Astronomy

Phoenix galaxy cluster mapped by Webb

Thursday, February 20, 2025

The Phoenix galaxy cluster was mapped by NASA’s Webb Telescope, revealing how intermediate-temperature gas fuels extreme star formation despite a massive black hole. This discovery confirms a long-standing theory and provides new insights into galaxy cluster evolution.

Researchers using NASA’s James Webb Space Telescope have confirmed how a massive galaxy cluster sustains high rates of star formation, resolving a long-standing mystery. This finding builds on more than a decade of studies conducted with NASA’s Chandra X-ray Observatory and Hubble Space Telescope, along with several ground-based observatories.

Image credit: NASA, CXC, NRAO, ESA, M. McDonald (MIT), M. Reefe (MIT), J. Olmsted (STScI)

Webb maps full picture of how the Phoenix galaxy cluster forms stars

The Phoenix cluster, located 5.8 billion light-years from Earth, has drawn interest due to its extreme gas cooling and rapid star formation, despite hosting a supermassive black hole of roughly 10 billion solar masses. In most galaxy clusters, the central black hole emits energetic particles and radiation that prevent gas from cooling enough to form stars. However, the Phoenix cluster defies this trend, prompting researchers to investigate the mechanisms driving its unusual star formation.

Webb has now mapped the missing link, warm gas within the cluster’s core, that ultimately fuels star formation. This gas, at an intermediate temperature, was found within cavities containing both extremely hot gas at 18 million degrees Fahrenheit and already cooled gas around 18,000 degrees Fahrenheit.

Using the Mid-Infrared Instrument (MIRI) on Webb, researchers obtained detailed spectroscopic data of the cluster’s core, surpassing previous studies that only measured the hottest and coldest gas. Webb’s ability to detect mid-temperature gas provided the first direct evidence of this missing phase in the cooling process.

A key factor in Webb’s detection was its ability to observe neon emission in the mid-infrared. While oxygen, a more prominent indicator of this process, emits in ultraviolet and remains undetectable, the fainter infrared glow of ionized neon allowed researchers to track the cooling gas with Webb’s sensitive instruments.

This discovery serves as a proof of concept for studying other galaxy clusters. While the Phoenix cluster is an extreme case, similar processes may regulate star formation in more typical clusters.

The James Webb Space Telescope, an international collaboration between NASA, ESA (European Space Agency), and CSA (Canadian Space Agency), continues to provide groundbreaking insights into the formation and evolution of galaxies.