Numerous bow shocks in the outer Helix Nebula reveal mixing of AGB shell fragments into the interstellar medium

Numerous bow shocks in the outer Helix Nebula reveal mixing of AGB shell fragments into the interstellar medium | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Physical Sciences - Article Numerous bow shocks in the outer Helix Nebula reveal mixing of AGB shell fragments into the interstellar medium Pieter van Dokkum, Roberto Abraham, William Bowman, Seery Chen, and 4 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-8693689/v1 This work is licensed under a CC BY 4.0 License Status: Under Review Version 1 posted You are reading this latest preprint version Abstract Near the end of their lives, low- and intermediate-mass stars expel metal-enriched envelopes on the asymptotic giant branch (AGB), ultimately producing planetary nebulae (PNe).1,2 This ejected material is expected to fragment and mix into the interstellar medium (ISM), but this final assimilation step has been difficult to observe directly.3,4 Here we report evidence for this process in the form of twenty-two bow shocks in the eastern outskirts of the Helix Nebula, detected in Hα emission with the partially completed MOTHRA telescope. Unlike the large-scale wind–ISM bow shocks commonly observed around evolved stars,5–7 the shocks are compact and associated with individual AGB shell fragments. Going outward from the central star, the characteristic stand-off distance R0 decreases by a factor of ≈30 over the radial range r = 0.4–1.4 pc. This is accompanied by a morphological transition from thin, Wilkin-like bows8 with no detected obstacle at the origin to fuzzy, patchy structures. We interpret this progression as the erosion and shredding of initially intact fragments. The slope of the observed R0–r relation implies fragment destruction on a timescale of ≈ 10^4 yr, providing a rare direct constraint on the time-scale for disruption and entrainment of fragmented stellar ejecta into the ISM.9 Physical sciences/Astronomy and planetary science/Astronomy and astrophysics/Stellar evolution Physical sciences/Astronomy and planetary science/Astronomy and astrophysics/Interstellar medium Full Text Additional Declarations There is NO Competing Interest. Cite Share Download PDF Status: Under Review Version 1 posted You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. Our growing team is made up of researchers and industry professionals working together to solve the most critical problems facing scientific publishing. Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-8693689","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Physical Sciences - Article","associatedPublications":[],"authors":[{"id":589715192,"identity":"2276907f-555f-4510-a31b-f54c7d88c233","order_by":0,"name":"Pieter van Dokkum","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAABD0lEQVRIiWNgGAWjYDACZgTTgLHhAAMDPwMDI5BiYGzArQUuB9EiCeTi18KArsXgAAEt5uzMxx983MOQ2D+7eePDGWcORxvfSH5w4AODjeyGA9i1WDazJTbOeMaQOOPOsWLDDTcO5267kWZwcAZDmjEuLQaHeQybeQ4wGDPcyDGTfPABpCUBKMhwOBG3Fv6PzX+AWuRhWjbPSP9w+A/DfzxaeBibgd6VMwBpATlsg0SOwWFgCODUAvSL4cyeAxJyhjfSig1nnEnPnXHmTcHBHoNk45k4tJjzH37w4ccBGx65G8kbH/Ycs87tb0/f+OBHhZ1sHy6HQSgJJCGBBIQ4Hi3IgB+H6aNgFIyCUTBiAQA/ynDItHCJdgAAAABJRU5ErkJggg==","orcid":"https://orcid.org/0000-0002-8282-9888","institution":"Yale University","correspondingAuthor":true,"prefix":"","firstName":"Pieter","middleName":"van","lastName":"Dokkum","suffix":""},{"id":589715193,"identity":"97ca240f-7598-42ea-bf31-c0a96c4ca32b","order_by":1,"name":"Roberto Abraham","email":"","orcid":"","institution":"Dragonfly Focused Research Organization","correspondingAuthor":false,"prefix":"","firstName":"Roberto","middleName":"","lastName":"Abraham","suffix":""},{"id":589715194,"identity":"a8703f0d-0327-4a27-ba90-6831648b7e9c","order_by":2,"name":"William Bowman","email":"","orcid":"https://orcid.org/0000-0003-4381-5245","institution":"Dragonfly Focused Research Organization","correspondingAuthor":false,"prefix":"","firstName":"William","middleName":"","lastName":"Bowman","suffix":""},{"id":589715195,"identity":"db2d431a-0a3a-492b-a4b7-5c195450409e","order_by":3,"name":"Seery Chen","email":"","orcid":"","institution":"Dragonfly Focused Research Organization","correspondingAuthor":false,"prefix":"","firstName":"Seery","middleName":"","lastName":"Chen","suffix":""},{"id":589715196,"identity":"07518dae-5297-4231-9d46-53bd65a8fa14","order_by":4,"name":"Steven Janssens","email":"","orcid":"https://orcid.org/0000-0003-0327-3322","institution":"Dragonfly Focused Research Organization","correspondingAuthor":false,"prefix":"","firstName":"Steven","middleName":"","lastName":"Janssens","suffix":""},{"id":589715197,"identity":"30bbf93e-1c92-41d4-ac78-a1cc1571a5e4","order_by":5,"name":"Deborah Lokhorst","email":"","orcid":"https://orcid.org/0000-0002-2406-7344","institution":"National Research Council Canada","correspondingAuthor":false,"prefix":"","firstName":"Deborah","middleName":"","lastName":"Lokhorst","suffix":""},{"id":589715198,"identity":"1407f008-7bf4-4f83-813b-1caf515bee17","order_by":6,"name":"Imad