Hubble Looks 11 Billion Years Back in Time to Explore Distant Galaxies

Hubble has taken a look back in time to catch a glimpse of how galaxies form. The instrument has examined the universe 11 billion years ago in order to explore the anatomy of distant galaxies, revealing a little bit more about these ancient systems.

Galaxies are usually classified according to their morphology and star-forming activity. There's a veritable zoo of spiral, elliptical and irregular shapes that possess whirling arms, fuzzy haloes and bright central bulges. The two main categories of galaxies, though, are elliptical or spiral. A third type of galaxy, called a lenticular galaxy, falls somewhere between the two.

In order to understand the morphology of ancient galaxies, the researchers pushed Hubble's capabilities. While the furthest back the instrument has gazed was once 8 billion years, the scientists pushed that back a further 2.5 billion years. This covered a huge 80 percent of the past history of the universe.

"This is the only comprehensive study to date of the visual appearance of the large, massive galaxies that existed so far back in time," said Arjen van der Wel, co-author of the new study, in a news release. 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."

So what do these galaxies look like exactly? They appear to be split between blue star-forming galaxies with a complex structure, including disks, bulges and messy clumps, and massive red galaxies that are no longer forming stars. These two types, though, are relatively rare in the ancient universe. This particular scarcity has prevented previous studies from being able to gather a large enough sample of mature galaxies to properly describe their characteristics. However, that's now all changed.

"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 discover," said BoMee Lee, one of the researchers, in a news release.

The findings are published in The Astrophysical Journal.