The Hubble Space Telescope displayed what the Universe looks like.
Over the course of 50 days, with a total of over 2 million seconds of total observing time (the equivalent of 23 complete days), the Hubble eXtreme Deep Field (XDF) was constructed from a portion of the prior Hubble Ultra Deep Field image. Combining light from ultraviolet through visible light and out to Hubble’s near-infrared limit, the XDF represents humanity’s deepest view of the cosmos: a record that stood until the JWST’s first deep field was released on July 11, 2022.
Credit: NASA, ESA, G. Illingworth, D. Magee, and P. Oesch (University of California, Santa Cruz), R. Bouwens (Leiden University), and the HUDF09 Team
Its successor, JWST, now reveals how the Universe grew up.
This tiny fraction of the JADES survey area, taken with JWST’s NIRCam instrument, showcases relatively nearby galaxies in detail, galaxies at intermediate distances that appear grouped together, and even ultra-distant galaxies that may be interacting or forming stars, despite their faint nature and red appearance. Even though we’ve been performing JWST science for over two years, we are only beginning to probe the full richness of the cosmos with JWST.
Credit: NASA, ESA, CSA, STScI, B. Robertson (UC Santa Cruz), B. Johnson (CfA), S. Tacchella (Cambridge), P. Cargile (CfA)
Galaxies formed and grew massive swiftly: requiring under 300 million years.
This image shows a three-filter NIRCam view of galaxy MoM-z14: the new record holder (as of May 16, 2025) for the most distant galaxy ever discovered. Invisible at wavelengths below 1.8 microns, JWST has measured its spectrum and detected several emission lines, cementing its status as arising from when the Universe was a mere 282 million years old.
Credit: R.P. Naidu et al., Open Journal of Astrophysics (submitted)/arXiv:2505.11263, 2025
Larger-scale, more massive structures, like galaxy clusters, take longer.
This image shows the huge galaxy cluster MACS J1149.5+223, whose light took over 5 billion years to reach us. The huge mass of the cluster is bending the light from more distant objects. The light from these objects has been magnified and distorted due to gravitational lensing. The same effect is creating multiple images of the same distant objects. Meanwhile, the central location of the cluster clearly shows intracluster light: a remarkable tracer of dark matter.
Credit: NASA, ESA, S. Rodney (John Hopkins University, USA) and the FrontierSN team; T. Treu (University of California Los Angeles, USA), P. Kelly (University of California Berkeley, USA) and the GLASS team; J. Lotz (STScI) and the Frontier Fields team; M. Postman (STScI) and the CLASH team; and Z. Levay (STScI)
The earliest mature, fully-fledged cluster is CL J1001+0220.
This X-ray/infrared composite image shows galaxy cluster CL J1001+0220, the earliest known mature, X-ray emitting galaxy cluster. Although this was the earliest known galaxy cluster of any type in 2016, several younger proto-clusters have since been identified. It remains the earliest mature galaxy cluster known today, even in the JWST era.
Credits: X-ray: NASA/CXC/Université Paris/T.Wang et al; Infrared: ESO/UltraVISTA; Radio: ESO/NAOJ/NRAO/ALMA
Simulations predict such clusters to appear late: after 2-3 billion years.
The SIBELIUS project, which simulates galaxies and structures beyond the local Universe, is part of the Virgo Consortium that attempts to use cosmological simulations to reproduce features of galaxies, groups, and clusters that are seen all across the Universe. By using a mix of theory, observations, and simulations, astrophysicists can better understand the nature of dark matter in our cosmos. The formation of large galaxy clusters generally requires long timescales and initially large overdensities, with the largest initial overdensities requiring less time to form clusters.
Credit: Virgo Consortium/SIBELIUS project
However, proto-clusters, or still-forming galaxy clusters, appear far earlier.
These two galaxy protoclusters, z66OD (at a redshift of 6.6) and z57OD (at a redshift of 5.7) are overdense collections of galaxies on large, cluster-like scales, with 12 and 44 galaxies (at least) inside of them, respectively. The blue blobs show the reconstructed mass distribution of these protoclusters, whose light comes from 830 million and 1.0 billion years after the Big Bang.
Credit: Y. Harikane et al., Astrophysical Journal, 2019
A 2019 study revealed protoclusters z66OD and z57OD: with at least 12 and 44 member galaxies, respectively.
This galaxy protocluster, known as z66OD, contains 12 independent galaxies all at the same redshift: z=6.6. Its light comes to us from just 830 million years after the Big Bang. Prior to JWST, this proto-cluster was the earliest collection of galaxies in the same region of space ever known. The blue shading shows the estimated extent of the protocluster.
