A collision of two galaxies has left a merged star system with an unusual appearance as well as bizarre internal motions. Messier 64 (M 64) has a spectacular dark band of absorbing dust in front of the galaxy's bright nucleus, giving rise to its nicknames of the 'Black Eye' or 'Evil Eye' galaxy.
Fine details of the dark band are revealed in this image of the central portion of M 64 obtained with the Hubble Space Telescope. M 64 is well known among amateur astronomers because of its appearance in small telescopes. It was first catalogued in the 18th century by the French astronomer Messier. Located in the northern constellation Coma Berenices, M 64 resides roughly 17 million light-years from Earth.
At first glance, M 64 appears to be a fairly normal pinwheel-shaped spiral galaxy. As in the majority of galaxies, all of the stars in M 64 are rotating in the same direction, clockwise as seen in the Hubble image. However, detailed studies in the 1990's led to the remarkable discovery that the interstellar gas in the outer regions of M 64 rotates in the opposite direction from the gas and stars in the inner regions.
Active formation of new stars is occurring in the shear region where the oppositely rotating gases collide, are compressed, and contract. Particularly noticeable in the image are hot, blue young stars that have just formed, along with pink clouds of glowing hydrogen gas that fluoresce when exposed to ultraviolet light from newly formed stars.
Astronomers believe that the oppositely rotating gas arose when M 64 absorbed a satellite galaxy that collided with it, perhaps more than one billion years ago. This small galaxy has now been almost completely destroyed, but signs of the collision persist in the backward motion of gas at the outer edge of M 64.
This image of M 64 was taken with Hubble's Wide Field Planetary Camera 2 (WFPC2). The colour image is a composite prepared by the Hubble Heritage Team from pictures taken through four different colour filters. These filters isolate blue and near-infrared light, along with red light emitted by hydrogen atoms and green light from Stroemgren y.