Full sky map: Rings and loops in the stars

The European Space Agency (ESA) Planck satellite, launched in 2009 to study the ancient light of the Big Bang, has also given us maps of our own Galaxy, the Milky Way, in microwaves (radiation at cm- to mm-wavelengths). Microwaves are generated by electrons spiralling in the Galaxy's magnetic field at nearly the speed of light (the synchrotron process); by collisions in interstellar plasma, by thermal vibration of interstellar dust grains, and by "anomalous" microwave emission (AME), which may be from spinning dust grains.

The relative strength of these processes changes with wavelength, and are separated using multi-wavelength measurements from Planck, from NASA's WMAP satellite, and from ground-based radio telescopes, giving maps of each component.

The new maps show regions covering huge areas of our sky that produce AME; this process, only discovered in 1997, could account for a large amount of galactic microwave emission with a wavelength near 1 cm. One example where it is exceptionally bright is the 200 light year-wide dust ring around the Lambda Orionis nebula (the 'head' of the familiar Orion constellation). This is the first time the ring has been seen in this way.

A wide field map also shows synchrotron loops and spurs (where charged particles spiral around magnetic fields), including the huge Loop 1, discovered more than 50 years ago. Remarkably, astronomers are still very uncertain about its distance -- it could be anywhere between 400 and 25,000 light years away -- and though it covers around a third of the sky it is impossible to say exactly how big it is.

This research was supported by an ERC Starting (Consolidator) Grant (no. 307209) and STFC Consolidated Grant (no. ST/L000768/1).