Stars are born from huge clouds of gas and dust. Many of the stars remain close together, forming clusters. But as a cluster moves through the Milky Way, it gets pulled apart. The gravity of the rest of the galaxy tugs away the stars on the outskirts of the cluster. It also loosens the rest of the cluster, making it easier to pull away more stars.

A recent study looked at how that’s played out in the region around the Pleiades cluster. Using telescopes in space and on the ground, researchers measured how fast the stars in the region are spinning. That provides a rough measure of their age – the younger the star, the faster it spins. They also measured the motions of the stars through the galaxy, allowing them to trace the paths of the stars far into the past. And they compared the compositions of the stars; stars that were born together are made of the same mixture of elements.

From that, they found that the Pleiades and several smaller groups were close together tens of millions of years ago. That suggests they were born together before heading their separate ways. The study also found hundreds of stars between the groups that had belonged to one of the groups in the past. Today, the groups and loners are spread across 2,000 light-years of space – the Giant Pleiades Complex.

Look for the Pleiades high overhead at nightfall. It looks like a tiny dipper – the heart of a once larger family of stars.

Script by Damond Benningfield