Messier 94 is a spiral galaxy with a prominent central bulge and tightly wound spiral arms.
Visible: DSS and Visible: Color - KPNO
The black-and-white visible-light photo (above left) is a long-exposure image in which the galaxy's inner disk is intentionally over-exposed. [The spiral structure of M94 and the presence of dust lanes in the disk is more clearly revealed in a shorter exposure image.] The most interesting feature of the DSS image is the faint and broad ring of light surrounding the galaxy disk (its diameter is nearly as large as the field of view). Such rings represent density enhancements in the galaxy's gas, dust and stellar constituents. These rings may be the result of a gravitational encounter with another galaxy in the distant past. For a remarkable Hubble Space Telescope image of a ring galaxy, click here
The false-colored image (above right) was obtained at the Kitt Peak National Observatory (KPNO). By clicking on the photo in the image matrix at the top of this page, you can see the spiral nature of the disk and also discern lanes of obscuring dust. Moreover, the entire inner disk appears to be immersed within a fainter outer disk.
The near-infrared view of Messier 94 is not much different than the visible images discussed above. A bright central bulge is seen within a faint outer disk of light. By clicking within the image matrix at the top of the page, you find that the dust lanes within M94 have diminished. This is because near-infrared light is an effective means to pierce through the obscuration caused by dust.
Mid-Infrared: IRAS and Far-Infrared: IRAS
The longer wavelength infrared images of Messier 94 are false-colored, with red denoting the brightest light and blue indicating the faintest. In the mid-IR image (above left), the galaxy is seen as a point source, with the light stretched into an oval. This is a consequence of the peculiar rectangular shape of the detectors used aboard the IRAS satellite. The faint blue light seen scattered throughout the field of view is simply random noise, similar to static heard on a radio. The far-infrared photograph again demonstrates that Messier 94 remains unresolved by IRAS. In other words, the detector size was larger than the angular extent of the galaxy, and hence we cannot discern any features within M94. If you look very closely, you might see the suggestive trace of an outer ring (in dark blue). Scientists normally demand that such features have a higher signal-to-noise ratio before drawing any firm conclusions about its reality.
The radio image of Messier 94 has a similar color scheme as the IRAS infrared images. The galaxy is again unresolved, and our view of the galaxy is that of a point source. The surrounding blue and purple signals are merely random noise, and are not real. The greenish blob located to the southwest (lower right) could be a weak background radio source (such as a quasar), although no such cataloged object exists in the NASA/IPAC Extragalactic Database.
Although the x-ray image is of relatively low spatial resolution, we can clearly see weak x-ray emission centered on the galaxy position. "Normal" spiral galaxies are not typically strong emitters of x-rays. Messier 94, however, is one of the closest examples of a LINER (Low-Ionization Nuclear Emission-line Region), a type of active galaxy. LINERs are characterized by extremely bright, starlike central nuclei (see visible-light images above), and are low-luminosity cousins of Seyfert galaxies. While normal (spiral) galaxies radiate primarily at optical and infrared wavelengths, active galaxies tend to have significant x-ray and synchrotron radio emission. The source of x-rays is likely to be an active galactic nucleus (AGN).
Ultraviolet: ASTRO-2 UIT
Finally, we come to the fascinating ultraviolet image of Messier 94. At first glance, it looks like a picture of the Ring Nebula (Messier 57)! In reality, the image reveals why M94 is also regarded as a starburst galaxy. This special nomenclature is reserved for spiral galaxies that are experiencing an era of unusually massive star formation. We see a well-defined ring of newborn stars (less than 10 million years old) surrounding the galaxy nucleus. Astronomers are busy studying the starburst phenomena, and trying to understand why such activity is limited to a discrete ring within the galaxy disk.