The collision of two galaxies has resulted in this, M64 (aka The Black Eye Galaxy). To the casual observer M64 looks fairly normal, except for the huge band of dust blocking part of our view of the nucleus. All its star orbit the galactic center in the same direction, clockwise in this image from Hubble, but recent observations show that the interstellar gas in the outer regions of M64 rotates in the opposite direction from the gas and stars in the inner regions. This is believed to trigger the creation of many new stars around the boundary between the regions where the oppositely rotating gases collide.
The small satellite galaxy that merged with its larger neighbour has now been almost completely destroyed. Its stars have either entered the main galaxy or scattered into intergalactic space, but signs of the collision persist in the retrograde motion of gas at the outer edge of M64.
Image Credit: NASA