In the vast expanse of the cosmos, there lies a phenomenon that has baffled astronomers for decades—a galaxy cluster known as the Phoenix cluster, which defies conventional theories of star formation. Located approximately 5.8 billion light-years from Earth, this grouping of galaxies, bound together by gravity, has revealed new insights through the powerful James Webb Space Telescope (JWST).

The Phoenix cluster is unique because, despite hosting a supermassive black hole at its heart, it still manages to form stars at an extraordinary rate. This black hole, with a mass 10 billion times that of the sun, acts as a natural particle accelerator, expelling gas and keeping it hot. According to conventional theories, this should limit star formation, but the Phoenix cluster continues to produce stars in defiance of these principles.

This paradox has vexed scientists, turning the Phoenix cluster into a cosmic enigma. Recent investigations by JWST, building on a decade of previous research using the Hubble Space Telescope, Chandra X-Ray Observatory, and various ground-based observatories, may finally unravel this mystery.

Lead investigator Michael McDonald from the Massachusetts Institute of Technology (MIT) in Cambridge compared the cooling process in the Phoenix cluster to a ski slope. He said,

“We can compare our previous research about the Phoenix cluster, which found a different cooling rate at different temperatures, with ski slopes. The Phoenix cluster has the biggest hot gas reservoir and cooler from each galaxy cluster – analog with the removal of the busiest seats, bringing the most ski players to the top of the mountain. However, not all ski players descend to the mountain, which means not all gas cools to low temperatures.”.

– Michael McDonald

When comparing this scenario to a ski resort, he added, “If you have a skiing slope where there are more people who come out of the skiing elevator at the top than those who arrive at the bottom, it will be a problem!

The team believed that JWST finally discovered “the missing skier,” a cooling gas trapped in the intermediary temperature range of the Phoenix cluster’s “Mountain.”

‘Lost Skiers’ on the Slopes of the Phoenix Cluster

The team utilized the Mid-InfraRed Instrument (Miri) on JWST to collect 2D spectroscopy data from the region of the sky containing the Phoenix cluster. This allowed them to study the core of this galaxy grouping in unprecedented detail, uncovering the so-called “lost” cooling gas, which is crucial for star formation.

They identified hot gas reaching temperatures around 18,000 degrees Fahrenheit (10,000 degrees Celsius) alongside cooler gas around 540,000 degrees Fahrenheit (300,000 degrees Celsius) located within cavities in the Phoenix cluster, much like differences in the circulation of fluids on Earth’s surface.

McDonald explained, “Previous studies only measured gas at the extremes of the temperature distribution within the cluster. We were limited and unable to detect the “warm” gas we were searching for. With JWST, we can do this for the first time.”

The sensitivity of the infrared observations from JWST received a boost from a natural phenomenon in the Phoenix cluster where neon atoms and oxygen, ionized or stripped of electrons, were found in the same environment.

While oxygen is brighter, it is only visible in the ultraviolet light wavelength. Neon, while dimmer, emits infrared light, which JWST is specifically designed to detect.

“The middle wavelength of the infrared detected by JWST is causing a neon Vl signature to become really prominent,” MIT researcher Michael Reefe notes. “Although this emission is usually more difficult to detect, JWST’s sensitivity eliminates noise at the mid-infrared levels.”

Although the Phoenix cluster stands out for its unique properties, the team aims to apply this “Proof of Concept” technique and Miri’s sensitivity to study other galaxy clusters, expanding our understanding of these cosmic phenomena.