Washington: Black holes may be less simple and "clean" than how most theoretical model describe them, according to researchers.

A new research carried out by a group of scientists that includes Thomas Sotiriou, a physicist of the International School for Advanced Studies (SISSA) of Trieste, have suggested that black holes may be much "dirtier" than believed.

According to the traditional model, black holes are defined by only two quantities: mass and angular momentum (a black hole rotation velocity).

Once their progenitor has collapsed (a high mass star, for instance, that at the end of its life cycle implodes inwards) its memory is lost forever. All that is left is a quiescent black hole, with almost no distinctive features: all black holes, mass and angular momentum aside, look almost the same.

Sotiriou said that black holes, according to their calculations, may have hair, referring to a well-known statement by physicist John Wheeler , who claimed that "black holes have no hair," which means that mass and angular momentum are all one needs to describe them.

Sotiriou said that according to their calculations, the growth of the black hole's hair is accompanied by the emission of distinctive gravitational waves.