Discovery of over a thousand variable stars in Terzan 5 and Liller 1 with JWST

Terzan 5 and Liller 1 are Bulge Fossil Fragments and host some of the densest stellar environments in the Galaxy, but their variable star populations have remained largely unexplored because of crowding and heavy obscuration. The new study identifies 1,315 variable sources in these two systems, which the authors describe as the first JWST time-series variability census of a globular cluster-like object.

To detect this variability, the team differenced consecutive non-destructive reads within each NIRCam integration, effectively transforming sample-up-the-ramp imaging into an infrared movie sampled every 21 seconds. More broadly, this demonstrates a technique for recovering group-level time-series photometry from JWST observations, enabling time-domain studies with an observatory whose field of view is naturally matched to the Galaxy's densest stellar systems.

For context, more than a century of observations has cataloged 5,604 variables, mostly pulsating stars, across 151 Galactic globular clusters. This single census amounts to 23 percent of that total and contains more photometrically variable binaries than had previously been cataloged in all globular clusters combined. The field of Liller 1, which had zero previously known variables, now hosts 915, nearly double the count in the runner-up omega Centauri.

The survey also detects dramatic infrared variability from the Rapid Burster, revealing the counterpart sought since 1976 (see Desai et al. 2026), and blindly recovers a signal coincident with the prototype redback pulsar PSR J1748-2446A at its radio-timed orbital period. That identifies the first optical or infrared counterpart to any of Terzan 5's pulsars. Together the results show JWST's ability to open time-domain studies of the Galaxy's most crowded stellar systems.