It seems counterintuitive that there would be mature galaxies when the Universe was very young. However, an international team of astronomers have discovered fifteen galaxies that were already fully mature only 1.6 billion years after the big bang. Much of what we have known about star and galaxy formation states that the maturation process takes quite a long time, which means that some galaxies may age differently than what is predicted by traditional models. The results were published in The Astrophyiscal Journal Letters.
Prior to fifteen years ago, astronomers never thought that the early Universe would have had massive galaxies. It had been conventionally regarded as a hotbed of star and galaxy formation, with the earliest galaxies relatively smaller than those that formed later. However, some began to theorize that galactic maturation may not occur at the same rate, and some might have gone through the process much faster. Karl Glazebrook, a co-author on the new paper, published results in 2004 of evidence of massive galaxies when the Universe was about 3 billion years old. This new study found evidence of massive galaxies that were mature in half of that time.
The team was comprised of astronomers from Macquarie University, Swinburne University of Technology, and the Australian Astronomical Observatory (AAO). The study involved analyzing data from the Magellan Baade Telescope’s FourStar camera, the Hubble Space Telescope’s Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey and Great Observatories Origins Deep Survey.
The galaxies themselves were very faint and had to be imaged in near-infrared wavelengths. The astronomers saw the galaxies as they were an average of 12 billion years ago, which made it very interesting when most of the light coming back was the traditional red which indicates that though the galaxies had 100 billion stars each, they weren’t forming any new stars. For massive galaxies at the dawn of the Universe, having so many mature stars was very uncharacteristic.
A region that has an exceptionally high rate of stellar formation is described as a “starburst.” The team believes the galaxy may have had something similar to a starburst phase which allowed these galaxies to form so much more quickly than the rest of the stars in the early Universe. There may have also been another influencing factor to force the galaxy to stop producing new stars.
In order to better understand how these galaxies formed and matured, the team will target galaxies that are more distant and thus, older. So far, the most distant galaxy known to astronomers is Abell2744 Y1, which was announced last month. It is approximately 13.2 billion years old.