Washington, Aug 22 (IANS): The fluorine in your toothpaste was likely formed billions of years ago in now dead stars of the same type as our sun, astronomers said.

The findings support the theory that fluorine is formed in stars similar to the sun but heavier, towards the end of their existence.

The sun and the planets in our solar system have then been formed out of material from these dead stars.

"So, the fluorine in our toothpaste originates from the sun's dead ancestors," said Nils Ryde, a reader in astronomy at Lund University in Sweden.

Together with colleagues from Ireland and the US, Ryde studied stars formed at different points in the history of the universe to see if the amount of fluorine they contain agrees with the predictions of the theory.

The researchers used a telescope in Hawaii and a new type of instrument that is sensitive to light with a wavelength in the middle of the infrared spectrum.

Whereas different chemical elements are formed at high pressure and temperature inside a star, fluorine is formed towards the end of the star's life, when it expands to become a red giant.

At that point, the fluorine moves to the outer parts of the star.

"The fluorine that is thrown out mixes with the gas surrounding the stars, known as the interstellar medium and from this medium are formed new stars and planets," Ryde explained.

The researchers will now try to find out whether fluorine could have been produced in the early universe, before the first red giants had formed.

They will also use the same method to study environments in the universe that are different from the environment surrounding the sun, such as close to the supermassive black hole at the centre of the Milky Way.