Free Astronomy Magazine July-August 2015

SPACE CHRONICLES challenge our ideas about how and when a star loses its mass near the end of its life. White dwarfs are the burned-out rel- ics of ancient stars that rapidly shut down their nuclear furnaces, cooling down and losing mass at the end of their active lives. As these stellar car- casses age and shed mass, they are expelled from the densely packed centre of the globular cluster and migrate to wider orbits. Hubble traces the migration of white dwarfs in cluster 47 Tucanae by NASA A stronomers using the NASA/ ESA Hubble Space Telescope have, for the first time, collect- ed a census of young white dwarf stars be- ginning their migra- tion from the crowd- ed centre of an an- cient star cluster to its less populated out- skirts. The new results T he heart of the giant globular star cluster 47 Tuca- nae in the Hubble Space Telescope image at left reveals the glow of 200,000 stars. The green box outlines the clus- ter's crowded core, where Hubble spied a parade of young white dwarfs start- ing their slow-paced 40-million-year jour- ney to the less pop- ulated suburbs. The stellar relics are too faint to be seen clearly in visible light, as shown in the Hubble image at top right. But in ultravio- let light the stars glow brightly because they are extremely hot, as shown in the image at bottom right, taken by Hubble's Wide Field Camera 3. The green circles in the image outline the brightest of the young white dwarfs spied by Hubble. [NASA, ESA, and H. Richer and J. Heyl (University of British Columbia, Vancouver, Canada)]