Astrobiology: Prescient words on comets and life
Nature 516, 7531 (2014). doi:10.1038/516329a
Author: Milton Wainwright
The landing of the Philae probe on comet 67P/Churyumov–Gerasimenko last month has led to speculation that comets might have delivered the building-block elements of life to Earth — an idea anticipated by the French astronomer Camille Flammarion more than a century ago in his 1880
The exclusion of a significant range of ages in a massive star cluster
Nature 516, 7531 (2014). doi:10.1038/nature13969
Authors: Chengyuan Li, Richard de Grijs & Licai Deng
Stars spend most of their lifetimes on the main sequence in the Hertzsprung–Russell diagram. The extended main-sequence turn-off regions—containing stars leaving the main sequence after having spent all of the hydrogen in their cores—found in massive (more than a few tens of thousands of solar masses), intermediate-age (about one to three billion years old) star clusters are usually interpreted as evidence of internal age spreads of more than 300 million years, although young clusters are thought to quickly lose any remaining star-forming fuel following a period of rapid gas expulsion on timescales of order 107 years. Here we report, on the basis of a combination of high-resolution imaging observations and theoretical modelling, that the stars beyond the main sequence in the two-billion-year-old cluster NGC 1651, characterized by a mass of about 1.7 × 105 solar masses, can be explained only by a single-age stellar population, even though the cluster has a clearly extended main-sequence turn-off region. The most plausible explanation for the existence of such extended regions invokes a population of rapidly rotating stars, although the secondary effects of the prolonged stellar lifetimes associated with such a stellar population mixture are as yet poorly understood. From preliminary analysis of previously obtained data, we find that similar morphologies are apparent in the Hertzsprung–Russell diagrams of at least five additional intermediate-age star clusters, suggesting that an extended main-sequence turn-off region does not necessarily imply the presence of a significant internal age dispersion.