Planck Stares Through Our Dusty Milky Way
This week, the European Space Agency announced the first science results from Planck, a highly anticipated space-born millimeter and sub-millimeter wavelength telescope.
Though Planck’s primary mission is to study the Cosmic Microwave Background (CMB), the mission is already allowing astronomers to do science on our Galaxy, star-forming galaxies, and massive galaxy clusters along they way.
The CMB is the “glow” emitted all over the universe just 380,000 years after the Big Bang. By studying the tiny fluctuations in this background with unprecedented resolution, Planck will aide astronomers in filling in some important cosmological details, such as how the early inflation epoch may have occurred, or whether there were primordial gravitational waves.
In order to study the background in that much detail, however, the mission scientists needs to learn as much as they can about all the sources in the foreground in order to properly remove them from the CMB picture. As I sometimes say, one astronomer’s noise is another astronomer’s data, so science can be done on these foregrounds as they are carefully characterized.
For example, some of the foreground sources appear to be dust-shrouded galaxies with prodigious star forming rates, 10 to 1000 times that of our galaxy. The obscuring dust blocks visible and shorter wave infrared light from reaching us, but re-radiates that energy in the sub-mm and mm regime, making them visible to Planck. Also visible as “holes” in the microwave background are galaxy clusters, using the Sunyaev-Zel’dovich effect, which can shed light on the largest scale structure, and thus history, of the universe.
Also crucial to Planck’s calibration is identification of a microwave “fog” that appears to be centered around he dustiest parts of our own galaxy. This “anomalous microwave emission” was indeed traced to very rapidly spinning dust grains. They have a very small dipole moment and spin so quickly due to interactions with fast-moving atoms or ultraviolet photons. Planck’s wide wavelength range made this identification possible, as shown in the composite image above.
Though it will be two more years before the CMB science is analyzed and announced by Planck scientists, there is already a wealth of information about the cold and dusty universe to keep astronomers busy for quite a while. Who knew dust could be so interesting?!
Images: Top – From the animation of the sources from the Early Release Compact Source Catalog. Credit – ESA/Planck Collaboration. Middle – Composite image of the Rho Ophiuchus molecular cloud, one location of the anomalous microwave emission. Credit – Haslam et al. (1982), ESA/Planck Collaboration