Pictures like this one always fascinate me. Astronomy gives us a chance to look at the universe in amazing and different ways. The most obvious is that we just get to look at pretty stuff. But, after you gaze for a while, you start to ask questions. They start out as small ones, like, “What am I seeing?” and “How far away is it?”
To answer those seemingly easy questions requires a lot of information. And getting that information is what makes astronomy so fascinating. The picture above is a gold mine of information. So, let’s start with “what am I seeing?”
Well, you’re seeing a field of the sky that is chock full of distant galaxies. Hubble Space Telescope looked at this area of the sky for a good long time, seeing more and more faint objects the longer it looked. This makes sense, since the longer it looked, the more light it could gather. The more light you gather from dim, distant objects, the easier it is to eventually see them. To see something a long ways away, you have to look for a long time.
The result of all this HST-type staring was an image called the “Hubble Ultra Deep Field.” The “deep” part means it shows stuff that is deep in space, farther away. And, as we are all taught in our first astronomy classes, farther away in space means “further back in time.” So, the Hubble Ultra-Deep Field (which I’ll now refer to as HUDF) is showing us galaxies as they looked when the universe was a mere baby, about 12 billion years ago.
Now, the interesting thing is that this image answered both questions at once. We now they’re galaxies in that image, and we know that they’re galaxies as they appeared in their youth, back when the first galaxies were being formed. That leads us to another question: “What happened in those baby galaxies ‘way back in the day?”
This is where the Spitzer Space Telescope comes in. It’s sensitive to infrared light. Are those galaxies giving off infrared light? Well, probably they were, but what Spitzer is really seeing is something a little more complex than the IR that’s given off by stuff like warm dust in between the stars.
Think of it this way: galaxies, even back then, can be hotbeds of star formation. And the births of stars gives off a lot of really hot radiation in the form of ultraviolet and other wavelengths of energetic light. Spitzer as well as Hubble zeroed in on one particular galaxy in the field to study its star-formation rate. They expected it to be active in creating new stars. Imagine their surprise when they found out it was bigger and much more mature (in terms of star formation)!
How did they know this galaxy was older than expected? Bigger, more mature stars give off infrared radiation that Spitzer’s ultra-sensitive detectors can “see.” Also, and this is very cool, the telescope saw wavelengths of light that indicate something really energetic is happening in the core of this very distant galaxy: a black hole is stirring things up and creating a lot of ruckus!
Now, to understand this last bit, it’s important to know that early galaxies should show at least some hot, young stars, and that black holes at the centers of galaxies are hallmarks of more mature galaxies. At the period of cosmic history that this galaxy existed, astronomers didn’t expect to see such a mature one with lots of hot, massive stars, and a black hole at its heart. So, this galaxy and its bulked-up form adds another piece to the puzzle of how galaxies were built and developed in the early universe.
Astronomers think most galaxies were built up through mergers of smaller galaxies. However, the discovery of this object means that at least a few galaxies formed quickly back in the early days, and were more complete earlier in history. It would have been a terrifically energetic explosion of starbirth that created this husky “teenage” galaxy way back then. The very quick births of huge stars in this galaxy could have helped reheat the universe very shortly after it cooled following the Big Bang.
See what you find out when you look at a picture and ask a few simple questions?