Uma estrela muito, muito velha!

Fonte e figura original aqui.

Novos estudos indicam que a "Estrela Matusalém" ou HD 140283 possui cerca de 14,5 bilhões de anos, com uma margem de erro de 0,8 bilhão para mais ou para menos - o que significa que ela pode ter de 13,7 a 15,3 bilhões de anos. Isso significa que ela começou a brilhar logo depois do nascimento do Universo. Esse novo cálculo da idade de HD 140283 foi feito usando observações feitas pelo telescópio Hubble.

Ela se encontra hoje em um estágio evolutivo de "sub-gigante", ou seja, está saindo da sequência principal e se expandindo, pois o seu estoque de hidrogênio no núcleo está quase esgotado e já foi iniciada a queima de hélio. O Sol deve entrar nessa fase daqui uns 5 bilhões de anos.

Para saber mais:

HD 140283: A Star in the Solar Neighborhood that Formed Shortly After the Big Bang (1)

Howard E. Bond, Edmund P. Nelan, Don A. VandenBerg, Gail H. Schaefer and Dianne Harmer.

HD 140283 is an extremely metal-deficient and high-velocity subgiant in the solar neighborhood, having a location in the HR diagram where absolute magnitude is most sensitive to stellar age. Because it is bright, nearby, unreddened, and has a well-determined chemical composition, this star avoids most of the issues involved in age determinations for globular clusters. Using the Fine Guidance Sensors on the Hubble Space Telescope, we have measured a trigonometric parallax of 17.15 ± 0.14 mas for HD 140283, with an error one-fifth of that determined by the Hipparcos mission. Employing modern theoretical isochrones, which include effects of helium diffusion, revised nuclear reaction rates, and enhanced oxygen abundance, we use the precise distance to infer an age of 14.46 ± 0.31 Gyr. The quoted error includes only the uncertainty in the parallax, and is for adopted surface oxygen and iron abundances of [O/H] = −1.67 and [Fe/H] = −2.40. Uncertainties in the stellar parameters and chemical composition, especially the oxygen content, now contribute more to the error budget for the age of HD 140283 than does its distance, increasing the total uncertainty to about ±0.8 Gyr. Within the errors, the age of HD 140283 does not conflict with the age of the Universe, 13.77 ± 0.06 Gyr, based on the microwave background and Hubble constant, but it must have formed soon after the big bang.

(1) Based in part on observations made with the NASA/ESA Hubble Space Telescope, obtained by the Space Telescope Science Institute. STScI is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS5-26555.

Fonte: http://arxiv.org/abs/1302.3180.

Para saber mais: g1.com.br/ciencia.