A galaxy recently imaged by the Hubble Space Telescope looks relatively young, but new analysis of those images shows that it may be older than it seems.
Astronomers were excited when Hubble first spotted the galaxy, dubbed DDO 68, because we hadn't yet seen a galaxy this close (only about 39 million light years away) that was potentially this young.
Young galaxies are important to astronomers because they help us understand how galaxies form and evolve, especially considering that galaxies evolve over billions of years. Thanks to telescopes like Hubble, we now have a way to watch these galaxies in their infancy, but usually, the younger galaxies are much farther away than DDO 68, which means they appear smaller in images.
On the other hand, galaxies that are closer are larger in images, and those images allow us to see details we might otherwise miss. Unfortunately, most of the galaxies close to our own are old ones.
So how do we know how old a galaxy is? Astronomers look for specific things, particularly at a galaxy's structure, appearance and composition. For example, older galaxies are usually larger because they have histories of collisions with other galaxies. The chemical composition of older and younger galaxies is also different. Newer galaxies contain more hydrogen, helium and lithium. Older galaxies are heavy in metals, created by multiple generations of heat created by stars.
At first glance, DDO 68, looks young, at least according to its appearance, its structure and its composition. It has less heavy elements, such as metals, associated with older galaxies. Astronomers also studied the stars of DDO 68, estimating that most were only about 1 billion years old. This might seem ancient, but in comparison, our Sun is about 5 billion years old.
"All of the available data are consistent with the fact that DDO 68 is a very rare candidate for young galaxies." says S. A. Pustilnik. "The bulk of its stars were formed during the recent merger of two very gas-rich disks."
However, new analysis of the images of DDO8 revealed giant red stars. This suggests that the galaxy has stars that are much older. If it has stars that are older, it is likely that the galaxy itself is older than it appears.
Astronomers hope more complex models will shed light on this galaxy's age, but regardless, the image captured of it by Hubble is beautiful.
