Centaurus A galaxy, optical image. This large elliptical galaxy is crossed by a wide, dark lane of dust. The galaxy appears mainly yellow/orange as its stars are mainly old and red, but the area around the dust lane is much bluer. This is indicative of young stars and starbirth. It is thought that the dust lane is a remnant of a spiral galaxy that collided with the elliptical galaxy many millions of years ago. The collision triggered a wave of starbirth. The galaxy is a powerful emitter of radio waves, and also emits X- rays and gamma radiation. Its emissions are thought to derive from a huge black hole at the galaxy's heart.