Astronomers working with Fermi -- a mission that is mapping the sky in gamma rays -- have just released a new catalog of objects detected by the spacecraft. They've re-analyzed two years worth of data and have found nearly 2000 objects blasting out this super-high-energy form of light.
[Click to enhulkenate, and see a labeled version.]
The map is set up in galactic coordinates, so the Milky Way itself runs across the center. There are a lot of gamma-ray sources in our galaxy, most of which are bright simply because they're close. Others are actually luminous sources like the Crab Nebula, various pulsars, and other violent objects. The map is very similar to one released by Fermi a while back, but this new one is more sensitive, and can see fainter objects.
About half the detected sources are active galaxies: distant galaxies with supermassive black holes at their hearts, actively gobbling down matter and spewing out vast amounts of energy in the process (black holes are sloppy eaters). The folks at Goddard Space Flight Center put out a nice, short video explaining this:
[High-res versions of the video are online.]
What's even cooler is that for a lot of these sources, maybe half, we don't know what the heck they are. We haven't detected optical counterparts (or at some other part of the spectrum,) that lets us more easily identify them. They may be dust-enshrouded galaxies, or sources inside our galaxy, or something in between. The only way to know is to keep observing them with Fermi, and try with different telescopes too.
I worked on the education and public outreach on Fermi before it launched (when it was still called GLAST, as it always will be in my heart). I'm glad to see it still pumping out the science, and teaching us about the Universe. And the best part, of course, is the mystery it's showing us. Gamma-ray astronomy only began a few decades ago and we've learned a huge amount, but we still have a long way to go.