A common technique used in archaeology to establish the age of fossils and other organic samples from the past consists of measuring how much of a particular isotope of carbon, namely carbon-14 (14C), they contain. This radioactive isotope decays into the element nitrogen on a time scale of a few thousand years, hence the amount of it remaining in these ancient fossils is a strong indicator of the epoch from which they date. An analogous method, based on the radioactive decay of an unstable isotope of aluminium, has been recently exploited by astronomers to probe and assess the age of the Scorpius-Centaurus association, the closest group of very young and massive stars. Stellar age estimates can be then used to investigate how nearby massive stars have shaped our local region of the Milky Way.
“At the characteristic energy of the 26Al line, INTEGRAL has a spectral resolution over 60 times better than COMPTEL's, enabling us to study the intensity and shape of this line across the Galaxy in much greater detail,” comments Chris Winkler, INTEGRAL Project Scientist. “The data, gathered over five years, are so deep that it is now possible to isolate the contribution due to an individual, nearby stellar complex from the overall galactic 26Al emission,” adds Winkler.
Via stellar winds and supernova explosions, the stars in the Scorpius-Centaurus association are currently enriching the surrounding interstellar medium with heavy elements, including aluminium, and from the shape of the emission line of 26Al it is possible to constrain the kinematics of such ejecta. “By investigating the details of these outflows of radioactive gas, streaming at velocities of about 100 km/s towards the Sun, we are starting to unravel the recent history of massive star formation in the Solar System's vicinity and its implications on our own cosmic environment,” comments Diehl.
The new INTEGRAL data also allowed the astronomers to refine the estimate of the total content of 26Al in the Milky Way, which is lower by about 20 per cent than previous estimates. This is a critical step that is required to validate our understanding of the star formation and nucleosynthesis processes in our Galaxy and to predict the expected rate of supernova explosions.
Max-Planck Institute for Extraterrestrial Physics
University Observatory Munich, Germany
INTEGRAL Project Scientist
Research and Scientific Support Department
Directorate of Science and Robotic Exploration
ESA, The Netherlands