NASA's Hubble space telescope has captured the dance between two galaxies. These gravitationally interacting galaxies are located about 500 million light years from Earth in the constellation Tucana.

The pair of interacting galaxies is known as Arp-Madore and is a collection of strange galaxies. What is strange about this group? There are actually three galaxies, not just two. If you look at the upper arm of the small galaxy in the lower right corner of the image, you can see the knot-like structure.

As seen from Earth's perspective, astronomers have had difficulty distinguishing whether an object in space is one or more than one, or whether it stands in front of another. Astronomers discovered the third knot-like galaxy by analysing its speed and direction, which revealed that redshift, the wavelength of light "shifts" towards the red part of the spectrum, making it its own entity.

Image description: Two spiral galaxies. Each shines brightly in the centre, where a bar extends from side to side. The upper one is rounder and its arms form two thin rings. The lower galaxy is flatter and its arms form an outer ring; a dusty knot on its upper arm points to a third object. Where the galaxies come close together, gravity brings gas and dust together. A series of smaller galaxies surround them on a black background.