Discovery of over a thousand variable stars in Terzan 5 and Liller 1 with JWST
The Bulge Fossil Fragments Terzan 5 and Liller 1 host some of the densest stellar environments in the Galaxy, yet their variable star populations have remained largely unexplored due to crowding and heavy obscuration. Here, we identify 1,315 variable sources in these two systems in what is to our knowledge the first JWST time-series variability census of a globular cluster-like object. By differencing consecutive non-destructive reads within each NIRCam integration, we transform sample-up-the-ramp imaging into an infrared movie sampled every 21 seconds. More than a century of observations has cataloged 5,604 variables, the majority of them pulsating stars, across 151 Galactic globular clusters. Our census alone 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, with zero previously known variables, now hosts 915, nearly double the count in the runner-up $ω$ Centauri. We detect dramatic infrared variability from the Rapid Burster, revealing the counterpart sought since 1976 (see Desai et al. 2026), and blindly recover a signal coincident with the prototype redback pulsar PSR J1748-2446A at its radio-timed orbital period, identifying the first optical or infrared counterpart to any of Terzan 5's pulsars. More broadly, we present a technique that recovers 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.