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This is the story of an unusual galaxy. Stick with me...
Light takes time to travel, so in a way, your eyes are a time machine.
The sunlight you see actually left the sun eight minutes ago.
It takes 100,000 years for light to travel across our Milky Way galaxy, an island of several hundred billion stars, including our sun. The light from the farthest star you can actually see using just your eyes began its journey across space when the first humans settled in North America.
But the farthest object your unaided eyes can see is Andromeda; another galaxy like our own. It's about 2.5 million light years away, across empty space; we see it as it was just before the earliest humans evolved.
Using astronomical data, the map of the visible universe shows these galaxies to be part of an unfathomably large, three-dimensional webbed filigree of hundreds of billions of galaxies, carved out as material was pulled together by gravity, after the Big Bang.
(In this amazing video about the power of 10, we get a glimpse, at around 4:17, of the intricate structure of the universe, where each point of light is not a star, but a galaxy.)
How do we test our understanding of galaxy formation?
We have hypotheses and theories as to how we think galaxies evolve, and we run computer simulations and are able to create a lot of the structure we see in the observable universe.
That's Dr. Patrick Treuthardt, Assistant Head of the Astronomy & Astrophysics Research Laboratory at the North Carolina Museum of Natural Sciences. He collaborated with a team from the University of Minnesota on the discovery and description of an extremely rare object known as a “Hoag-type galaxy” because it has a central bulge with a ring around it, like a similar galaxy discovered in 1950.
This object, unofficially called Burcin's Galaxy after discoverer and lead author Dr. Burcin Mutlu-Pakdil, is about 360 million light years away. We see it as it looked around the time our ancestors were crawling out of the ocean.
What we ended up doing is subtracting out the bulge, subtracting out the center of that galaxy, the light from the center, and what we were able to find was a diffuse red ring, underneath the bulge light. This is what makes it unique, in that it's a Hoag-type object, but it actually has two rings instead of one.
Hoag objects make up less than 0.1% of all known galaxies, and this one with two rings might be a one-of-a-kind discovery.
So, what's so important about the ring colors?
Blue regions in a galaxy are generally regions where stars are being formed. These are new stars. But the thing is, the more massive the star is, the more quickly it burns out. So it's just like if you have an SUV vs. a motorcycle. The SUV is going to burn through gas faster because it's a more massive object than, for instance, a motorcycle, which is less massive and it won't burn through its fuel as fast. The same thing happens with stars. So, these really massive stars are blue, and they'll burn out quickly, and you'll just be left with these lower mass red stars. So, for instance, in our galaxy there's a bright blue ring surrounding this yellow-orange central region, the bright blue ring is all these really massive stars that will burn out quickly. So this is actually a somewhat new feature. And when you look at the yellowish-orange center to it, that's actually all the old stars, and all of the blue stars have burned out, so you're left with these older features in there. And so, that red ring is probably a really old feature, where all the blue stars have since burned out, and we're just left with the red stars leftover.
What we think might have happened is that, sometimes there's gas between galaxies, and maybe there happened to be a dense region of gas that came by and basically fell on the galaxy forming at least one of these rings. Or it could be a smaller galaxy came by and maybe got shredded in the gravity of this galaxy. But we're not entirely sure about what's going on with this galaxy, so we actually need more data to figure that out.
A discovery like this can help us better understand the universe.
When we run across these unusual objects, our theories may break down; so something's going on where we're not accounting for some of these unusual objects. So there's probably some tweaking we need to do in understanding the evolution of galaxies.
Science is a process. Science is always testing its ideas. Nothing is 100% all the time in science. Everything can be tested, and it should be tested. Any time we find something new and we use our current theories to explain it, if it holds, then that's good. If it doesn't, then we need to modify our theories. It may be a drastic overhaul or it may just be a small tweak. And so basically that's all science is, is you take things that explain things very well, and you just build on top of it.