An X-ray-emitting protocluster at z ≈ 5.7 reveals rapid structure growth.
basic_science · Level V
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- Record sourced from PubMed, PMID 41606151.
- Also identified by DOI 10.1038/s41586-025-09973-1 and PMC identifier 12851925.
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Abstract
Galaxy clusters are the most massive gravitationally bound structures in the universe and serve as tracers of the assembly of large-scale structure<sup>1</sup>. Studying their progenitors, protoclusters, sheds light on the earliest stages of cluster formation. However, detecting protoclusters is demanding: their member galaxies are loosely bound and the emerging hot intracluster medium (ICM) may only be in the initial stages of virialization<sup>2-4</sup>. Recent James Webb Space Telescope (JWST) observations located several protocluster candidates by identifying overdensities of z ≳ 5 galaxies<sup>5-9</sup>. However, none of these candidates was detected by X-ray observations, which offer a powerful way to unveil the hot ICM. Here we report the combined Chandra and JWST detection of a protocluster, JADES-ID1, at z ≈ 5.68, merely one billion years after the Big Bang. We measure a bolometric X-ray luminosity of <math xmlns="http://www.w3.org/1998/Math/MathML"> <msub><mrow><mi>L</mi></mrow> <mrow> <mrow><mrow><mi>bol</mi></mrow> </mrow> </mrow> </msub> <mo>=</mo> <mrow><mo>(</mo> <mrow><mn>1.</mn> <msubsup><mrow><mn>5</mn></mrow> <mrow><mo>-</mo> <mn>0.6</mn></mrow> <mrow><mo>+</mo> <mn>0.5</mn></mrow> </msubsup> </mrow> <mo>)</mo></mrow> <mo>×</mo> <mn>1</mn> <msup><mrow><mn>0</mn></mrow> <mrow><mn>44</mn></mrow> </msup> <mspace></mspace> <mrow><mrow><mi>erg</mi></mrow> </mrow> <mspace></mspace> <msup> <mrow> <mrow><mrow><mi>s</mi></mrow> </mrow> </mrow> <mrow><mo>-</mo> <mn>1</mn></mrow> </msup> </math> and infer a total gravitating mass of <math xmlns="http://www.w3.org/1998/Math/MathML"> <msub><mrow><mi>M</mi></mrow> <mrow><mn>500</mn></mrow> </msub> <mo>=</mo> <mrow><mo>(</mo> <mrow><mn>1.</mn> <msubsup><mrow><mn>8</mn></mrow> <mrow><mo>-</mo> <mn>0.7</mn></mrow> <mrow><mo>+</mo> <mn>0.6</mn></mrow> </msubsup> </mrow> <mo>)</mo></mrow> <mo>×</mo> <mn>1</mn> <msup><mrow><mn>0</mn></mrow> <mrow><mn>13</mn></mrow> </msup> <mspace></mspace> <msub><mrow><mi>M</mi></mrow> <mrow><mo>⊙</mo></mrow> </msub> </math> , making this system a progenitor of today's most massive galaxy clusters. The detection of extended, shock-heated gas indicates that substantial ICM heating can occur in massive halos as early as z ≈ 5.7. Also, given the limited survey volume, the discovery of such a massive cluster is statistically unlikely<sup>10</sup>, implying that the formation of the large-scale structure must have occurred more rapidly in some regions of the early universe than standard cosmological models predict.