By Dr David Whitehouse BBC News Online science editor

M64 is well known among amateur astronomers

The galaxy M64 has a dark band of dust in front of its bright nucleus, giving rise to its nicknames of the "Black Eye" or "Evil Eye" galaxy.

Observations made by the Hubble Space Telescope show that gas in the galaxy flows one way in the centre and in the opposite direction further out.

This strange behaviour is the result of a galactic collision, say scientists.

Blue stars, pink clouds

M64 is well known among amateur astronomers because of its appearance in small telescopes. It is roughly 17 million light-years distant located in the northern constellation of Coma Berenices.

It was first catalogued in the 18th Century by the French astronomer Messier who included it in his famous catalogue of celestial objects.

At first glance, it seems 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, recent detailed studies 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.

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.

The Hubble image shows that new stars are being formed 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.

The small galaxy that impinged on its neighbour has now been almost completely destroyed. Its stars either merged with the main galaxy or were scattered into the vastness of intergalactic space.