Hubble Explores Origins Of Galaxies
August 15, 2013

Hubble Helps Understand Origins Of Galaxies

John P. Millis, PhD for - Your Universe Online

One of the major astronomical advancements of the 20th century was the ability to study in great detail the galaxies that make up our Universe. Instruments like the Hubble Space Telescope (HST) have brought a level of resolution that has allowed us to trace the history and evolution of galactic dynamics.

Currently, galaxies are classified by the Hubble Sequence – a system whereby galaxies are grouped by their sizes, shapes, star types, and other factors. A deeper question, however, is at what point did galaxies begin to separate into these different classes?

"This is a key question: when and over what timescale did the Hubble Sequence form?" says BoMee Lee of the University of Massachusetts, and lead author of a new paper exploring the sequence. "To do this you 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."

To explore this question, a team of astronomers used the HST to peer back more than 11 billion years into the past, when the Universe was still very young. This is significant, because the Universe had only been shown to exhibit the Hubble Sequence characteristics back as far as 8 billion years; prior to this it was not clear whether the galaxy grouping characteristics would hold.

"This is the only comprehensive study to date of the visual appearance of the large, massive galaxies that existed so far back in time," says co-author Arjen van der Wel of the Max Planck Institute for Astronomy in Heidelberg, Germany. "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."

Older young galaxies, as those at such distances, are generally much smaller than the Milky Way, making their characteristics difficult to quantify. So researchers used a HST survey known as CANDELS which provided a large enough sample size of this small, young galaxies in the early Universe to begin grouping them together.

"The huge CANDELS dataset was a great resource for us to use in order to consistently study ancient galaxies in the early Universe," concludes Lee. "And the resolution and sensitivity of Hubble's WFC3 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."