An Extrasolar Perspective

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Science  18 Oct 2013:
Vol. 342, Issue 6156, pp. 291
DOI: 10.1126/science.342.6156.291-b

White dwarfs represent the end stage in the evolution of Sun-like stars. There is evidence that the atmospheres of some of them contain material from planetesimals shredded after their orbits passed too close to the dying star. Jura et al. examined the iron-to-aluminum abundance ratio in the atmospheres of seven white dwarfs with well-measured abundances and found that this ratio varies by more than a factor of 100 across the sample. The authors attribute this variation to igneous differentiation, which concentrates iron in cores and aluminum in crusts, and to impacts and collisions between planetesimals, which vary the iron-to-aluminum ratio. The heat source for igneous differentiation must have come from the radioactive decay of 26Al—a radioisotope that was an important short-term heat source in the early solar system and which is produced within massive stars and injected into the interstellar medium through stellar explosions or stellar winds. The inferred abundance of 26Al in the extrasolar environments where the shredded planetesimals formed is similar to that inferred for the early solar system. Thus, the conventional view that our solar system was unusual in its initial 26Al abundance may not be justified.

Astrophys. J. 775, L41 (2013).

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