According to an August 15 news release from the European Space Agency’s Hubble Information Centre, the Hubble Space Telescope is the world’s key spacecraft for exploring the birth of modern galaxies. To accomplish this, the Hubble Sequence classifies galaxies according to their structure and star-forming action, organizing them into a wide array of spiral, elliptical, and irregular shapes with whirling arms, nebulous halos and brilliant inner bulges. Two main types of galaxy are identified in Hubble Sequence: elliptical and spiral. An ancillary type, known as lenticular, settles somewhere between the two main galaxy types.
According to BoMee Lee of the University of Massachusetts and lead author of a new paper exploring the Hubble Sequence, when it comes to studying the structures of ancient galaxies, “…[Y]ou need to peer at distant galaxies and compare them to their closer relatives, to see if they too can be described in the same way.” (The paper, entitled “CANDELS: The correlation between galaxy morphology and star formation activity at z ~ 2,” is set to appear in the Astrophysical Journal.)
So, the team of astronomers used the Hubble Space Telescope to peer 11 billion years into the past, to study the structure of distant galaxies. This observation allowed scientists to stretch beyond the 8 billion years that the Hubble Sequence covers, and opens up 80 percent of the Universe’s history. The scientists found that, after observing galaxies 11 billion years in the past, they do indeed fit into the Hubble Sequence classifications.
This sentiment was echoed by study co-author Arjen van der Wel of the Max Planck Institute for Astronomy in Heidelberg, Germany, who said, “This is the only comprehensive study to date of the visual appearance of the large, massive galaxies that existed so far back in time. The galaxies look remarkably mature, which is not predicted by galaxy formation models to be the case that early on in the history of the Universe.”
According to Lee, “The huge CANDELS [Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey] dataset was a great resource for us to use in order to consistently study ancient galaxies in the early Universe. And the resolution and sensitivity of Hubble’s WFC [Wide Field Camera] 3 is second to none in the infrared wavelengths needed to carry out this study. The Hubble Sequence underpins a lot of what we know about how galaxies form and evolve — finding it to be in place this far back is a significant discovery.”