Credit: NAOJ/Y. Harikane et al., Astrophysical Journal, 2019
Then, in 2023, JWST spotted the earliest known protocluster of galaxies assembling: A2744z7p9OD.
The galaxies that are members of the identified protocluster A2744z7p9OD are shown here, outlined atop their positions in the JWST view of galaxy cluster Abell 2744. At just 650 million years after the Big Bang, it’s the oldest protocluster of galaxies ever identified. This is early, but is consistent with simulations of when the earliest protoclusters should emerge from the most initially overdense regions.
Credit: NASA, ESA, CSA, Takahiro Morishita (IPAC); Processing: Alyssa Pagan (STScI)
With seven large, bright member galaxies just 650 million years after the Big Bang, it remains the youngest protocluster identified.
This image shows the view of JWST’s NIRCam instrument as it looked at galaxy cluster Abell 2744 and revealed a number of galaxies that are members of a proto-cluster. The red squares show several of the galaxies for which spectroscopic measurements were obtained; the orange circles are photometric galaxy candidates that may yet turn out to be part of this cluster. Small, low-mass galaxies form earlier; larger, evolved galaxies and galaxy clusters only appear at later times.
Credit: T. Morishita et al., ApJL, 2023
However, one hallmark of mature clusters is missing from these protoclusters: hot, X-ray emitting gas.
This image composite shows the full-field of a large galaxy cluster within the COSMOS-Web survey, using a combination of JWST NIRCam and Hubble infrared data, with X-ray data from the Chandra X-ray telescope overlaid in violet. The X-rays are evidence from the heated gas that occurs when galaxy clusters merge or experience major disruptive events.
Credit: ESA/Webb, NASA & CSA, G. Gozaliasl, A. Koekemoer, M. Franco, and the COSMOS-Web team
However, the discovery of the fourth earliest galaxy protocluster, JADES-ID1, changes all of that.
A whopping 66 potential member galaxies have been identified in galaxy protocluster JADES-ID1, identified with data obtained with deep JWST imagery. A large overdensity this rare and this early, just 1 billion years after the Big Bang (at z = 5.68), is a remarkable find.
Credit: Á. Bogdán et al., Nature, 2026
Alongside 66 potential member galaxies, X-ray emitting gas was spotted by NASA’s Chandra.
This animation shows a more full field of the early protocluster JADES-ID1 from within the JWST Advanced Deep Extragalactic Survey field. The X-ray data, from NASA’s Chandra X-ray observatory, is overlaid in this animation in blue, showcasing the characteristic X-ray emission of hot gas in galaxy clusters.
Credits: X-ray: NASA/CXC/CfA/Á Bogdán; Infrared: NASA/ESA/CSA/STScI; Image Processing: NASA/CXC/SAO/P. Edmonds and L. Frattare; Animation: E. Siegel
It’s definitively associated with the distant protocluster, with the right spectrum of X-ray energies.
The white contours show higher-energy X-rays, which shouldn’t come from a protocluster, while the yellow contours show the likelihood of low-energy X-rays, which are present, based on the locations of individually identified protocluster members. The violet circle, indicating the central location of the emitted X-rays, is shown superimposed atop the yellow likelihood map.
Credit: Á. Bogdán et al., Nature, 2026
These X-ray emissions mark the earliest cosmic detection of intracluster heating and virialization.
This figure represents an X-ray (from Chandra) and infrared (from JWST) composite of the protocluster of galaxies known as JADES-ID1, the earliest galaxy cluster showing signs of heated, virialized gas that emits low-energy (but not high-energy) X-rays. The Universe, as revealed by this protocluster, can grow up remarkably fast.
Credit: X-ray: NASA/CXC/CfA/Á Bogdán; Infrared: NASA/ESA/CSA/STScI; Image Processing: NASA/CXC/SAO/P. Edmonds and L. Frattare
Containing trillions of solar masses, such evolved, early protoclusters must be cosmically rare.
Here, the El Gordo galaxy cluster is shown in two unusual ways: where the colors represent the mass density of the diffuse mass component as inferred by gravitational lensing data (colors), while the black contours show the X-ray emissions as measured via the Chandra X-ray telescope. Note that the two maps are very different from one another, indicating that overall mass does not follow the same locations that the normal matter does. Late-time galaxy clusters often emit X-rays, but only one early protocluster, JADES-ID1, has been seen to do so thus far.
Credit: J.M. Diego et al. (PEARLS collaboration), A&A, 2023
Mostly Mute Monday tells an astronomical story in images, visuals, and no more than 200 words.