The Hubble Space Telescope has captured a rather striking image of a nearby galaxy, just 39 million light-years away, with an unusually youthful appearance that has left astronomers scratching their heads. Galaxies in our cosmic neighborhood tend to be elderly, and astronomers usually have to peep very far back in time to observe galactic evolution in the early universe. So is this glistening sprawl of stars and gas truly an exception, or is it deceiving us?
Galaxies are usually not very good at hiding their age; older galaxies are generally larger as they’ve collided and merged with other galaxies throughout their lifetimes, plumping them out. They’re also usually packed with various different types of stars—big ones, small ones, old ones and young ones. The fiery cores of stars also help to enrich older galaxies with heavy elements, as do various stellar events that occur over their lifetimes. Younger galaxies, on the other hand, tend to be small in comparison and have a similar chemical makeup to the primordial matter created in the Big Bang (hydrogen, helium and lithium).
Astronomers know this because they’ve been studying galactic evolution for years with the help of powerful telescopes, such as the NASA/ESA Hubble Space Telescope. These instruments allow us to gaze over phenomenal distances and because some of the light has taken billions of years to reach us, we are essentially peering back in time.
As we look further into the distance, and hence further back in time, we observe younger and younger galaxies. This is very useful for understanding how galaxies change over time, but unfortunately it can also be problematic. This is because baby galaxies are generally very faint and small. Those residing closer to us, on the other hand, tend to be more mature.
DDO 68, or UGC 5340, seems to be an exception to the rule. Just 39 million light-years away from us, this curious galaxy seems to be one of the best candidates discovered so far of a nearby young galaxy. 39 million-light years is obviously still an incredible distance, but young galaxies are usually substantially further from us, billions of light-years away.
Looking at DDO 68’s structure, appearance and chemical make-up, it seems to be pretty young. For example, it is lacking in heavy elements that would indicate previous generations of stars that lace the galaxy with more and more metals as they come to an end. Furthermore, the stellar population of this galaxy was thought to only be around 1 billion years old; much younger than our 5-billion-year-old sun.
Researchers will continue to study the Hubble observations to see if there are older stars in the galaxy, such as red giants, which currently seems to be the case. If this is true, then we know this galaxy is not only filled with infant stars and is therefore older than it gives away. If not, then this galaxy really is unique.