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Agenda for Thursday's Meeting
by users＠einsteintoolkit.org 21 Sep '26

21 Sep '26

Please update the Wiki with agenda items for Thursday's meeting. Thanks! https://docs.einsteintoolkit.org/et-docs/meeting_agenda --The Maintainers

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Fwd: Applications Open for Postdoctoral Research Positions at Perimeter Institute for Theoretical Physics
by Roland Haas 21 Sep '26

21 Sep '26

-------- Original Message -------- SUBJECT: Applications Open for Postdoctoral Research Positions DATE: 2026-09-21 10:05 FROM: William East <academic(a)perimeterinstitute.ca> TO: rhaas(a)mail.ubc.ca REPLY-TO: peopleandculture(a)perimeterinstitute.ca [CAUTION: Non-UBC Email] Perimeter Institute for Theoretical Physics is inviting applications for Postdoctoral Research positions. ͏ ͏ ͏ ͏ ͏ ͏ ͏ ͏ ͏ ͏ ͏ ͏ ͏ ͏ ͏ ͏ ͏ ͏ ͏ ͏ ͏ ͏ ͏ ͏ ͏ ͏ ͏ ͏ ͏ ͏ ͏ ͏ ͏ ͏ ͏ ͏ ͏ ͏ ͏ ͏ ͏ ͏ ͏ ͏ ͏ ͏ ͏ ͏ ͏ ͏ ͏ ͏ ͏ ͏ ͏ ͏ ͏ ͏ ͏ ͏ ͏ ͏ ͏ ͏ ͏ ͏ ͏ ͏ ͏ ͏ ͏ ͏ ͏ ͏ ͏ ͏ ͏ ͏ ͏ ͏ ͏ ͏ ͏ ͏ ͏ ͏ ͏ ͏ ͏ ͏ ͏ ͏ ͏ ͏ ͏ ͏ ͏ ͏ ͏ ͏ ͏ ͏ ͏ ͏ ͏ ͏ ͏ ͏ ͏ ͏ ͏ ͏ ͏ ͏ ͏ ͏ ͏ ͏ ͏ ͏ Dear Valued Colleague, Perimeter Institute for Theoretical Physics is inviting applications for the Postdoctoral Research Program [1]. For more information, please visit the job posting [2]. We hope you will share the news by: * Forwarding this information directly to prospective candidates who may be interested in this opportunity * Downloading, printing, and hanging the poster [3] * Sharing LinkedIn [4] and Facebook [5] posts with your social networks Perimeter Institute offers a dynamic, multi-disciplinary environment with maximum research freedom and opportunity to collaborate. We welcome all candidates to apply by November 6, 2026 but applications will be considered until all positions are filled. Thank you in advance for forwarding and sharing this information. Sincerely, William East Committee Chair Links: ------ [1] https://landing.perimeterinstitute.ca/e3t/Ctc/2I+113/cjL-604/VWy7sc2gdh7VW3… 3bYncS8TB7jMW2Gfc0n3xXmdJW6DmBg26P8JB6W1yv_6f3qkVnyW1qzrnm55SSmFW8-tkVb641HFGW8dygWn77VLqxV72Zq66cPmJyV8ZtLS29yzH6W4bql0y5DDBhTW5MTHRx4g4_6JW4RPZPd8Ny8sRW2KtWMm5NmTQtMpZHcRfr_rwW5qtqf44k0zNBW41HKz544ypzNW2gjKqg59rbJ9W5Jl52y5n94VjW8bhWdV8Zbkv5W4rCMCB4Kk-_dVPr-pc5CqZlXW3tfQkn51tb8zdSwHk204 [2] https://landing.perimeterinstitute.ca/e3t/Ctc/2I+113/cjL-604/VWy7sc2gdh7VW3… [3] https://landing.perimeterinstitute.ca/e3t/Ctc/2I+113/cjL-604/VWy7sc2gdh7VW3… [4] https://landing.perimeterinstitute.ca/e3t/Ctc/2I+113/cjL-604/VWy7sc2gdh7VW3… [5] https://landing.perimeterinstitute.ca/e3t/Ctc/2I+113/cjL-604/VWy7sc2gdh7VW3…

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Meeting minutes for 09/17/26
by Deborah Ferguson 17 Sep '26

