far too close to each other would result in gravity forcing them to merge, becoming a single galaxy. The theory notes that such a merger would destroy the shape of the disks and result in a massive pileup of stars.

An opposing theory stipulates that the transformation is a more gentle process as opposed to a violent coming together, wherein stars in a disc-shaped galaxy move to the centre of the disk resulting in a pile-up of stars in the middle of the galaxy.

Co-authoring the study from the University of California, Professor Asantha Cooray notes the significance of the research, saying:

“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.”

Additionally, Dr David Clements from Imperial College London, also a co-author of the study concludes by noting:

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.

Images from Pixabay.

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