JWST shakes up the hunt for earliest galaxy cluster

"The Hubble Space Telescope displayed what the Universe looks like. Its successor, JWST, now reveals how the Universe grew up. Galaxies formed and grew massive swiftly: requiring under 300 million years. Larger-scale, more massive structures, like galaxy clusters, take longer. The earliest mature, fully-fledged cluster is CL J1001+0220. Simulations predict such clusters to appear late: after 2-3 billion years. However, proto-clusters, or still-forming galaxy clusters, appear far earlier."

"A 2019 study revealed protoclusters z66OD and z57OD: with at least 12 and 44 member galaxies, respectively. Then, in 2023, JWST spotted the earliest known protocluster of galaxies assembling: A2744z7p9OD. With seven large, bright member galaxies just 650 million years after the Big Bang, it remains the youngest protocluster identified. However, one hallmark of mature clusters is missing from these protoclusters: hot, X-ray emitting gas."

"However, the discovery of the fourth earliest galaxy protocluster, JADES-ID1, changes all of that. Alongside 66 potential member galaxies, X-ray emitting gas was spotted by NASA's Chandra. It's definitively associated with the distant protocluster, with the right spectrum of X-ray energies. These X-ray emissions mark the earliest cosmic detection of intracluster heating and virialization. Containing trillions of solar masses, such evolved, early protoclusters must be cosmically rare."

Hubble revealed the Universe's appearance while JWST reveals its growth. Galaxies formed and grew massive in under 300 million years, whereas larger structures like galaxy clusters developed more slowly. The earliest mature cluster is CL J1001+0220, with simulations predicting such systems after 2–3 billion years. Proto-clusters appear much earlier: z66OD and z57OD contain at least 12 and 44 members, respectively. JWST found A2744z7p9OD with seven bright members about 650 million years post–Big Bang, but earlier protoclusters lacked hot, X‑ray emitting intracluster gas. JADES‑ID1 contains roughly 66 candidate members and shows Chandra‑detected X‑ray gas, signaling early intracluster heating, virialization, and extreme rarity.

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