Star formation processes revealed by Planck
26 April 2010
Within the frequency range of Planck, the gas and dust between the stars dominates the emission. (Above) a region of low star formation in the Perseus constellation as seen with Planck; (below) an active star formation region in the Orion Nebula, as seen with Planck.
Image Credits: ESA, LFI and HFI Consortia
New images from the Planck space observatory reveal the gas and dust between the stars and isolate the physical processes at work in our Galaxy. The new images are an eye-catching by-product of a spacecraft designed to look back at the earliest light in the Universe.
Our Galaxy, the Milky Way, is home to billions of stars, laced through with clouds of gas and dust known as the interstellar medium. In visible light most of the newly born stars are hidden by clouds of tiny dust particles dispersed between the stars. When observed at much longer wavelengths, where the Cosmic Microwave Background can be seen, the picture is very different as clearly demonstrated in new images from ESA's Planck mission. The dust is no longer a dark shroud, but shines out in its own right, and new aspects of our Galaxy are revealed.
Probing the processes at play
At wavelengths where Planck's sensitive instruments observe, the Milky Way emits strongly over large areas of the sky. This emission arises primarily from four processes, each of which can be isolated using Planck. At the longest wavelengths, of about a centimetre, Planck maps the distribution of synchrotron emission due to high-speed electrons interacting with the magnetic fields of our Galaxy. At intermediate wavelengths of a few millimetres the emission is dominated by ionized gas being heated by newly formed stars. At the shortest wavelengths, of around a millimetre and below, Planck maps the distribution of interstellar dust, including the coldest compact regions in the final stages of collapse towards the formation of new stars.
Prof Richard Davis of the University of Manchester's Jodrell Bank Centre for Astrophysics says
"The real power of Planck is the combination of the High and Low Frequency Instruments which allow us, for the first time, to disentangle the three foregrounds. This is of interest in its own right but also enables us to see the Cosmic Microwave Background far more clearly"
Once formed, the new stars disperse the surrounding gas and dust, changing their own environment. A delicate balance between star formation and the dispersion of gas and dust regulates the number of stars that any given galaxy makes. Many physical processes influence this balance, including gravity, the heating and cooling of gas and dust, magnetic fields and more. As a result of this interplay, the material rearranges itself into 'phases' which coexist side-by-side. Some regions, known as 'molecular clouds', contain dense gas and dust, while others, referred to as 'cirrus', contain more diffuse material.
Investigating the properties of the different components in the interstellar medium requires data at a range of frequencies. Planck will advance this effort hugely because it provides, for the first time, data on all the main emission mechanisms in one go. Planck's wide wavelength coverage, which is required to study the Cosmic Microwave Background, proves also to be crucial for the study of the interstellar medium.
Mapping the sites of star formation
The power of multi-frequency observations to discern the processes at play during star formation is beautifully demonstrated by these new Planck images. This first sequence, shown below, shows the interstellar medium in a region of the Orion Nebula where stars are actively forming in large numbers.
Peter Ade, of Cardiff University and co-Investigator on Planck, said:
"the power of Planck's very wide wavelength coverage is immediately apparent in these images. The red loop seen here is Barnard's Loop, and the fact that it is visible at longer wavelengths tells us that it is emitted by hot electrons, and not by interstellar dust. The ability to separate the different emission mechanisms is key for Planck's primary mission"
A comparable sequence of images, showing a region where fewer stars are forming near the constellation of Perseus, illustrates how the structure and distribution of the interstellar medium can be distilled from the images obtained with Planck.
Higher resolution versions of the images, along with a number of others, can be found at the UK Planck website.
Image Credits: ESA, LFI and HFI Consortia
A lucrative by-product for a ground-breaking mission
Precise measurements of the Cosmic Microwave Background are crucial to cosmology, and will improve our understanding of how our Universe formed and evolved. Planck will measure the Cosmic Microwave Background at the highest-sensitivity (a few parts per million), and resolution (5 arcminutes) over the whole sky. Doing so requires the removal of the 'foreground' emission arising from the Milky Way. The information gleaned during this process is providing, as a by-product, a unique view of the processes that led to the formation of the stars in the galaxies that populate our Universe. Since Planck will observe the Cosmic Microwave Background over the whole sky, it can also map large regions of the Galaxy. The image below shows the Orion region (on the left) and the Perseus region (on the right) overlaid on a picture of the sky at visible and infrared wavelengths.
Dr Clive Dickinson, also of the University of Manchester, commented that
"The Planck maps are really fantastic to look at. These are exciting times."
Planck maps the sky in nine frequencies using two state-of-the-art instruments, designed to produce high-sensitivity, multi-frequency measurements of the diffuse sky radiation: the High Frequency Instrument (HFI) includes the frequency bands 100-857 GHz, and the Low Frequency Instrument (LFI) includes the frequency bands 30-70 GHz.
The first Planck all-sky survey began in August 2009 and is close to complete (as of mid-April 2010). Because of the way Planck surveys the sky, the last bit of the first scan will be completed by late-May 2010. Planck will gather data until the end of 2012, during which time it will complete four sky scans. A first batch of astronomy data, called the Early Release Compact Source Catalogue, is scheduled for release in January 2011. To arrive at the main cosmology results will require about two years of data processing and analysis. The first set of processed data will be made available to the worldwide scientific community towards the end of 2012.
UK role in Planck
A number of UK institutes and companies form part of the consortium building the two focal plane instruments, HFI (High Frequency Instrument) and LFI (Low Frequency Instrument). The Jodrell Bank Observatory at The University of Manchester has produced critical elements of the LFI receiver modules. Cardiff University, STFC RAL and SEA have been involved with hardware development for HFI, while various UK research groups including Imperial College London and University of Cambridge form the London Planck Analysis Centre and Cambridge Planck Analysis Centre. These groups are involved with data analysis and simulation for the HFI data analysis and simulation software. More information can be found in the Planck briefing document.
Jodrell Bank's role in Planck
Jodrell Bank Centre for Astrophysics (JBCA) is directly involved with the two lowest frequencies of the Low Frequency Instrument, the 30 and 44 GHz radiometers. These have 4 and 6 detectors respectively, operating at 20K (-253.15°C or -423.67°F). The resolution on the sky will be 33 and 23 arc minutes, and the sensitivity 1.6 and 2.4 micro K (1s, over 12 months). The cryogenic low noise amplifiers which are the heart of the radiometers were developed at Jodrell Bank, with help from the University of Birmingham and The Rutherford Appleton Laboratory.
Dr B. Maffei and Dr G. Pisano are involved in the other focal instrument, HFI. First at Cardiff University and now at the University of Manchester, they have played a major role in the design, development and calibration of the Focal Plane Unit, in particular the cold optics, in collaboration with the Institut d'Astrophysique Spatiale - France, Maynooth University - Ireland and JPL/Caltech - USA.
For more information please contact
Dr Chris North,
School of Physics and Astronomy,
Cardiff CF42 3AA
+44 (0)129 208 70537
Dr Stuart Lowe,
Jodrell Bank Centre for Astrophysics,
Alan Turing Building,
The University of Manchester,
Manchester M13 9PL
+44 (0)161 275 4142.
Jan Tauber, Planck Project Scientist
Research and Scientific Support Department,
Directorate of Science and Robotic Exploration
European Space Agency