Cepheid Variable Star P42 in NGC 5468

At the center 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 they are 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.

About the colours

The images are separate exposures acquired by the NIRCam instrument on the James Webb Space Telescope (left) and the WFC3/IR instrument on the Hubble Space Telescope (right).

About the data

This image was created with Webb and Hubble data from proposals: 1685 and 11570 (A. Riess). Image processing: Alyssa Pagan (STScI).