Galactic Centre: Arcs, Arches and Bubbles

Each year the US National Radio Astronomy Observatory (NRAO) organises a radio image contest to find the best images made with their radio telescopes; the Very Large Array, the Greenbank Telescope and the VLBA. The best of 2008 have been chosen and the overall winner is this nice image of the central parts of the Milky Way.

A 2 by 1 degree field of the Galactic Center (the plane of the galaxy is horizontal in this image) and the surrounding Central Molecular Zone CREDIT: NRAO/AUI, Adam Ginsburg and John Bally (Univ of Colorado - Boulder), Farhad Yusef-Zadeh (Northwestern), Bolocam Galactic Plane Survey team; GLIMPSE II team

The three colours in the image represent different parts of the electromagnetic spectrum and highlight different physics. The purple shows 20 cm emission observed by the VLA, the orange parts are 1.1 mm emission observed by the Caltech Submillimetre Observatory and the cyan shows infrared emission seen by the Spitzer Space Telescope. The 20 cm emission is due to electrons spiralling in magnetic fields and regions of ionised hydrogen (HII), the 1.1 mm emission shows cold dust, and the infrared shows stars, point sources and regions with polycyclic aromatic hydrocarbons (which are also found in grilled meat).

For context, the bright white area towards the right-hand side of the image is Sagittarius A (the Galactic Centre) but I find the purple ribbons to the left of that to be the most intriguing part of the image. These are the Galactic Centre Radio Arcs and are linked to the centre by filaments known as the Arches. Like iron fillings close to a bar magnet, they probably show hot plasma flowing along large scale magnetic field lines.