Comparison of Hubble and Webb views of a Cepheid variable star

At the centre of these side-by-side images is a special class of star used as a milepost marker for measuring the Universe’s rate of expansion — a Cepheid variable star. The two images are very pixelated because each is a very zoomed-in view of a distant galaxy. Each of the pixels represents one or more stars. The image from the James Webb Space Telescope is significantly sharper at near-infrared wavelengths than Hubble (which is primarily a visible-ultraviolet light telescope). By reducing the clutter with Webb’s crisper vision, the Cepheid stands out more clearly, eliminating any potential confusion. Webb was used to look at a sample of Cepheids and confirmed the accuracy of the previous Hubble observations that are fundamental to precisely measuring the Universe’s expansion rate and age.

[Image description: A horizontal two-panel image of pixelated, black-and-white star fields. The left image is labelled Webb Near-IR and has a few dozen points of light of varying brightness. At the centre of the image, one bright point is circled. The right image is labelled Hubble Near-IR and has more indistinct, blurry patches whose overall brightness is similar to the more defined regions in the left image. At the centre, a light grey pixel is circled.]