Today, social media users might have seen that the Hubble Space Telescope’s new image of galaxy UGC 4879, a small galaxy in the Ursa Major constellation, is among the many things trending. At first glance, it’s just a blob of stars, like billions of other blobs of stars in the universe. Hubble takes hundreds of pictures of those. So what’s the big deal?
Well, the first thing that is a bit unusual about UGC 4879 (I think it needs a real name. Ralph, maybe?) is that it doesn’t have a shape like many other galaxies we’ve seen. Most of the galaxies we’re familiar with from pictures and books are spiral galaxies, like our own and our neighbor, the Andromeda galaxy, or are a more cohesive elliptical shape. UGC 4879, on the other hand, has a very loose, messier formation, which also makes it harder to see. There isn’t an ultra bright concentration of stars in its center. UGC 4879 is also a dwarf galaxy, very small compared to others. But these are not the most important unique things about this galaxy.
Possibly the most important thing about this galaxy is that it is isolated.
What does this mean? There are 2.3 million light years between UGC 4879 and its nearest neighbor, Leo A. This is about the same distance as between the Milky Way and Andromeda, which are both much larger in mass and density than UGC 4879. But because Leo A is also a dwarf galaxy that is similar in structure to UGC 4879, that means that these two galaxies do not interact with each other very much. I’m trying not to get into relativity and advanced physics very much here, but think of it this way: the more massive something in space is, the more of an effect it has on its neighbors. The Sun holds the planets in orbit around it. Its mass is great enough where it has that much of a gravitational pull on all the planets to keep them in line. The Earth is massive enough to keep the Moon in orbit, but it’s not a one-sided relationship. The Moon has a pull on the Earth as well; that’s what causes the tides in our oceans. Andromeda and the Milky Way are so massive that even across ~2.5 million light years, these galaxies interact with one another. They affect each other’s movements. But two dwarf galaxies like UGC 4879 and Leo A do not have enough mass to pull on each other very much. There is always some minuscule interaction—nothing exists in a vacuum, even in the deepest space except on a theoretical level, but this is as close as we get in astronomy to seeing how a galaxy behaves when its on its own.
And why would we want to see that? Well, galaxies are nothing but a collection of stars. It’s rather more complicated than that, because a galaxy can form from accretion, where several stars that are nearby are drawn in by the gravity of other stars and then stay together in a group. Eventually, these stars crash into each other, or they grow old and die, and in turn, new stars are born. This type of interaction is what astronomers are looking at in UCG 4879. Now, when galaxies are large enough or close enough to have a strong interaction with each other, the galactic gravitational pull has an effect on the star creation within the galaxies. Believe it or not, Andromeda, a galaxy we can just barely see with our naked eyes, has an effect on how the stars within our Milky Way move and behave, how the dust accretes in nebulae to form stars, etc. But in a remote, isolated galaxy like UGC 4879, the stars are only really, to a measurable degree, affected by the other stars in that galaxy.
Star formation in UGC 4879 has happened a bit differently than in the Milky Way and other galaxies we’ve studied, which suggests that perhaps being isolated has made a difference. In the first four billion years since the Big Bang, there was a lot of star birth, which is typical. But then there followed an odd nine billion year lull in star birth, which ended only fairly recently one billion years ago, when star genesis began again (we can tell the age of stars by the type of light they emit, as well as their masses and densities and other factors, and we can tell there wasn’t star genesis during this time because the relatively similar ages of the stars—lots of ten billion year old stars, no five billion year old ones, but then suddenly, more one billion year old ones, etc). There is a possibility (conjecture on my part, one of many theories--one of the hardest parts about studying astronomy is the sheer volume of things we just DON'T KNOW and can only theorize about) that this odd behavior is because there are fewer interactions causing collisions and other events that lead to the star birth that happens more or less all the time in other bigger galaxies. It’s interesting to study whether this is how a micro-universe would behave: lots of activity, then things calm down until star death causes more new stars to be born, or eventual, much slower collisions cause the same. Watching a small scale system like this can help us understand the behaviors of much larger scale things like other galaxies and even the universe, where there is just too much going on, too many interactions happening, to see cause and effect clearly.
UGC 4879 provides a great laboratory to observe a simpler version of the universe like this, proving once again that size isn’t everything.
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Melanie R. Meadors is the author of fantasy and science fiction stories where heroes don’t always carry swords and knights in shining armor often lose to nerds who study their weaknesses. She’s been known to befriend wandering garden gnomes, do battle with metal-eating squirrels, and has been called a superhero on more than one occasion. Her work has been published in several magazines, and she was a finalist in the 2014 Jim Baen Memorial Science Fiction Contest. Melanie is also a freelance author publicist and publicity/marketing coordinator for both Ragnarok Publications and Mechanical Muse, an independent gaming company. She blogs regularly for GeekMom and The Once and Future Podcast. Her short story “A Whole-Hearted Halfling” is in the anthology Champions of Aetaltis, available now on Amazon. Follow Melanie on Facebook and on Twitter as @MelanieRMeadors.