Throughout their life, stars undergo changes in their mass, pressure, composition and internal structure to, by exhausting their fuel and depending on their initial mass, give rise to a compact object such as a white dwarf, a neutron star or a black hole. It might be thought that this hectic evolution, which includes explosive episodes such as supernovae in the case of massive stars, should prevent stars from retaining characteristics of their early stages at the end of their lives. However, a study carried out by Antonio Claret, from the Andalusian Institute of Astrophysics (IAA-CSIC), concludes that,in a sense, the stars have “memories”.
Ismemory(in mathematical terms, thegamma function) is related to three stellar parameters: on the one hand, thepotential energy of the star, which arises from the fact that it is a sphere of self-gravitating gas; on the other, hismoment of inertia, which describes its resistance to turning and is linked to how the mass is distributed inside it (something similar to the case of a skater, who can modify her rotation speed by stretching or contracting her arms); and finally thedegree of compactness.
But what is truly fascinating is that, after the final stages of adulthood and the violent processes that occur when stars run out of fuel,once they reach their compact object phase (be it a white dwarf or a neutron star) they recover that constant value that they presented in their childhood. “It is curious that this function is lost to reappear in the final stages. It seems to behave like a fossil: after virtually disappearing, it returns to the scene and gives us information about the original organism,” says Claret, who has released his work in MagazineAstronomy & Astrophysic.
