In a revelation, the Phoenix galaxy cluster, a gargantuan assembly of gravitationally bound galaxies, defies expectations by churning out stars at a highly vigorous rate, contradicting its anticipated “red and dead” status.
Located 5.8 billion light-years from Earth, this sprawling collection of galaxies is the largest of its kind observed so far, with a central massive galaxy that is surprisingly bright and producing stars at a staggering rate of about 1,000 per year.
The discovery, facilitated by NASA’s James Webb Space Telescope (JWST), has shed light on the mystery of how the Phoenix cluster fuels such rapid star formation, revealing the presence of “warm” gas – a previously unknown intermediate phase between hot and cold gas – that confirms the cluster’s core is actively cooling and generating its stellar fuel.
This finding has significant implications for understanding galaxy evolution, as it suggests that the Phoenix cluster may be undergoing a unique process, potentially shedding light on the formation of stars in other galaxies, and raises questions about whether this phenomenon is an isolated event or a common occurrence in massive galaxy clusters.
In the vast expanse of the universe, a galaxy cluster is so massive that it defies the conventional understanding of star formation. The Phoenix galaxy cluster, located 5.8 billion light years from Earth, has been observed to be producing stars at an unprecedented rate, leaving scientists perplexed about the source of its fuel. Recent research conducted by a team from MIT and other institutions, utilizing NASA‘s James Webb Space Telescope (JWST), has shed new light on this enigma, revealing the presence of warm gas within the cluster’s core.
The Phoenix galaxy cluster was first discovered in 2010 using the South Pole Telescope in Antarctica. It comprises approximately 1,000 galaxies and is named after the constellation in which it resides. Initial observations suggested that the cluster’s central galaxy was undergoing an intense starburst, producing about 1,000 stars per year. This rate is significantly higher than what is typically observed in other galaxy clusters, where the average annual production is around one star.
Star formation is intricately linked to the cooling of interstellar gas. In younger galaxies, this gas cools dramatically, reaching temperatures that allow for star formation. However, in older galaxies like the Phoenix cluster, which should be past its prime star-forming stage, the presence of cold gas poses a puzzle. The question has been whether this cold gas is generated internally within the central galaxy or if it is imported from surrounding galaxies.
To address this question, researchers assumed that if the cold, star-forming gas is indeed coming from within the central galaxy, there should also be gas in a “warm” intermediate phase. This warm gas would serve as evidence that the core of the cluster is the source of the cold stellar fuel. Utilizing JWST’s Mid-Infrared Instrument (MIRI), the team searched for gas with temperatures between 10 kelvins and 1 million kelvins, focusing on a specific wavelength emitted by neon gas at around 300,000 kelvins.
The observations, conducted over 12 hours in July 2023, yielded infrared images that were analyzed to map the locations of warm gas within the central galaxy. The presence of this gas, signified by its emission at a specific wavelength, was observed throughout the field of view, indicating that the central galaxy is undergoing a significant degree of extreme cooling. This cooling process is estimated to generate an amount of ultracold gas each year equivalent to the mass of about 20,000 suns, suggesting that the central galaxy is likely generating its own starburst.
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