The central region of the Milky Way

There is so much obscuring dust between us and this region that visible light is extinguished by factors of over a trillion. Infrared, radio and some X-ray radiation, however, can penetrate the veil, and they have allowed astronomers to develop the picture just outlined. One span of the spectrum of particular interest to astronomers is the four octaves of infrared light from the short infrared band (just adjacent to the visible) to the submillimeter. It is precisely in this span that a large fraction of the universe emits most of its radiation – the reason being that ubiquitous, cool dust absorbs starlight (and many other kinds of radiation) from sources and re-radiates it here, in this far-infrared band. The Herschel Space Telescope, launched last year, is a facility able to detect this light.

CfA astronomers Mireya Extaluze, Howard Smith, Volker Tolls, Tony Stark, and Eduardo Gonzalez-Alfonso have used newly archived data from Herschel surveys of the region to publish the first complete far-infrared picture of the inner galaxy. The images reveal arcs, star clusters, and clumps of material, most of them previously known from radio observations, but all now seen in emission in the light of the cool dust they contain. The astronomers model the dust emission, and find that previous observations had been unable to sense a cold but massive component whose temperature is only about 23 degrees above absolute zero. The team also finds that the character of the dust emission varies across the region, and that the total radiant output of the inner donut region alone is two million solar-luminosities. These results mark the beginning, not the end, of a detailed analysis of the various cool, dusty structures found near our galaxy's core.

Provided by Harvard-Smithsonian Center for Astrophysics