NASA has shared footage of an 'incredibly rare' brown dwarf that could be up to 13 billion years old, named 'The Accident' after being discovered by chance. 

A brown dwarf is a mysterious object that sits somewhere between a gas giant planet and a small star, but without the size to fuse hydrogen like a star would.

There might be more of these unusual 'stars' lurking in our galaxy than previously thought, according to a study by astronomers at Caltech in Pasadena, California.

Named WISE 1534–1043, it is 50 light years from the Earth and doesn't resemble any of the 2,000 brown dwarfs found in our galaxy so far, the NASA researchers said. 

It is faint in some wavelengths of light, bright in others, and hurtling around the Milky Way at half a million miles per hour - faster than any other local brown dwarf. 

The unusual light make-up and speed helped the team determine it is between 10 and 13 billion years old - double the average age of other known brown dwarfs and dating to when the Milky Way was very young and had a different chemical makeup.

This suggests they have been around in the Milky Way since the earliest days and meaning there could be more than first thought, with a hidden population of up to 100 billion brown dwarfs floating in interstellar space.

The brown dwarf was accidentally discovered via the Wide-field Infrared Survey Explorer (NEOWISE) by citizen scientist Dan Caselden, who was using an online program he built to find these objects in data gathered by the telescope.