Pasha","email":"","orcid":"","institution":"Dragonfly Focused Research Organization","correspondingAuthor":false,"prefix":"","firstName":"Imad","middleName":"","lastName":"Pasha","suffix":""},{"id":589715199,"identity":"43ac093c-f020-49ff-8d09-b9d14f155425","order_by":7,"name":"Carter Rhea","email":"","orcid":"","institution":"Dragonfly Focused Research Organization","correspondingAuthor":false,"prefix":"","firstName":"Carter","middleName":"","lastName":"Rhea","suffix":""}],"badges":[],"createdAt":"2026-01-25 16:20:07","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-8693689/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-8693689/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":102746354,"identity":"1e29447f-92d9-427b-8223-5b59839ddcee","added_by":"auto","created_at":"2026-02-16 08:56:58","extension":"pdf","order_by":1,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":2781344,"visible":true,"origin":"","legend":"Article File","description":"","filename":"helixsubmission.pdf","url":"https://assets-eu.researchsquare.com/files/rs-8693689/v1_covered_177d85c1-2bc4-4b5a-958a-7e0808aa85b1.pdf"}],"financialInterests":"There is \u003cb\u003eNO\u003c/b\u003e Competing Interest.","formattedTitle":"Numerous bow shocks in the outer Helix Nebula reveal mixing of AGB shell fragments into the interstellar medium","fulltext":[],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":false,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":true,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":true,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":true,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"nature-portfolio","isNatureJournal":true,"hasQc":false,"allowDirectSubmit":false,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"","title":"Nature Portfolio","twitterHandle":"","acdcEnabled":false,"dfaEnabled":false,"editorialSystem":"ejp","reportingPortfolio":"","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"","lastPublishedDoi":"10.21203/rs.3.rs-8693689/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-8693689/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"Near the end of their lives, low- and intermediate-mass stars expel metal-enriched envelopes on the asymptotic giant branch (AGB), ultimately producing planetary nebulae (PNe).1,2 This ejected material is expected to fragment and mix into the interstellar medium (ISM), but this final assimilation step has been difficult to observe directly.3,4 Here we report evidence for this process in the form of twenty-two bow shocks in the eastern outskirts of the Helix Nebula, detected in Hα emission with the partially completed MOTHRA telescope. Unlike the large-scale wind–ISM bow shocks commonly observed around evolved stars,5–7 the shocks are compact and associated with individual AGB shell fragments. Going outward from the central star, the characteristic stand-off distance R0 decreases by a factor of ≈30 over the radial range r = 0.4–1.4 pc. This is accompanied by a morphological transition from thin, Wilkin-like bows8 with no detected obstacle at the origin to fuzzy, patchy structures. We interpret this progression as the erosion and shredding of initially intact fragments. The slope of the observed R0–r relation implies fragment destruction on a timescale of ≈ 10^4 yr, providing a rare direct constraint on the time-scale for disruption and entrainment of fragmented stellar ejecta into the ISM.9","manuscriptTitle":"Numerous bow shocks in the outer Helix Nebula reveal mixing of AGB shell fragments into the interstellar medium","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2026-02-12 04:10:54","doi":"10.21203/rs.3.rs-8693689/v1","editorialEvents":[],"status":"published","journal":{"display":false,"email":"[email protected]","identity":"nature","isNatureJournal":true,"hasQc":false,"allowDirectSubmit":false,"externalIdentity":"nature","sideBox":"Learn more about [Nature](http://www.nature.com/nature/)","snPcode":"","submissionUrl":"","title":"Nature","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"ejp","reportingPortfolio":"Nature","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"109b669f-e8d7-4c5e-8b18-6752c23a2600","owner":[],"postedDate":"February 12th, 2026","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"under-review","subjectAreas":[{"id":62750256,"name":"Physical sciences/Astronomy and planetary science/Astronomy and astrophysics/Stellar evolution"},{"id":62750257,"name":"Physical sciences/Astronomy and planetary science/Astronomy and astrophysics/Interstellar medium"}],"tags":[],"updatedAt":"2026-04-28T22:30:21+00:00","versionOfRecord":[],"versionCreatedAt":"2026-02-12 04:10:54","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-8693689","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-8693689","identity":"rs-8693689","version":["v1"]},"buildId":"XKTyCvWXoU3ODBz1xrDgd","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}