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\t\t\t\t\t\t16\/06\/2026<\/span> Researchers have confirmed a new class of objects within our Milky Way galaxy: survivors called ‘bulge fossil fragments.’ Terzan 5 is the prototype of these remnants of our galaxy’s early formation. Using the NASA\/ESA\/CSA James Webb Space Telescope and the NASA\/ESA Hubble Space Telescopes researchers have shown that Terzan 5 is not a globular star cluster as it was once classified. Instead, it is something much odder and rarer.\u00a0<\/p>\n<\/div>\n The cluster contains four separate generations of stars, confirming it as the prototype of a ‘bulge fossil fragment’.\u00a0Billions of years ago, similar primordial clumps spread out and merged to form the Milky Way\u2019s bulge, yet Terzan 5 remained intact until the present day. \u00a0<\/p>\n The new study that combined recent observations from Webb with data taken over 12 years from Hubble has shown that Terzan 5 experienced up to four distinct episodes of star formation, confirming that it\u2019s not a true globular cluster.<\/p>\n A globular star cluster typically has only one ancient star population. New data not only confirms the existence of two distinct populations of stars in Terzan 5, but also provides evidence for two more recent rounds of star formation. Although located within the crowded bulge of the Milky Way galaxy, our galaxy\u2019s central, spherical region of older stars, Terzan 5 was massive enough to maintain its separate identity while lighter weight systems spread out and mixed to form the bulge billions of years ago. It\u2019s like a lump in an otherwise well-mixed cake batter.<\/p>\n \u201cWebb\u2019s new near-infrared observations, cross-referenced with Hubble\u2019s archival observations, have given us a much clearer picture of the history of Terzan 5,\u201d<\/i>\u00a0said Giorgia Zullo, who led the research and is a PhD student at the University of Bologna in Italy.<\/p>\n These results were presented at a press conference Tuesday at the 248th meeting of the American Astronomical Society, and were published in\u00a0Astronomy & Astrophysics.<\/i><\/p>\n<\/p><\/div>\n Discovered in 1968 by astronomer Azop Terzan, Terzan 5 resembles a globular cluster in many ways. However, in 2009 this system was discovered to harbor two distinct populations of stars. In 2016 Hubble provided the first estimate of their ages, showing that one formed roughly 12 billion years ago (as the Milky Way itself was assembling) and the other about 5 billion years ago, just before Earth started forming. This pointed to a more complex history than a typical globular cluster.<\/p>\n Studying Terzan 5 is complicated by its location in a region of our galaxy crowded with stars and heavily obscured by dust. This is where Webb stepped in. Its infrared view allowed the research team to peer through the dust and catalog many more stars, and fainter stars, than previous work. By measuring star colours and brightnesses, astronomers can classify them into populations of different ages and chemistries.<\/p>\n Webb was able to measure these key properties for every star within the field of view in the sky\u00a0\u2013\u00a0both stars within Terzan 5 and unrelated foreground stars. To isolate the stars of Terzan 5, the team relied on the power and longevity of Hubble. The 12-year separation of Hubble\u2019s exposures allowed the team to measure very small movements of individual stars, known as proper motions, to determine which stars belong to Terzan 5 and which are part of the Milky Way galaxy\u2019s bulge.<\/p>\n By combining data from both Webb and Hubble, the researchers found strong evidence for two more stellar populations, one that formed 3.8 billion years ago and another only 2.5 billion years ago. They also were able to determine the ages of the previously known stellar populations with unprecedented precision, finding that they formed 12.5 billion and 4.7 billion years ago.<\/p>\n With the previously known two generations of stars, astronomers could not rule out the possibility that Terzan 5 interacted with another object, like a globular cluster or a giant molecular cloud, becoming enriched with new gas and dust that set off a second round of star formation. With four stellar generations, those explanations are ruled out.