Stars reveal their age
Astronomers have made a ground-breaking discovery, revealing that while the stars in the sky are old, clusters (spherical collections of stars) are still young. Astronomers using the NASA/ESA (National Aeronautics and Space Administration and European Space Agency) Hubble Space Telescope have published their findings in the scientific journal Nature.
Globular clusters are spherical collections of stars, tightly bound to each other by their mutual gravity, and classed as relics of the early years of the Universe, with ages of typically 12-13 billion years. There are around 150 globular clusters in the Milky Way, which contain many of the galaxy's oldest stars.
The project, led by Professor Francesco Ferraro, is titled 'Star Clusters as Cosmic Laboratories for Astrophysics, Dynamics and Fundamental Physics' (COSMIC-LAB). The European Research Council (ERC) is providing funding of EUR 1.8 million over a duration of 5 years.
Professor Ferraro says, 'Although these clusters all formed billions of years ago, we wondered whether some might be aging faster or slower than others. By studying the distribution of a type of blue star that exists in the clusters, we found that some clusters had indeed evolved much faster over their lifetimes, and we developed a way to measure the rate of aging.'
Star clusters form in a short period of time, although all the stars within them are the same age. However, because bright, high-mass stars burn up their fuel quite quickly, globular clusters are old so there should only be low-mass stars within them. Under certain circumstances, however, stars can be given a new burst of life, receiving extra fuel that bulks them up and substantially brightens them. This can happen if two neighbouring stars merge together, or if they collide. These reinvigorated stars are called blue stragglers, because of their blue colour, and the fact that their evolution lags behind that of their neighbours. These specific stars, with their high mass and brightness, lie at the heart of this unique study.
To better understand cluster ageing, Professor Ferraro's team mapped the location of blue straggler stars in 21 globular clusters. Subsequently, they found that a few clusters appeared young, with blue straggler stars distributed throughout, while a larger group appeared old, with the blue stragglers clumped in the centre. A third group was in the process of ageing, with the stars closest to the core migrating inwards first. This observational group also had ageing stars farther out, which appeared to be progressively sinking towards the centre.
Professor Barbara Lanzoni, who is part of Professor Ferraro's research team, says, 'Since these clusters all formed at roughly the same time, this reveals big differences in the speed of evolution from cluster to cluster. In the case of fast-aging clusters, we think that the sedimentation process can be complete within a few hundred million years, while for the slowest it would take several times the current age of the Universe.'
This study provides the first empirical evidence of how quickly different globular clusters age.
Data Source Provider: Nature
Document Reference: Based on information from the journal Nature
Subject Index: Scientific Research; Space & satellite research