heic2609 \u2014 Science Release<\/p>\n
Researchers show that a galaxy\u2019s young, tightly packed stars converted nearby gas from opaque to clear only 1.4 billion years after the Big Bang<\/p>\n
23 June 2026<\/p>\n
Astronomers using the NASA\/ESA Hubble Space Telescope have found something they never expected: ultraviolet light from a galaxy that existed just 1.4 billion years after the Big Bang. That galaxy contains tightly clustered young stars that produce ionising light capable of transforming the opaque, neutral gas within and immediately around the galaxy, clearing our view. This suggests that similar galaxies in the early Universe were responsible for clearing the neutral fog of hydrogen gas that once filled the cosmos.<\/p>\n
The galaxy, cataloged MXDFz4.4, existed at the end of the era of reionisation<\/a>, a transformative period in our Universe. During roughly the first billion years of the cosmos, the gas between stars and galaxies was opaque to energetic ultraviolet light. As time wore on, gas everywhere became transparent or ionised. The changeover was not like an on\/off switch, but likely took hundreds of millions of years. Researchers are still collecting evidence to fully understand how this happened, which is why MXDFz4.4 sets a critical precedent.<\/p>\n A paper describing this discovery was published<\/a> 23 June 2026 in the Astrophysical Journal.<\/p>\n \u201cObserving a galaxy like this was thought to be impossible,\u201d said lead author Ilias Goovaerts, a postdoctoral fellow at the Space Telescope Science Institute (STScI) in Baltimore. \u201cResearchers expected the \u2018fog\u2019 or neutral hydrogen that filled the early Universe would be too thick and obscure our view of its ionising light. Hubble not only spotted that light, but it also helped reveal incredible details about the galaxy\u2019s characteristics.\u201d<\/p>\n Great light \u2018escape\u2019<\/p>\n Young, massive stars emit ultraviolet light capable of ionising hydrogen atoms. As this light traveled for over 12 billion years to reach Hubble, space expanded, and the light stretched or redshifted [1]<\/a> into visible light. Hubble\u2019s wavelength coverage, combined with the sensitivity and resolution of its space-based vantage point, makes it the only telescope capable of capturing this ultraviolet light from the early Universe.<\/p>\n \u201cAstronomers have found many galaxies that existed at this point in the history of the Universe, but we haven\u2019t detected ionising photons [2]<\/a> from any of them, making MXDFz4.4 one of a kind,\u201d said Marc Rafelski, a co-author and Hubble deputy mission head at STScI.<\/p>\n Hubble\u2019s long exposures, pulled from several existing surveys, revealed that the galaxy\u2019s young, massive stars are the source of the ultraviolet light, which cleared the surrounding space. These stars formed in bursts within the last few million years of MXDFz4.4\u2019s existence and are crammed together.<\/p>\n Amplifying this crowding effect, MXDFz4.4 is about 100 times smaller than our Milky Way galaxy, but is forming stars 10 times faster.<\/p>\n \u201cA lot of young, hot, massive stars in a small space do a better job of blasting through opaque gas,\u201d Goovaerts said. The researchers estimate that 50 to 100% of the young stars\u2019 energetic ionising light is escaping the surrounding gas.<\/p>\n Massive stars\u2019 lifetimes also play a role, since they live for only a few million years. Many explode as supernovae<\/a>, releasing gigantic amounts of energy and blowing colossal holes that allow even more light to escape.<\/p>\n Partnering with other observatories<\/p>\n Hubble could not do this alone. These conclusions are supported by survey data taken by the NASA\/ESA\/CSA James Webb Space Telescope<\/a> in near-infrared light and the MUSE eXtremely Deep Field or MXDF, the galaxy\u2019s namesake, captured by the European Southern Observatory\u2019s Very Large Telescope (VLT) in visible light.<\/p>\n The team used Webb\u2019s data to determine the galaxy\u2019s mass, analyse its older stars, and measure the galaxy\u2019s star formation history. The galaxy\u2019s older stars are less massive and cooler, and therefore not responsible for changing the gas around them.<\/p>\n Comparing Hubble and Webb data also showed that recent star formation happened in bursts.\u00a0Data from the VLT also pinpointed when MXDFz4.4 existed: 1.4 billion years after the Big Bang. Before this discovery, researchers had only identified a galaxy emitting ionised light from a time when the Universe was 1.6 billion years old. Only a few additional examples have been identified, and those existed when the Universe was about 2 billion years old. MXDFz4.4 brings researchers closer to drawing firm conclusions about how the Era of Reionisation unfolded.<\/p>\n “These insights into MXDFz4.4 were possible thanks to the powerful combination of Hubble, Webb and the VLT,” said co-author Alexander Beckett, a postdoctoral fellow at the Laboratoire d’Astrophysique de Marseille. “Even then, only using state-of-the-art analysis software, that was primarily developed in Marseille, were we able to measure the properties of this remarkable galaxy.”<\/p>\n Expanding what we know<\/p>\n Studying the Era of Reionisation is a decades-old endeavour. Researchers use statistics about star populations in nearby galaxies, which we can observe in great detail, to make well-informed assumptions about what might be happening in galaxies in the early Universe, in part because their star populations are too distant to resolve in any detail<\/a>.<\/p>\n In 2023, researchers using Webb<\/a> showed that galaxies\u2019 stars emitted enough light to heat and ionise the gas around them 900 million years after the Big Bang. This was a breakthrough, but astronomers need galaxies like MXDFz4.4 to fully explain how the process happened, since it shows how the high-energy light from young stars managed to escape the gas and dust within the galaxy itself.<\/p>\n It\u2019s possible other galaxies like MXDFz4.4 are waiting to be discovered.<\/p>\n \u201cHubble\u2019s observations of MXDFz4.4 let us test our hypotheses much closer to the Era of Reionisation than ever before,\u201d Rafelski said. \u201cFinding more galaxies, especially at slightly later cosmic times where larger samples are within reach, would let us refine these measurements and figure out what cleared our view as that era was ending.\u201d<\/p>\n Notes<\/p>\n [1] As light travels from great distances to Hubble’s mirrors, it is stretched to longer and longer red wavelengths, or cosmologically redshifted, as the Universe expands. Astronomers can look for known features in an object’s spectrum<\/a> to see if they are shifted from their normal position on the spectrum. The difference between their normal position and their new position is called their cosmological redshift. Since space and time are interlinked, distant objects with increasing redshift are further back in time because it takes their light so long to reach us. Along with measuring the expansion of the Universe, Hubble can employ its detectors to receive light from early galaxies billions of years ago.<\/p>\n [2] A photon is an elementary particle representing the smallest amount (a quantum) of light and the carrier (gauge boson) of the electromagnetic force. Photons have zero rest mass, no electrical charge, always travel in a vacuum at the speed of light, and carry energy equal to their radiation frequency multiplied by Planck’s constant.<\/p>\n More information<\/p>\n The Hubble Space Telescope is a project of international cooperation between ESA and NASA.<\/p>\n Image Credit: NASA, ESA, STScI, I. Goovaerts, M. Rafelski, A. Koekemoer (STScI). Image Processing: A. Pagan (STScI)<\/p>\n Links<\/p>\n Contacts<\/p>\n \n Bethany Downer \n ESA Newsroom and Media Relations Office
ESA\/Hubble Chief Science Communications Officer
Email: [email\u00a0protected]<\/a><\/p>\n
Email: [email\u00a0protected]<\/a><\/p>\n