M99, located in the constellation Coma Berenices approximately 50 million light-years from the Earth, is a classic example of a spiral galaxy seen almost face on. The galaxy has been distorted with one of it spiral arms less tightly wound than the other. Recent research has offered one explanation for the cause of this distortion. It is postulated that the gravitational influence of a passing dark galaxy is responsible. Dark galaxies have no visible stars and are mainly comprised of dark matter. Such galaxies are still the subject of debate, but recent evidence tends to support their existence.
The image above was assembled using two filtered images. The red channel is composed of a near infrared filtered image (F814W) and the blue channel is composed of an ultraviolet filtered image (F336W). A synthetic green channel image was used. This green channel image consisted of a combination of the near infrared and ultraviolet filtered images. These three images were combined to produce the color image displayed above.
1Based on observations made with the NASA/ESA Hubble Space Telescope, and obtained from the Hubble Legacy Archive, which is a collaboration between the Space Telescope Science Institute (STScI/NASA), the Space Telescope European Coordinating Facility (ST-ECF/ESA) and the Canadian Astronomy Data Centre (CADC/NRC/CSA).