Astronomers Capture Images of Massive White Dwarf Exodus for the First Time Ever

For the first time ever, astronomers have captured images of fledgling white dwarf stars beginning their migration from the crowded center of an ancient star cluster to the less populated "suburbs." The new findings tell scientists a bit more about the evolution of these stars.

White dwarfs are actually 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 star cluster's packed downtown. This migration is caused by an internal fight within the cluster; globular star clusters sort out stars according to their mass, which means that the result is that heavier stars slow down and sink to the cluster's core while lighter stars speed up and move to the edge. Until now, though, astronomers had never had evidence of this process occurring in action.

In this case, the astronomers used Hubble to watch the white dwarfs in a globular star cluster called 47 Tucanae. This cluster is composed of a dense swarm of hundreds of thousands of stars in our Milky Way galaxy. The cluster resides 16,700 light-years away in the southern constellation Tucana.

"We've seen the final picture before: white dwarfs that have already sorted themselves out and are orbiting in a location outside the core that is appropriate for their mass," said Jeremy Heyl, one of the researchers, in a news release. "But in this study, which comprises about a quarter of all the young white dwarfs in the cluster, we're actually catching the stars in the process of moving outward and segregating themselves according to mass. The entire process doesn't take very long, only a few hundreds of millions of years, out of the 10-billion-year age of the cluster, for the white dwarfs to reach their new home in the outer suburbs."

As the white dwarfs move, they'll become cooler and less luminous because they have no cuclear sources of energy. These findings reveal a bit more about the evolution of globular clusters and shows what happens to white dwarfs during interactions with larger stars.

The findings are published in The Astrophysical Journal.

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