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Something blasted enough energy across the cosmos to tear many of those particles apart again. Astronomers call that event reionization, and for years they\u2019ve debated what caused it.<\/p>\n
A new study points strongly toward one answer: giant newborn star clusters that broke through thick clouds of gas far earlier than expected.<\/p>\n
Researchers used the James Webb Space Telescope alongside the Hubble Space Telescope to study thousands of young star clusters in nearby galaxies.<\/p>\n
The work gave astronomers one of their clearest looks yet at the brief stage after stars are born but still buried inside dense clouds of gas and dust. That hidden phase may have helped reshape the early universe.<\/p>\n
Violent beginnings for young stars<\/p>\n
New stars form when giant clouds of gas collapse under gravity<\/a>. As more stars ignite inside those clouds, the environment turns violent fast. <\/p>\n Massive stars blast out strong stellar winds, ultraviolet radiation, and eventually supernova<\/a> explosions. Those forces shove away the surrounding gas and stop more stars from forming nearby.<\/p>\n Astronomers call this process stellar feedback.<\/p>\n For decades, scientists struggled to figure out exactly how quickly young star clusters clear away those birth clouds. The answer could help explain how galaxies evolve and how the early universe became reionized.<\/p>\n A clue to cosmic reionization<\/p>\n The new research involved an international team led by scientists from Stockholm University and the Oskar Klein Center. University of Massachusetts<\/a> Amherst Distinguished Professor Daniela Calzetti was among the co-authors.<\/p>\n \u201cAs the universe started to cool after the Big Bang, all the electrons and protons that had been scattered everywhere started to find each other and bind together until the universe assumed a neutral charge,\u201d she said.<\/p>\n A massive burst of energy later separated protons and electrons between galaxies in an event known as reionization.<\/p>\n Astronomers have long tried to determine what produced the energy behind that transformation.<\/p>\n Astronomers have long studied nearby star-forming regions inside the Milky Way<\/a>, but Earth\u2019s position inside the galaxy blocks much of the view. Looking at other galaxies gives scientists access to thousands of star clusters at different stages of life.<\/p>\n That became possible thanks to Webb\u2019s infrared instruments, which can see through thick curtains of gas and dust. Hubble added another piece of the puzzle by capturing ultraviolet and visible light.<\/p>\n Together, the telescopes let researchers examine nearly 9,000 star clusters across four nearby galaxies: Messier 51, Messier 83, NGC 628, and NGC 4449.<\/p>\n Some clusters were still deeply buried in gas. Others had partly cleared their surroundings. Some were fully visible.<\/p>\n The team discovered a sharp pattern. Massive star clusters escaped their birth clouds far faster than smaller ones.<\/p>\n The largest clusters broke free after roughly 5 million years. Smaller clusters stayed wrapped in gas for around 7 to 8 million years before emerging.<\/p>\n That gap may sound small, but in astronomy it changes everything.<\/p>\n Why giant star clusters matter<\/p>\n The formation of massive star clusters likely helped drive the reionization of the universe.<\/p>\n The researchers found that the most massive clusters could emerge from their natal clouds in just 5 million years, giving them enough time to produce the photons needed to reionize the universe.<\/p>\n Massive stars naturally pump out huge amounts of ultraviolet radiation<\/a>. If their surrounding gas clears away quickly, that energy can escape into space much sooner.<\/p>\n That could explain how the universe transformed from a dim, neutral place into the bright and structured cosmos seen today.<\/p>\n The findings could also improve computer models of how galaxies evolve.<\/p>\n \u201cSimulations of star formation and stellar feedback have struggled to reproduce how star clusters form and emerge from their natal clouds,\u201d said Angela Adamo, a lead author on the study and principal investigator of FEAST. \u201cThese results give us important new constraints on that process.\u201d<\/p>\n Planet formation under pressure<\/p>\n The findings don\u2019t only affect theories about galaxies. They may also reshape how scientists think about planet formation.<\/p>\n Young stars are often surrounded by spinning disks<\/a> of gas and dust called protoplanetary disks. Those disks eventually build planets.<\/p>\n But if nearby massive stars clear away gas too quickly and flood the area with ultraviolet radiation, planet formation may get interrupted early. That means some star systems could lose the raw material needed to form large planets.<\/p>\n Webb peers into stellar nurseries<\/p>\n \u201cThis work brings together researchers simulating star formation and those working with observations, as well as groups researching planet formation,\u201d said Alex Pedrini.<\/p>\n \u201cUsing Webb, we can look into the cradles of star clusters and connect planet formation to the cycle of star formation and stellar feedback.\u201d<\/p>\n The James Webb Space Telescope was designed to look deep into cosmic history<\/a>, and studies like this show exactly why scientists were so eager to launch it.<\/p>\n Webb is not just spotting distant galaxies. It\u2019s exposing the hidden processes that shaped the universe long before Earth existed.<\/p>\n The full study was published in the journal Nature Astronomy<\/a>.<\/p>\n \u2014\u2013<\/p>\n Like what you read? Subscribe to our newsletter<\/a> for engaging articles, exclusive content, and the latest updates.<\/p>\n Check us out on EarthSnap<\/a>, a free app brought to you by Eric Ralls<\/a> and Earth.com.<\/p>\n \u2014\u2013<\/p>\n","protected":false},"excerpt":{"rendered":"The universe was once dark, hot, and filled with loose particles flying in every direction. Then things cooled…\n","protected":false},"author":2,"featured_media":957600,"comment_status":"","ping_status":"","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[3844],"tags":[70,413,16,15],"class_list":{"0":"post-957599","1":"post","2":"type-post","3":"status-publish","4":"format-standard","5":"has-post-thumbnail","7":"category-space","8":"tag-science","9":"tag-space","10":"tag-uk","11":"tag-united-kingdom"},"share_on_mastodon":{"url":"https:\/\/pubeurope.com\/@uk\/116568712137109027","error":""},"_links":{"self":[{"href":"https:\/\/www.europesays.com\/uk\/wp-json\/wp\/v2\/posts\/957599","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.europesays.com\/uk\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.europesays.com\/uk\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.europesays.com\/uk\/wp-json\/wp\/v2\/users\/2"}],"replies":[{"embeddable":true,"href":"https:\/\/www.europesays.com\/uk\/wp-json\/wp\/v2\/comments?post=957599"}],"version-history":[{"count":0,"href":"https:\/\/www.europesays.com\/uk\/wp-json\/wp\/v2\/posts\/957599\/revisions"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/www.europesays.com\/uk\/wp-json\/wp\/v2\/media\/957600"}],"wp:attachment":[{"href":"https:\/\/www.europesays.com\/uk\/wp-json\/wp\/v2\/media?parent=957599"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.europesays.com\/uk\/wp-json\/wp\/v2\/categories?post=957599"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.europesays.com\/uk\/wp-json\/wp\/v2\/tags?post=957599"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}![\"This](\"https:\/\/www.europesays.com\/uk\/wp-content\/uploads\/2026\/05\/galaxies_m51_m83_ngc-4449_ngc-628_ESA_1s.webp\")
<\/a>This image shows the four galaxies studied in this research, each of which has previously been the subject of an ESA\/Webb Picture of the Month: Messier 51 (top left), Messier 83 (top right), NGC 4449 (bottom left), and NGC 628 (bottom right). Click image to enlarge.Webb and Hubble finally crack the cloud<\/p>\n