This image taken by NASA's Wise Satellite is in the infrared spectrum, meaning it can reveal the light that is normally hidden behind thick, dark clouds of gas. But some clouds are so dark that no light can get through.
These are known as infrared dark clouds — they're the black patches in the image above — and they're so cold and so dense that even our most powerful infrared telescopes cannot peer inside them. Visible light is unknown inside these gas clumps — if you were to take a starship inside one of these cosmic clouds, you wouldn't see any neighboring stars or galaxies or any other light at all. These clouds are places of quiet, constant blackness.
That said, the darkness is not eternal, and indeed these clouds eventually undergo about as dramatic a metamorphosis as one could imagine, as they give birth to new stars and planets. Until then, these clouds remain opaque to all but the longest wavelengths. Even the bright lights that surround these clouds are beyond our own familiar visible wavelengths, and that's why the infrared detectors on NASA's WISE telescope are so crucial.
Astronomers from the WISE mission explain what we're seeing here, and why we wouldn't see it otherwise:
If you were to look at this same region of the sky through a backyard telescope, you would see a sea of stars packed together, similar to the thousands of blue stars seen here. You might also notice small patches of darkness that appear to block out the stars behind them. But what you wouldn't see are these beautiful clouds colored green, yellow and red in this image from WISE. Those are only seen in infrared light. In fact, the places where you see dark patches with your eyes are often the places where WISE sees bright clouds with its infrared "eyes." This is because those clouds are dense enough to block visible light, but not dense enough to block longer wavelengths of infrared light that WISE detects. In addition, they are too cool to shine in visible light but still warm enough to glow brightly in infrared light.