White Dwarfs Migrating from Globular Cluster 47 Tucanae's Core
The heart of the giant globular star cluster 47 Tucanae in the Hubble Space Telescope image at left reveals the glow of 200,000 stars. The green box outlines the cluster's crowded core, where Hubble spied a parade of young white dwarfs starting their slow-paced 40-million-year journey to the less populated suburbs.
White dwarfs are the burned-out relics of stars that rapidly lose mass, cool down, and shut off their nuclear furnaces. As these glowing carcasses age and shed weight, their orbits begin to expand outward from the cluster's packed downtown. This migration is caused by a gravitational tussle among stars in the cluster.
The stellar relics are too faint to be seen clearly in visible light, as shown in the Hubble image at top right. But in ultraviolet 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.
Astronomers used Hubble to analyze 3,000 white dwarfs in the cluster, located 16,700 light-years away in our Milky Way galaxy's southern constellation of Tucana. Until these Hubble observations, astronomers had never seen the dynamical conveyor belt in action. The Wide Field Camera 3 observations were taken between November 2012 and December 2013. The left-hand image and the image at top right are a blend of exposures taken by the Advanced Camera for Surveys and Wide Field Camera 3.