There are quite a few mysteries in astronomy; things we don't understand. The vast majority of them are smallish in scope, things that can probably be solved with a little more work, more observations. These are more like questions than outright mysteries; things we just don't have the answers to quite yet.
But then there are some that really are mysteries: unexpected oddities that, for now, defy explanation. One of these reared its head again recently, when observations by the ground-based Subaru and Keck observatories were combined with those from the space-based telescopes Hubble and Spitzer. It doesn't look like much of a mystery -- just a red smudge -- but it pushes the boundaries of what we think the very Universe itself can do.
[Click to enbigbangenate.]
First, holy cow, what an image! Incredibly, nearly every single object in that picture is an entire galaxy, a vast collection of billions of stars. They're also very distant; I doubt any of the bigger ones are closer than several billion light years away.
And lurking off to the side, where you'd hardly notice it, is that little red guy. Named GN-108036, it's at the soul-crushing distance of 12.9 billion light years away. That means that the light we see here left that galaxy when the Universe was only a few hundred million years old.
As you might imagine, it may look faint, but at that distance it's remarkable we can see it at all. But we do, because it's amazingly luminous, perhaps the most intrinsically bright galaxy seen at that distance ever found. Of course, we don't see too many galaxies farther away than this! And that's part of the mystery.
As the Big Bang model of the cosmos goes, the Universe began 13.73 (+/- .12) billion years ago. It was very hot, and started cooling as it expanded. It took quite a bit of time before local pockets of gravity could overcome this ferocious heat, and the first stars and galaxies could form, something like 400 million years after the Bang itself.
So when we look at these very distant galaxies, we're seeing them as they were not long after they formed. At some point, if you look back far enough, you just don't see many galaxies. Either they haven't formed yet, or they are too faint to be seen at that great distance.
But GN-108036 is there. Apparently, the reason it's so bright is that it is cranking out stars; it looks like that red smear (at the time this light left it) is making as much as 100 solar masses worth of stars every year! That's a lot. Our Milky Way is 100 times the mass of GN-108036, but this small, distant, young blob is churning out stars at a rate dozens of times faster than we are.
Why? That's not clear. Conditions in the early Universe were different than they are now, with lots more gas available to make stars. But only a handful of galaxies (literally, fewer than a dozen) are known at this tremendous distance, so a lot of the details of how they behave are unknown. GN-108036 is far and away brighter than the others known, so that makes it even more mysterious. But it's adding stars to its stockpile very rapidly, and may be the precursor of the giant galaxies -- like our own -- that we see today.
Even with the amazing arsenal of telescopes we have today, with state of the art detectors, this galaxy is on the thin hairy edge of what we can detect. The Universe is rich and thick with mysteries, and the beauty of it is, the harder we push the boundaries, the more weirdness we find. But -- and this is a big but -- the Universe obeys its own rules. Those rules are the rules of science, which is no coincidence; science was developed as a way of understanding nature. We may have a hard time understanding what we're seeing at first, but the most amazing thing about the Universe may be that it's knowable. What are mysteries today will be understood tomorrow, and new mysteries will be waiting for us then.