M101 from AKARI
University of Tokyo used AKARI to observe M101, a spiral galaxy 170 thousand light years in diameter. AKARI's new observations reveal differing populations of stars spread across its spiral arms.
AKARI observed the galaxy at four infrared wavelengths (65, 90, 140, and 160 micrometres) using the Far-Infrared Surveyor (FIS) instrument. Many young high-temperature stars populate the spiral arms, revealing the areas of star formation and warming the interstellar dust. This causes the galaxy to shine at shorter infrared wavelengths. In contrast, the longer wavelengths show where the â€˜cold' dust is located. Normal stars, typically like our own Sun, warm this dust.
The image shows the distribution of cold (blue) and warm (red) dust overlaid on the visible (green, showing distribution of stars) and far-ultraviolet (cyan, indicating the location of young stars) images of M101.
The evidence points to M101 having experienced a close encounter with a companion galaxy in the past, dragging out gas from the hapless companion. The gas is now falling onto the outer edge of M101 at approximately 150 km/s, triggering the active star formation.