Infrared Dark Clouds in the Milky Way

Typically if an astronomer wants to see into or through a thick dark cloud in space, they will use an infrared-sensing telescope. However, in this infrared image from NASA's Wide-field Infrared Survey Explorer, or WISE, there are some clouds that are so cool and thick that even infrared light coming from within or the background can't penetrate them. The black areas in this image -- called infrared dark clouds -- are exceptionally cold, dense cloud cores seen in silhouette against the bright diffuse infrared glow of the plane of the Milky Way galaxy. The clouds are a great example of why it is so useful for astronomers to be able to observe in many different wavelengths of light.

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.

However, the darkest areas here are places where the cloud is extremely compact and chilly, so much so that it is opaque even in the infrared wavelengths that WISE sees. To see them glow, one would need to look in even longer wavelengths, for example those detected by the European Space Agency's Herschel mission, which has important NASA contributions

These dark clouds are so dense that if you were located in the middle of one of them, you wouldn't be able to see anything -- no stars, no galaxies, only darkness. This dense material will eventually result in the formation of new stars and planets.

This image was made from observations by all four infrared detectors aboard WISE. Blue and cyan (blue-green) represent infrared light at wavelengths of 3.4 and 4.6 microns, which is primarily light from stars. Green and red represent light at 12 and 22 microns, which is primarily light from warm dust.

Photo credit: NASA/JPL-Caltech/UCLA

Cold Cores in the Milky Way

This map illustrates the numerous star-forming clouds, called cold cores, that Planck observed throughout our Milky Way galaxy. Planck, a European Space Agency mission with significant NASA participation, detected around 10,000 of these cores, thousands of which had never been seen before. Cold cores are chilly chambers of gas and dust where stellar embryos are just beginning to take shape. Some of the cold cores found by Planck are the coldest ever observed, as cold as just seven degrees above absolute zero, or minus 447 degrees Fahrenheit.

The blue data show the density of the cores, some of which are shaped more like clumps or filaments than spherical cores. Other missions, like the Herschel Space Observatory, can follow-up on the Planck discoveries, and see the structures in more detail.

Planck is an all-sky survey mission, scanning the sky at longer wavelengths of light, ranging from infrared to radio waves. Its ultimate goal is to measure the cosmic microwave background -- ancient radiation from the Big Bang that created our universe 13.7 billion years ago. But in the process of making these precise measurements, Planck is catching objects that lie in front of the cosmic microwave background -- objects like cold cores in our galaxy, in addition to distant galaxies.

About 1,000 of the cold cores observed by Planck are being released to the public January 11, 2011, in the mission's "Early Release Compact Source Catalogue." These are the best sources of the bunch, and the coldest.

Photo credit: ESA/NASA/JPL-Caltech