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HubbleSite Hubble Catches a Stellar Exodus in Action


Space Telescope Science

Globular star clusters are isolated star cities, home to hundreds of thousands of stars. And like the fast pace of cities, there's plenty of action in these stellar metropolises. The stars are in constant motion, orbiting around the cluster's center. Past observations have shown that the heavyweight stars live in the crowded downtown, or core, and lightweight stars reside in the less populated suburbs.

But as heavyweight stars age, they rapidly lose mass, cool down, and shut off their nuclear furnaces. After the purge, only the stars' bright, super-hot cores remain, and they are called white dwarfs. This weight-loss program causes the now lighter-weight white dwarfs to be nudged out of the downtown through gravitational interactions with the heftier stars. At each encounter, the white dwarfs' orbits begin to expand outward from the cluster's packed center. Until these Hubble observations, astronomers had never seen the dynamical conveyor belt in action. The new Hubble results reveal young white dwarfs on their slow-paced 40-million-year exodus from the bustling center of the globular cluster 47 Tucanae in our Milky Way galaxy.

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