While Messier 106 is regarded as a spiral galaxy, much like the Milky Way, it exhibits strange aspects that have led astronomers to classify it as peculiar.
Visible: DSS (left) and Visible: Color Ron & Beth Sharer, Steven White, AOP, KPNO, NOAO, NSF (right)
The visible-light images above reveal the general spiral nature of M106. Inclined to our line of sight, we see a bright central bulge surrounded by a thin disk containing spiral arms. The black-and-white DSS image is a long exposure, and hence the central regions are slightly saturated. Among the interesting features are patches of massive star formation within the disk, including a string of such supergiant H II regions at the southern edge of the inner (bright) disk. The point-like sources of light scattered throughout the field of view are, of course, foreground stars within our Milky Way Galaxy. The spectacular color photograph was obtained at the National Optical Astronomy Observatories . It reveals the presence of two primary spiral arms, one winding to the north and west (top and right), and the other stretching to the south and east (bottom and left). Thick dust lanes are prominent, particularly in the southern arm. The bluish tint reminds us that it is young and massive hot (blue-white) stars that are preferentially born in spiral arms.
Near-Infrared: 2MASS (left) Mid-Infrared: IRAS (center) and Far-Infrared: IRAS (right)
The 2MASS image is a near-infrared photograph. While the general characteristics of the inner galaxy remain evident, you can no longer see the dark dust. Near-infrared light corresponds to wavelengths longer than what the human eye can see, and it can easily pierce through the obscuration produced by dust. At longer infrared wavelengths, we measure the IR light that is actually emitted by the dust itself. This thermal infrared radiation is produced when the dust grains, often composed of silicates (much like sand), absorb the visible and ultraviolet photons from nearby stars. The dust grain is then heated slightly, and re-radiates at longer wavelengths, in the infrared portion of the electromagnetic spectrum.
The center and right images were obtained by the IRAS satellite in 1983, and are characterized by relatively poor spatial resolution. The mid-IR image corresponds to a wavelength of 25 microns. The photograph shows bright emission (in red) near the center. The elliptical shape of the emission peak is a consequence of the peculiar rectangular shape of the detectors used on IRAS. You can also see two other local peaks of mid-IR light north and south of the nucleus. These are due to supergiant H II regions, areas of massive star formations taking place within the inner spiral arms. The far-IR photo was obtained at a wavelength of 100 microns, and the infrared light is essentially unresolved. In other words, the spatial resolution (or visual acuity) of the detectors is not good enough to discern small details. In this case, the three peaks of emission seen in the mid-IR image blend into a single unresolved blob.
Radio: NVSS (left) and X-Ray: ROSAT (right)
The radio image of Messier 106 (above left) resembles a tadpole! The peak emission is color-coded as red, and weaker radio emission is denoted in yellow and green. The odd shape of the radio emission is suggestive of the peculiar nature of M106. This peculiarity is confirmed by the x-ray data (above right). Normal spiral galaxies are not typically strong x-ray sources. But M106 is not normal. Astronomers classify it as a Seyfert galaxy, one of the many types of active galaxies. Unlike normal galaxies, these active cousins produce large amounts of x-rays (and often radio emission) due to a central black hole within the galaxy nucleus.
This ultraviolet image shows the emission from hot stars and dust.
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