Deeper X‑ray and JWST Data Cast Doubt on Claimed Black Hole in Galaxy UHZ1

A new reanalysis of one of the early universe’s most talked-about black hole candidates says the evidence no longer holds up. Using deeper X-ray observations and new infrared limits, astronomers report there is no compelling evidence that the galaxy UHZ1, seen just 470 million years after the Big Bang, hosts the luminous, heavily obscured black hole claimed in 2023.

The new study, “Revisiting the Claim for a Direct-Collapse Black Hole in UHZ1 at z = 10.05,” is led by Fan Zou and has been accepted for publication in The Astrophysical Journal, according to its arXiv record. UHZ1, also known as UNCOVER-26185, has a spectroscopic redshift of 10.054. Zou’s team reanalyzed the full 2.2 million-second Chandra X-ray dataset for the Abell 2744 field, including 0.95 million seconds of previously unpublished observations, and added new JWST mid-infrared photometry at observed wavelengths above 5 microns.

Their central finding is that the supposed hard X-ray signal at UHZ1’s position is weak and unstable. Across plausible ways of reducing the Chandra data, the significance of the 2-7 keV excess comes out to about 2.0 to 2.9 sigma, far below the 4.2 to 4.4 sigma detection reported in the original 2023 study. Zou and colleagues argue that the higher significance depends strongly on a particular astrometric alignment, meaning how the X-ray image is registered to the sky, and is not robustly reproducible. In a Monte Carlo test, they found a 4.2 to 4.4 sigma result appears in 0.1% or less of plausible registration realizations. The new paper also notes that the original claim rested on only about 21 net hard-band counts above a background of about 21.4 counts. If the source were a steady active galactic nucleus, or AGN, its signal should have strengthened as the Chandra exposure grew from 1.25 million seconds to 2.2 million seconds. Instead, the added observations produce a hard-band count rate consistent with zero.

The multiwavelength picture points the same way. UHZ1 is undetected in all nine JWST/MIRI imaging bands examined by Zou’s team. Using the tightest of those upper limits, the authors say any buried AGN must have a bolometric luminosity below 1.3 × 10^45 erg per second. A separate 2026 JWST spectroscopy study led by J. Álvarez-Márquez also found no AGN signatures in the galaxy’s rest-frame ultraviolet-to-optical light. That paper measured a redshift of 10.054 ± 0.011 and described UHZ1 as a low-mass, metal-poor star-forming galaxy with a stellar mass of about 1.7 × 10^8 times that of the sun and a star-formation rate of about 1.3 solar masses per year. As Álvarez-Márquez and colleagues wrote in their abstract, “With no evidence of an active galactic nuclei in the rest-frame UV-to-optical spectrum, UNCOVER-26185 has the properties of a metal-poor, main-sequence star-forming galaxy at redshift 10.”

The original claim came from Akos Bogdán and colleagues in a paper first posted in May 2023 and later accepted in Nature Astronomy. That team interpreted the X-ray excess as a Compton-thick AGN — a black hole shrouded behind extremely dense gas — with an intrinsic 2-10 keV luminosity around 10^46 erg per second, a bolometric luminosity of roughly 5 × 10^45 erg per second, and an inferred black hole mass of about 10^7 to 10^8 solar masses. NASA and the Chandra X-ray Observatory promoted it as “the most distant black hole yet seen in X-rays.” In that 2023 Chandra press release, Bogdán said, “We needed Webb to find this remarkably distant galaxy and Chandra to find its supermassive black hole.” The same release quoted astrophysicist Priyamvada Natarajan saying, “We think that this is the first detection of an ‘Outsize Black Hole’ and the best evidence yet obtained that some black holes form from massive clouds of gas.”

That possibility drew intense attention because a surprisingly massive black hole in such a small, young galaxy would have been an important clue to how the earliest supermassive black holes formed. But the new paper argues that UHZ1 sits in a difficult X-ray environment behind the galaxy cluster Abell 2744, whose hot intracluster gas creates a complex diffuse background that makes faint point-source claims especially sensitive to alignment and background modeling.

The narrower conclusion is not that UHZ1 contains no black hole at all. It is that the evidence for the specific 2023 interpretation — a luminous, heavily obscured AGN and possible direct-collapse black hole at cosmic dawn — is not compelling in the deeper, broader dataset. For now, UHZ1 is best described as a young star-forming galaxy, not a confirmed early quasar.