Fig8_10 How old is a globular star cluster

Fig8_10 How old is a globular star cluster

Fig. 8.10 . A plot of the luminosity (left vertical axis), in units of the Suns luminosity L, against the color index, B-V (bottom horizontal axis), for the stars in the southern globular star cluster 47 Tucanae, also designated NGC 104. The absolute visual magnitudes, MV, of the stars are also shown (right vertical axis). Although low mass, relatively faint stars are still on the main sequence (diagonal line from middle left to bottom right), the massive, bright stars in the cluster have left the main sequence and are evolving into giant stars (top right). Theoretical tracks, called isochrones, show the evolutionary distributions at different ages of 10, 12, 14 and 16 billion years from top to bottom and left to right. The best fit to the observed data corresponds to an age of between 12 and 14 billion years for this star cluster. (Courtesy of James E. Hesser.)

Copyright 2010, Professor Kenneth R. Lang, Tufts University