Rubin Observatory Peers Deep Into the Famous COSMOS Field

The COSMOS field — the Cosmic Evolution Survey Deep Field — is one of the most studied patches of sky, in the constellation Sextans. The Hubble Space Telescope (HST) photographed it in segments from 2003 to 2005 using its Advanced Camera for Surveys (ACS), stitched into a picture of cosmic evolution.

The National Science Foundation–Department of Energy (NSF–DOE) Vera C. Rubin Observatory has observed the same region, capturing its most detailed view yet of hundreds of thousands of galaxies and stars. It is the first time Rubin's Legacy Survey of Space and Time (LSST) Camera — the world's most powerful camera — has produced an image and catalog for scientific research.

Astronomers have studied the COSMOS field for over two decades using leading telescopes, making it a reference for testing new instruments. Phil Marshall, deputy director of Rubin Observatory at SLAC National Accelerator Laboratory (SLAC), said the field's wealth of prior observations makes it valuable. Its repeated targeting will make it a useful testing ground as scientists prepare for the survey's data.

The image was released with Rubin's Early Data Preview 2 (EDP2), Data Preview 2's first phase, combining observations from April 2025 to January 2026 during science validation. Bob Blum, director of Rubin Observatory at NSF's National Optical-Infrared Astronomy Research Laboratory (NOIRLab), said the image is only the beginning for Rubin here. Repeated visits in coming years will reveal many transient and variable objects, such as supernovae, for study.

The picture stacks hundreds of observations from the LSST Camera's 3.2-gigapixel sensor and contains over half a million galaxies and over 50,000 stars. These include barred spirals, smooth ellipticals, faint red galaxies and merging galaxies. The stars belong to the Milky Way and lie along the line of sight, but the camera avoids the galaxy's crowded plane. This kept the disk's dust and gas, or interstellar medium (ISM), from obscuring the image, letting it see farther into space and time.