First Detection of Hourglass-shaped Magnetic Fields in the L1544 Prestellar Core

First Detection of Hourglass-shaped Magnetic Fields in the L1544 Prestellar Core | 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 Article First Detection of Hourglass-shaped Magnetic Fields in the L1544 Prestellar Core Shinyoung Kim, Chang Won Lee, Kate Pattle, Derek Ward-Thompson, and 29 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-7429059/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 Stars form in dense, cold regions of interstellar clouds where gravity, turbulence, and magnetic fields interact. Magnetic fields are expected to regulate how gas contracts, but their role at the earliest, prestellar stage is poorly constrained, because polarized dust emission from the coldest cores is faint. Here we report submillimeter dust polarization observations of the well-studied prestellar core L1544, obtained with the James Clerk Maxwell Telescope SCUBA-2/POL-2 instrument as part of the BISTRO (B-fields in Star-forming Region Observations) survey. The data resolve a clearly pinched, hourglass-shaped magnetic field at the core center, representing the first detection in a prestellar core. The plane-of-sky field morphology matches classical predictions for magnetically regulated contraction and is consistent with previously reported slow infall and filament-fed accretion flows that deliver material into the core. From the polarization angle dispersion, we infer a magnetic field strength that implies an Alfvén speed above the measured infall speed and well below the free-fall velocity, indicating sub-Alfvénic, magnetically moderated contraction. These results show that the hourglass-shaped field geometry reported in some protostellar envelopes can already be present before a protostar forms, thereby bridging a key observational gap in the timeline of magnetically regulated star formation. As a nearby, representative core on the verge of star formation, L1544 now serves as a benchmark for testing theoretical models that couple gravity and magnetic fields in dense cores. Physical sciences/Astronomy and planetary science/Astronomy and astrophysics/Astrophysical magnetic fields Physical sciences/Astronomy and planetary science/Astronomy and astrophysics/Interstellar medium Physical sciences/Astronomy and planetary science/Astronomy and astrophysics/Stellar evolution 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. 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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-7429059","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Article","associatedPublications":[],"authors":[{"id":512020849,"identity":"06998dc4-58cc-4829-ae7d-e29eb242e9d1","order_by":0,"name":"Shinyoung 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Magnetic fields are expected to regulate how gas contracts, but their role at the earliest, prestellar stage is poorly constrained, because polarized dust emission from the coldest cores is faint. Here we report submillimeter dust polarization observations of the well-studied prestellar core L1544, obtained with the James Clerk Maxwell Telescope SCUBA-2/POL-2 instrument as part of the BISTRO (B-fields in Star-forming Region Observations) survey. The data resolve a clearly pinched, hourglass-shaped magnetic field at the core center, representing the first detection in a prestellar core. The plane-of-sky field morphology matches classical predictions for magnetically regulated contraction and is consistent with previously reported slow infall and filament-fed accretion flows that deliver material into the core. From the polarization angle dispersion, we infer a magnetic field strength that implies an Alfvén speed above the measured infall speed and well below the free-fall velocity, indicating sub-Alfvénic, magnetically moderated contraction. These results show that the hourglass-shaped field geometry reported in some protostellar envelopes can already be present before a protostar forms, thereby bridging a key observational gap in the timeline of magnetically regulated star formation. As a nearby, representative core on the verge of star formation, L1544 now serves as a benchmark for testing theoretical models that couple gravity and magnetic fields in dense cores.","manuscriptTitle":"First Detection of Hourglass-shaped Magnetic Fields in the L1544 Prestellar Core","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-10-24 11:47:33","doi":"10.21203/rs.3.rs-7429059/v1","editorialEvents":[],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"nature-astronomy","isNatureJournal":true,"hasQc":false,"allowDirectSubmit":false,"externalIdentity":"natastron","sideBox":"Learn more about [Nature Astronomy](http://www.nature.com/natastron/)","snPcode":"","submissionUrl":"","title":"Nature Astronomy","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"ejp","reportingPortfolio":"Nature Research","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"e65557a8-65f0-4081-89ea-09c6f70a285e","owner":[],"postedDate":"October 24th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"under-review","subjectAreas":[{"id":54382862,"name":"Physical sciences/Astronomy and planetary science/Astronomy and astrophysics/Astrophysical magnetic fields"},{"id":54382863,"name":"Physical sciences/Astronomy and planetary science/Astronomy and astrophysics/Interstellar medium"},{"id":54382864,"name":"Physical sciences/Astronomy and planetary science/Astronomy and astrophysics/Stellar evolution"}],"tags":[],"updatedAt":"2025-10-24T11:47:33+00:00","versionOfRecord":[],"versionCreatedAt":"2025-10-24 11:47:33","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-7429059","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-7429059","identity":"rs-7429059","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}