Space is black. I mean, duh, right? But really, it’s black because it’s almost entirely empty, so even with stars scattered around, there’s nothing to light up.
But some parts of space are bright: clouds of gas can be lit up by nearby stars, making them glow. However, just to make things more fun, there can be thicker patches of dust mixed in that block the light from the stars and gas behind them. We see lots of those, they’re pretty common. But there’s yet another "however": that dust only blocks the visible light. In the infrared, that dust should itself glow because it’s warm.
NGC 1999 — seen here in a famous Hubble picture — has all these ingredients. It’s a thick region of gas and dust. Stars are being born in and around it, brightening it with their reflected light (as seen in the image; the star V380 Orionis on the left is lighting up the surrounding space junk) as well as warming it up and making it glow on its own. Even so, the oddly-shaped patch to the right was thought to be an unusually dense blob of dust, blocking the light from gas on the other side of it from us.
A lot of the time those dense spots are where stars are being born, and the only way to see them is in the infrared. So astronomers pointed the European space-based Herschel infrared observatory at it, fully expecting to see the whole thing glowing with perhaps a nascent star forming in the dark blob. But that’s not quite how it worked out…