Astrophysicists working with the JWST have found a surprising amount of metal in a galaxy only 350 million years after the Big Bang. How does that fit in with our understanding of the Universe?<\/p>\n
<\/p>\n The origin of the Universe\u2019s first metals is a foundational question in astrophysics. Shortly after the Big Bang, the Universe was made up almost entirely of hydrogen, the simplest of the elements. There was a little helium, even less lithium, and possibly an infinitesimal amount of beryllium. When you look at the periodic table of the elements, those are the first four. <\/p>\n In astronomy, all the elements heavier than hydrogen and helium are called metals. Metals are produced in stars and nowhere else (except for the tiny amount produced by the Big Bang itself.) Tracing the formation of the Universe\u2019s metals from the Big Bang to now is one of astrophysics\u2019 fundamental quests. <\/p>\n Metallicity is a fundamental concept in our study of the Universe. Without metals, rocky planets can\u2019t form. Neither can life. Over successive generations of stars, the Universe\u2019s metallicity has increased. So there\u2019s an underlying trajectory that stems from the first metals and leads directly to us. <\/p>\n The study of ancient galaxies is one of the James Webb Space Telescope\u2019s primary quests. The JWST Advanced Deep Extragalactic Survey\u00a0(JADES) examined a region of the sky looking for faint, early galaxies. By looking so far back in time to the Universe\u2019s early galaxies, the JWST is shedding light on ancient metallicity. <\/p>\n A team of researchers working with JADES observations examined a galaxy only 350 million years after the Big Bang and found carbon. They may have also found oxygen and neon, all metals in astronomy. Their findings are in a new paper titled \u201cJADES: Carbon enrichment 350 Myr after the Big Bang in a gas-rich galaxy.\u201d The lead author is Francesco D\u2019Eugenio, a post-doc astrophysicist at the Kavli Institute for Cosmology at Cambridge. <\/p>\n The first stars that formed in the Universe are called Population III stars. They\u2019re the most ancient stars, and they were massive, luminous, and hot, with almost no metals. The tiny amount of metals they held came from the first supernovae among their numbers. <\/p>\n Much of our knowledge about Population III stars is theoretical because these ancient stars, in their ancient galaxies, are extremely difficult to observe. But the JWST is capable of it. It can\u2019t individual stars, but its powerful NIRSpec instrument can detect different elements in the galaxy by their telltale light signatures. <\/p>\n This new research is based on a galaxy at z=12.5 near the Cosmic Dawn, a critical era in the Universe\u2019s history. When the researchers studied the JWST\u2019s observations, they discovered an unexpected amount of carbon in the galaxy. It\u2019s either in the interstellar medium (ISM) or the circumgalactic medium (CGM.) \u201cThis is the most distant detection of a metal transition and the most distant redshift determination via emission lines,\u201d they explain. It\u2019s also the \u201cmost distant evidence of chemical enrichment\u201d found to date.<\/p>\n This detection directly collides with our understanding of metal-free population III stars. \u201cThe detection of C iii\u2013 and its high EW (equivalent widths<\/em>)\u2013 rules out scenarios of pristine stellar populations,\u201d the authors write.<\/p>\n If Webb has ruled out the existence of pristine, metal-free population III stars, that\u2019s big news. It\u2019s another instance of the powerful space telescope upending our best explanations for the Universe we see around us. But it\u2019s not entirely shocking; the existence of population III stars is theoretical. Considering everything else we know about the Universe, their existence made sense.<\/p>\n But population III stars were never a certainty.<\/p>\n When something like this is discovered, scientists take pains to consider every other possible explanation for what they\u2019re seeing. <\/p>\n Are they really seeing carbon in the stars in this distant, ancient galaxy? Or could something else be behind these emissions? The ancient galaxy has more in it than just stars. It\u2019s also home to a supermassive black hole (SMBH.) When an SMBH feeds on matter, it can flare brightly as an active galactic nuclei (AGN.) That light signal could be what the JWST is seeing. <\/p>\n \u201cMoreover, a supermassive accreting black hole has been identified in this galaxy, suggesting that the peculiar chemical abundances might be primarily associated with its nuclear region,\u201d the researchers explain. <\/p>\n There\u2019s another potential source of carbon in the galaxy. They\u2019re AGB stars\u2014asymptotic giant branch stars. AGB stars aren\u2019t large explosive stars like supernovae progenitors are, but they\u2019re large stars that have left the main sequence. Compared to supernovae, AGB stars produce metals gently. <\/p>\n But takes a long time for a star to evolve into an AGB star. When the Universe was only 350 million years old, no stars had lived long enough to become AGBs. \u201c\u2026AGB stars cannot contribute to carbon enrichment at these early epochs,\u201d the authors write.<\/p>\n In the end, the researchers report the detection of carbon, but they can\u2019t tell us exactly where it came from. They may be \u201c\u2026 the heritage of the first generation of supernovae from Population III progenitors,\u201d they write. <\/p>\n The JWST was pushed to its limits to see this early galaxy. \u201cThis detection of the most distant metal transition, which has provided such precious information about the earliest phases of the chemical enrichment, has required a very long exposure,\u201d the authors explain. It took 65 hours of JWST time to gather this data due to the galaxy\u2019s extreme faintness. <\/p>\n Even with all that observing time, the researchers can only arrive at tentative explanations for the metallicity they see. It\u2019s not very practical to use 65 hours of JWST time to study a galaxy spectroscopically, but that\u2019s what the JWST needs to do for this kind of precise spectroscopy. That may change in the future. <\/p>\n \u201cHowever, in the future, large-area surveys and gravitational lenses may help identify more high-redshift galaxies that are sufficiently bright for deep spectroscopic follow-up with shorter exposures,\u201d the researchers write.<\/p>\n When and if that happens, astrophysicists will have the much sought-after larger sample size. With that valuable data in hand, maybe they can arrive at a firmer explanation for this surprising find. <\/p>\n![\"Artist's](\"https:\/\/www.universetoday.com\/wp-content\/uploads\/2010\/06\/NASA-WMAP-first-stars.jpg\")
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