Orphan Stars: How to Find Their Home express
Blue giant stars are usually born in tight stellar nurseries — open clusters within the thin disk of our Galaxy. But sometimes such stars are found high above the disk, as if thrown out of their home. How did they get there? Astronomers decided to run a "paternity test": take 39 such orphan stars and 447 clusters, and trace their paths backward in time using Gaia telescope data.
Gaia measures star positions and velocities with incredible precision. The scientists rewound the cosmic film tens of millions of years and checked whether the trajectories of stars and clusters crossed. If they did, the star could have been ejected from that cluster. To verify, they compared the ages of the star and cluster using color-magnitude diagrams — a kind of stellar passport. Five pairs matched.
For each of the five stars, they estimated the ejection speed and travel time. The mechanisms turned out to be different: some were flung out by a neighboring supernova explosion, others by a gravitational slingshot during close encounters in the cluster core.
So "stellar orphans" find their families. And that one star that doesn't fit the pattern reminds us that the Galaxy still holds many surprises.
The Gaia telescope is so precise that it can measure the angle subtended by a coin on the Moon as seen from Earth.
In the series "Star Trek," there's an episode where a runaway star carries a planet with it — a scenario that could actually happen during an ejection from a cluster.