ASU: Webb Telescope Uncovers Star Clusters in Cosmic Gems Arc

In the early universe, young galaxies underwent significant bursts of star formation, producing large amounts of ionizing radiation. However, their great distances have made direct studies of their stellar content challenging.

Using the James Webb Space Telescope (JWST), an international team of astronomers, including Arizona State University Regents and Foundation Professor Rogier Windhorst, has detected five young, massive star clusters in the Cosmic Gems arc (SPT0615-JD1). This galaxy, which is strongly lensed, emits light from when the universe was approximately 460 million years old, covering 97% of cosmic history. These findings have been published in the journal Nature.

Historical Context

The Cosmic Gems arc was initially discovered through images taken by the NASA/ESA Hubble Space Telescope as part of the Reionization Lensing Cluster Survey (RELICS) program. This program studied the lensing galaxy cluster SPT-CL J0615−5746. The Hubble Space Telescope has been instrumental in studying local galaxies, but the JWST offers a unique opportunity to study star formation and the inner workings of infant galaxies at unprecedented distances.

Key Discoveries

• Gravitational Lensing: The Cosmic Gems arc benefits from gravitational lensing, which allows astronomers to resolve the galaxy down to parsec scales.
• JWST Capabilities: The JWST’s sensitivity and angular resolution at near-infrared wavelengths, combined with gravitational lensing, enabled this discovery. No other telescope could have made this discovery.
• Star Clusters: The newly detected star clusters in the Cosmic Gems arc are massive, dense, and located in a very small region of their galaxy. They contribute the majority of the ultraviolet light coming from their host galaxy and are significantly denser than nearby star clusters.

Scientific Implications

• Proto-Globular Clusters: The discovery provides direct evidence that proto-globular clusters formed in faint galaxies during the reionization era, contributing to our understanding of how these galaxies reionized the universe.
• Galaxy Evolution: The high stellar densities found in the clusters offer insights into the processes taking place in their interiors, including the possible formation of very massive stars and black hole seeds, which are crucial for galaxy evolution.

Future Research

The team plans to conduct further observations and spectroscopy with the JWST. They aim to study the galaxy with JWST’s NIRSpec and MIRI instruments in Cycle 3. These observations will help confirm the redshift of the galaxy, study the ultraviolet emission of the star clusters, and examine the properties of ionized gas. The spectroscopic observations will also allow for spatial mapping of the star formation rate.

Summary

• Discovery: Five young, massive star clusters detected in the Cosmic Gems arc using JWST.
• Historical Context: Initial discovery by Hubble Space Telescope as part of the RELICS program.
• Gravitational Lensing: Enabled detailed resolution of the galaxy.
• Scientific Implications: Insights into proto-globular clusters, galaxy reionization, and galaxy evolution.
• Future Research: Further observations with JWST’s NIRSpec and MIRI instruments planned.

This discovery underscores the JWST’s potential to push the boundaries of our understanding of the early universe and the formation of the first stars and galaxies.