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Unveiling new Galactic surprises

15 February 2012

Unveiling new Galactic surprises webThe “Galactic Haze” as measured by Planck, seen as a glow near the Galactic Centre. The dark band across the middle is where strong emission from the rest of the Galaxy has been blanked out. The origin of the Haze is not yet known, though there are a number of possibilities. Image credit: ESA/Planck collaboration.

The European Space Agency’s Planck mission with the support of University astronomers has unveiled more surprises about our Galaxy, bringing scientists closer to being able to understand the structure of the Universe.

The results include previously unknown clouds of cold gas, and a mysterious haze of microwave emission near the centre of the Galaxy.

Planck is surveying the sky at microwave wavelengths, with a primary science goal of observing the Cosmic Microwave Background - the afterglow of the Big Bang. But in the course of its cosmological quest Planck is also making maps of anything in the foreground, which includes our own Galaxy.

Astronomers from around the world including those from the University’s School of Physics and Astronomy are busily pouring over these maps, with some of the intermediate results being presented for the first time.

Most of the emission from our Galaxy is due to hot gas and dust between the stars, or from very energetic electrons moving through magnetic fields. Planck’s instruments are also able to pick up the emission from very cold clouds of gas scattered throughout the Milky Way.

The main constituent of these clouds is hydrogen, though this is very difficult to observe as hydrogen molecules do not emit much light. Instead, astronomers identify the gas clouds by detecting emission from carbon monoxide molecules, which although rarer is much easier to detect.

"It is great that such data comes serendipitously through the course of getting to the principal Planck science results," said Dr Locke Spencer, School of Physics and Astronomy, and member of the Planck collaboration.

"Observations of carbon monoxide at these wavelengths are very challenging to obtain, and require many experts of different specialities working together. The full-sky map of carbon monoxide will provide a vital resource for astronomers using other telescopes, pointing out new places to look for stars in the process of forming," he added.

An even more unusual result is the detection of a mysterious haze of microwave emission near the Galactic centre. A relatively well understood phenomenon, called ‘synchrotron emission’, involves very fast electrons travelling through magnetic fields. The haze, however, seems to be caused by an unexpectedly energetic population of electrons, the origin of which is uncertain.

There are a number of possible explanations for the haze, though none have been confirmed. It could be that there are more supernovae occurring in the centre of the Galaxy than previously thought, or that the flow of material from the Galactic centre is stronger for some reason.

A more intriguing possibility is that the electrons could be the result of the annihilation of dark matter particles. If true, this would provide a new way for tracing this unusual constituent of the Universe.

"We always knew that with all sky coverage in nine wavebands we would make unexpected discoveries," said Professor Peter Ade, School of Physics and Astronomy, who has been responsible for building, testing and calibrating the ultra-cold sensitive detectors at the heart of the High Frequency Instrument.

"The detection of the galactic centre haze and the serendipitous mapping of cold gas are good examples of this. As we continue to dig deeper into the images and results we should expect many more fascinating discoveries," he adds.

Related Links

School of Physics and Astronomy

Planck

European Space Agency (ESA)