In the open cluster Trumpler 5, where hundreds of stars move together, one star behaves like a teenager among elders. It pulsates — expanding and contracting, changing brightness every few hours. Such pulsating stars, classical Cepheids and RR Lyrae, are typically considered contemporaries of ancient globular clusters: they are over 10 billion years old. But this star, judging by its motion and chemistry, is only 2–5 billion years old.
Astronomers aimed two powerful telescopes at it, PEPSI on the Large Binocular Telescope and GHOST on the Gemini-South telescope, and captured its spectrum, like fingerprints. By measuring the star's velocity from several observations, they found it is moving at 50.57 km/s, while the cluster itself moves at 50.76 km/s. The probability of a chance coincidence is two thousandths of a percent. The star is definitely part of this family.
So, RR Lyrae stars are not always old and metal-poor. Some are born in the galaxy's disk, like our Sun, and live only a couple of billion years. This breaks the established picture: previously, one such star could date an entire cluster as ancient. Now we must be more careful — age can be deceptive.
The cluster Trumpler 5 is located in the constellation Puppis and is about 2.5 thousand light-years away. Its age is estimated at 2–5 billion years — similar to our Sun.
In Stanislaw Lem's novel 'Solaris', the planet's ocean pulsates, changing its shape, a distant metaphor for stellar pulsations.