Passing star fed early solar system

A dying star straying close to the Sun may have supplied radioactive elements found in some of the oldest rocks in the solar system, recent research suggests.

The celestial visitor was around six times the size of the Sun and its passage came just as the planets were forming, more than four billion years ago, scientists say.

An international team led by Spanish astrophysicists came up with the idea to explain the mystery of how radioactive components found in the oldest known meteorites originated.

They concluded that these special isotopes could have come from a star in the final stages of its life that happened to be in the local neighbourhood. Under the theory, the star enriched the disk of gas and dust surrounding the young Sun. The elements then played an essential role in providing the building blocks of the rocky planets like Earth.

Astronomers are especially interested in primitive meteorites, called chondrites, because they are believed to be left over chunks of the original material that formed the planets. They can therefore tell us much about the early days of the solar system’s existence.

Previously it had been thought that the radioactive elements such as aluminium and iron came from a relatively nearby supernova, or exploding star, but the team say that observations do not fit that theory.

Instead, they suggest they were supplied by a star much less energetic or massive than a supernova. The model they have created supplies just the right proportion of radioactive isotopes to fit astronomers’ findings.

Josep Trigo, of the Catalonian Institute of Space Studies, said: “This new study provides the first astrophysical model that reproduces the abundances of these elements in chondrites, without the need to invoke the presence of a supernova in the solar neighbourhood during the initial moments of the formation of the Solar System.”

Colleague Anibal García Hernández, of the Instituto de Astrofísica de Canarias, said: “Thanks to this work, it has been shown that the proportion of radioactive isotopes estimated in our models of a star of six solar masses coincides with that measured in primitive meteorites.”

The research appeared in the journal Meteoritics and Planetary Science.

Picture: An artist’s impression of the visiting star’s brush with the cloud of gas and dust surrounding the Sun. (Credit: Instituto de Astrofísica de Canarias).

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