|What is this?||Cold clumps of dust detected by Planck|
|Where is it in the sky?||All over, though mainly in the Galactic Plane|
|How big is it?||The cores are clouds of dust, collapsing under gravity to eventually form one or more stars|
|How far away is it?||Some of the clumps are up to 12,000 lightyears away|
|What do the colours represent?||The redder sources are colder, while the brighter ones are warmer. The background image is the Planck first all-sky map.|
Many of the objects Planck sees as it scans the sky are compact clouds of dust within our own Galaxy, the Milky Way. There are over 10,000 in total, but the most reliably detected, numbering at 915, have been released in the Early Cold Core Catalogue. Some of them have been calculated to have incredibly low temperatures, below 10 K (-263oC), and these represent the initial stages of star formation, when a cloud of dust is starting to collapse under its own gravity. The dust is emitting submillimetre light, so the three highest frequencies of Planck are used for this.
As expected, many are located relatively close to the Sun, though some are up to 12,000 lightyears away. Most are in the plane of our Galaxy, but since Planck is observing the whole sky it can detect them above and below the main disc. “Thanks to Planck’s ability to measure extremely low temperatures with very high accuracy over the entire sky, we have been able to track down the distribution of the coldest dust on very large scales throughout the Milky Way,” comments Ludovic Montier from the Institut de Recherche en Astrophysique et Planétologie (IRAP) in Toulouse, France, who led the effort of compiling and analysing the sample.
“The majority of the cold material detected by Planck is either organised in filaments or located at the illuminated edges of pillars of dense gas,” notes Mika Juvela from the University of Helsinki, in Finland, who co-led the investigation along with Ludovic Montier. Many of them are aligned with regions where stars are already forming, supporting the theory that the formations of one group of stars can seed the formation of another.
The relatively low angular resolution of Planck doesn not allow it to peer into the clumps, which is where Herschel comes in. “Thanks to Herschel’s higher resolution, we have been able to peer deeply into the clumps detected by Planck and to scrutinise their detailed structure,” explained Isabelle Ristorcelli, also from the Institut de Recherche en Astrophysique et Planétologie (IRAP), who led the study along with Mika Juvela, University of Helsinki.
Studying the emission from cold dust in our own Galaxy is also of enormous importance to understand the behaviour of dust and the overall star formation processes in other galaxies. “The data gathered within the Milky Way represent a local guidebook to interpret what we see, with much less detail, in galaxies outside our own,” explains Dave Clements from Imperial College London, who guided a study based on Planck observations of almost 500 nearby galaxieswithin a few billion lightyears. “Understanding the role of cold dust in the local galaxy population is, in turn, extremely useful to calibrate observations of galaxies at much higher redshift, such as those that are currently being performed with Herschel. Together, these two ESA missions will allow us to build a ladder connecting our Milky Way to the faint and distant galaxies and uncovering the evolution of dusty, star forming galaxies throughout cosmic history,” he adds.
This is one of a number of early Planck results based on scientific papers published in early 2011.
This movie shows some examples of the cores seen by Planck, with higher resolution images from Herschel.