A newly discovered star with a primitive chemical composition has left scientists to rethink previous star formation models.

The rare 13-billion-year old star, one of only four 'primitive' stars ever found has a mass slightly less than the Sun's. The star called SDSS J102915+172927, was found in the constellation Leo about 3,500 light years above the disc of the Milky Way Galaxy.

The intriguing star's discovery is reported in a study published in the journal Nature. The star has a number of unique features including its size which is just four-fifths of the Sun's mass.

"It was believed that stars with masses lower than even the Sun's mass actually can't form from matter that contains so little carbon and oxygen," said co-author Hans Ludwig, from the University of Heidelberg.

Scientists believe that smaller stars are formed because of high concentrations of carbon and oxygen atoms that provide the pressure needed to ignite the gas at the core of the star. Since this new star formed without the help of these elements, scientists are scrambling for new star formation theories.

"The common wisdom is that a low-mass star cannot be formed before it is enriched by a minimum amount of materials," said an author of the study, Piercarlo Bonifacio of the Paris Observatory in France.

Another inexplicable feature of the star is its lack of lithium. Most old stars have lithium and this star has at least 40 times less lithium than expected. Scientists have no idea where the lithium went or why it disappeared.

Scientists are now looking for more primitive stars to compare this odd star. Researchers have suggested that there are between five and fifty other stars that can be discovered in the Sloan Digital Sky Survey.

"The thing I'm looking forward to is finding out whether this one is a freak one, or whether other stars at this metallicity show an absence of lithium," Bonifacio said. "We do have other candidates."