AN ABRASIVE COLLISION GIVES ONE GALAXY A "BLACK
A collision of two galaxies has left a merged star system with an
unusual appearance as well as bizarre internal motions. Messier 64
(M64) 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 M64 obtained with
the Hubble Space Telescope. M64 is well known among
amateur astronomers because of its appearance in
small telescopes. It was first cataloged in the
18th century by the French astronomer Charles Messier.
Located in the northern constellation Coma Berenices,
M64 resides roughly 17 million light-years from
At first glance, M64 appears to be a fairly normal pinwheel-shaped
spiral galaxy. As in the majority of galaxies, all of the stars in
M64 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 M64 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 M64
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 M64.
This image of M64 was taken with Hubble's Wide Field Planetary Camera
2 (WFPC2). The color image is a composite prepared by the Hubble
Heritage Team from pictures taken through four different color filters.
These filters isolate blue and near-infrared light, along with red
light emitted by hydrogen atoms and green light from Strömgren y.
Image Credit: NASA and The Hubble Heritage Team
Acknowledgment: S. Smartt (Institute of Astronomy)
and D. Richstone (U. Michigan)