Space Telescope Finds "Blue Straggler" Stars in the
Core of a Globular Cluster 47 Tucanae
High resolution observations of the core of the globular cluster 47 Tucanae, made with the European Space Agency's Faint Object Camera (FOC) onboard NASA's Hubble Space Telescope (HST), provide new evidence that stars may collide and capture each other and gain a new "lease on life" in the process. The FOC observations reveal a surprisingly high concentration of a unique class of star called blue stragglers, which may evolve from "old age" back to a hotter and brighter "youth". These stars may also play a critical role in the dynamic evolution of the cluster's core.
The core of the globular cluster 47 Tucanae, as imaged by the European Space Agency's Faint Object Camera (FOC) onboard NASA's Hubble Space Telescope. Space Telescope's high spatial resolution and ultraviolet sensitivity make it a powerful tool for probing the centers of globular clusters. The FOC resolves several hundred stars where ground-based images only yield a few dozen stars. At least 21 of these stars are exceptionally bright in ultraviolet light. HST's UV sensitivity and high resolution allow it to easily separate these so-called blue stragglers stars from the red giant stars which dominate the cluster.
Blue stragglers may evolve from "old age" back to a hotter and brighter youth through stellar collisions and mergers. This high concentration of blue stragglers towards the core of 47 Tucanae suggests they are significantly more massive than most of the cluster's stars. Some of blue stragglers could be massive because they are really double star systems. Such binary systems may influence the motions of thousands of other stars within the cluster.
The FOC observations were made in ultraviolet light (2200 angstroms) on November 16, 1990 with the FOC in F/96 mode. Field of view is 11 X 11 arc seconds corresponding to a width of .75 light years, at 47 Tucanae's distance of 15,000 light years.
Faint Object Camera Instrument Definition Team: R. Albrecht, C. Barbieri, J. C. Blades, D. Barter, A. Boksenbeig, P. Crane, J. M. Deharveng, M. J. Disney, P. Greenfield, P. Jakobsen, R. Jerejewski, Kamperman, L R. King, F. Macchetto (Principal Investigator), C. D. Mackny, A. Nota, F. Paresce, W B. Sparks, G. Weigelt
Investigators: Francesco Paresce (ESAJuly 24, 1991 - STScI-1991-12/STScI). Michael Shara
(STScI), Georges Meylan
(ESA/STScI) - Credit: NASA/ESA