<\/p>\n Measurements of the stellar composition of Terzan 5 populations made at the W. M. Keck Observatory and European Southern Observatory\u2019s Very Large Telescope also point toward very distinct populations.\u00a0\u201cAlong with the ages of these populations, the cluster preserves a fossil record of progressive enrichment of heavy elements by supernovae,\u201d<\/i>\u00a0said co-author R. Michael Rich, a research astronomer at the University of California, Los Angeles.<\/p>\n Terzan 5 formed multiple generations of stars because it was able to retain the necessary raw materials. There is evidence of powerful\u00a0supernova\u00a0explosions in Terzan 5 that forged heavier elements that were swept up by subsequent generations of stars. In lighter weight systems, the force of the explosions themselves could have ejected the resulting elements as well as sweeping out leftover gas and dust. The progenitor of Terzan 5 had enough mass to retain those stars\u2019 ejections, allowing new generations of stars to form over billions of years.<\/p>\n<\/p><\/div>\n The results show that Terzan 5 is most likely the remnant of a much more massive stellar system that initially formed 12.5 billion years ago. Terzan 5 is extraordinary because it survived\u00a0\u2013 and never merged or fully ‘mixed in’ with the Milky Way galaxy\u2019s bulge.\u00a0\u201cFor some reason, this peculiar clump of stars formed separately from the bulge and was not destroyed as the bulge itself formed,\u201d<\/i>\u00a0said Francesco R. Ferraro, a professor at the University of Bologna and principal investigator of the Webb observations.\u00a0\u201cTerzan 5 is what we now call a bulge fossil fragment because it resembles the primordial clumps that contributed to the formation of the bulge.\u201d<\/i><\/p>\n To date, there\u2019s one other known cosmic object like Terzan 5.\u00a0Liller 1\u00a0was the second to be reclassified from a globular star cluster to a bulge fossil fragment. It also contains multiple generations of stars. There may be more objects like it. Between 40 to 50 additional globular clusters that orbit within the bulge will be examined by Ferraro\u2019s team to determine if their stellar populations are all the same, like globular clusters, or have several generations, like bulge fossil fragments.\u00a0<\/p>\n<\/p><\/div>\n Ultimately, this research may improve what we know about how the central bulges of galaxies form over hundreds of millions of years.\u00a0\u201cBased on observations and in-depth simulations, we think that galaxies in the early Universe had huge disks of gas that fragmented into clumps and formed stars. These clumps migrated to the centre of the galaxies, and many merged to form their bulges,\u201d\u00a0<\/i>said Barbara Lanzoni, a co-author and associate professor at the University of Bologna. For example, Webb has turned up several examples of \u201cclumpy\u201d galaxies that were actively forming when the Universe was only a few hundred million years old, like the clumps in the\u00a0Firefly Sparkle galaxy.\u00a0\u201cTerzan 5 may provide direct evidence that can help explain how bulges formed in galaxies throughout the Universe,\u201d<\/i>\u00a0Barbara\u00a0said.<\/p>\n<\/p><\/div>\n \nMore information<\/b> Webb is an international partnership between NASA, ESA and the Canadian Space Agency (CSA).<\/p>\n Release on esawebb.org<\/p>\n Science paper<\/p>\n Release on NASA website<\/p>\n \u00a0<\/p>\n \nContact:<\/b>
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\n\t\t\t\t\t\t\t\t<\/figcaption><\/figure>\nFour generations of stars<\/h2>\n
\u2018Bulge fossil fragment\u2019<\/h2>\n
Potential parallels for galaxy formation near, far<\/h2>\n
Webb\u00a0is the largest, most powerful telescope ever launched into space. Under an international collaboration agreement, ESA provided the telescope\u2019s launch service, using the Ariane 5 launch vehicle. Working with partners, ESA was responsible for the development and qualification of Ariane 5 adaptations for the Webb mission and for the procurement of the launch service by Arianespace. ESA also provided the workhorse spectrograph\u00a0NIRSpec\u00a0and 50% of the mid-infrared instrument\u00a0MIRI, which was designed and built by a consortium of nationally funded European Institutes (The MIRI European Consortium) in partnership with JPL and the University of Arizona.<\/p>\n
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