17 Sep '26

Chair: Roland Minute taker: Deborah Attendees: Deborah, Roland, Jordan, Peter, Maxwell, Zach, Nikolai, Ameen, Yuhua, Lucas Accumulated updates after the release - AMRex merged in - Mchlachlan updates - peter has been able to compile, but having some run issues Status of issues on github - the new tickets based on github are now up - yet to update the website - some tickets ready to be added to it - tickets are now authored by a bitbucket-to-github transition bot - mentions resolve as a hash instead of a username - you may have an email inviting you to join the ETK organization - ping tickets if need be to adjust update times - thank you Zach for all his work - Jordan suggesting sending an email to the mailing list about this (will be done soon) Potentially hosting the wiki on github - reduce LSU reliance - previously considering doing this on bitbucket (old issue: https://github.com/EinsteinToolkit/tickets/issues/2256) - github wiki seems better so may be worth it - things to consider - we want tables - media wiki does have more capability, anything we need? Unanswered questions - New thorn proposal - will be discussed over email - Independent researcher wanting to use ETK to test a theory - possibly an AI? Issues: - GetComponents suggestion / pull request from Jordan - adds options to switch branch - Roland isn’t sure whether this will fully make it updatedable - would need to also adjust symbolic links - likely would get you 80% of the way there - Cottonmouth - is already included, not sure why the ticket is still open - Lucas will look into - FUKA ticket from Samuel Tootle - Peter will take a look - will see if Samuel can join a call at some point - Regression in TwoPuncturesX - Zach thinks this has been resolved - wait to discuss next week - BHNS gallery example - needs to be closed - BHaHAHA - needs to be closed - also close its duplicate - CapyrX has been postponed - CarpetRegrid2 bug - Jordan provided a reproducer with a minimal example - Jordan will ping it to bring it to the top AOB - Zach tells us to expect a few new thorns from his side for the next release - Baikal update coming soon to be much faster ----------------------------------------- Deborah Ferguson Assistant Professor The University of Rhode Island

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Geodesic: a test-particle geodesic thorn (AMR-verified) - for today's weekly users call
by Yuhua Li 16 Sep '26

16 Sep '26

Dear all, At today's weekly users call I would like to briefly present Geodesic, a new thorn that integrates test-particle geodesics in Kerr--Schild Cartesian coordinates, and ask for feedback before submitting it to the Einstein Toolkit. Features - Two metric modes: an exact analytic Kerr--Schild metric (grid-independent, symbolically verified to be a vacuum solution at machine precision), and a grid mode that samples the ADMBase fields with three interchangeable samplers selected by one parameter: local27 (default, 27-point local Lagrange fit), aei (fourth-order pointwise, via AEILocalInterp), and carpet (second-order pointwise quadratic Lagrange). - Adaptive RKF45 integration with per-step renormalization of the four-velocity; d_t g recovered from the three most recent ADMBase time levels (stationary metrics are auto-detected). - AMR-ready: each sampler reads the refinement level that contains the particle, so geodesics can be integrated inside a Carpet AMR evolution (with 4:1 subcycling) without any change to the integrator. - OpenMP-parallel particle loop: scales to 10^4 particles (9.2x speedup, 10.4% efficiency on 88 threads); embedded in a full GRHydro evolution, tracking 10^4 particles costs only ~3.1% of the wall time. Verification - E, L_z and the norm conserved to ~1e-9 over T = 1000 M on three distinct bound orbits (circular, tilted, eccentric). - Grid convergence of the default sampler with a measured local order of 3.7 (formal order three) against an independent reference. - Five-way comparison of the exact metric and the three samplers on a precessing orbit of 200 particles close to the plunge boundary. - New: on a 3-level Carpet AMR mesh (50^3 base, dx=1; refinement boxes of half-width 16/8, factor 2), all three samplers reproduce the unigrid reference orbit of conv100 over ~1.05 orbital periods (t = 0..150.1): radial deviations 0.4% (local27), 0.5% (aei), 2.3% (carpet, consistent with its second formal order), with no lost particles and no NaNs. Code and configurations - Repository (GPLv2+): https://github.com/wylyhzh/Geodesic - Includes a 7-test testsuite, ThornGuide documentation, and the parameter files used for the results above (including the three AMR-vs-unigrid comparison setups). - A paper describing the implementation and the verification suite is in preparation. Known limitation - The multi-process (MPI) particle layout is implemented (DISTRIB=CONSTANT, rank-0 integration with state synchronization) but has not yet been exercised with the current rework; single-process OpenMP runs are the tested configuration. The aei sampler in addition needs single-process runs or AEILocalInterp's N_boundary_points_omit when its fourth-order stencil would cross a processor boundary. Any feedback is very welcome - in particular on whether the thorn should be proposed as EinsteinAnalysis/Geodesic. Best regards, Yuhua Li

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Einstein Toolkit Meeting Reminder
by users＠einsteintoolkit.org 16 Sep '26

16 Sep '26

Hello, Please consider joining the weekly Einstein Toolkit phone call at 9:00 am US central time on Thursdays. For details on how to connect and what agenda items are to be discussed, use the link below. https://docs.einsteintoolkit.org/et-docs/Main_Page#Weekly_Users_Call --The Maintainers

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Independent research enquiry — numerical test of a proposed star-formation model
by Shaun Osgathorpe 15 Sep '26

15 Sep '26

Dear Einstein Toolkit Users and Maintainers, My name is Shaun Osgathorpe. I am an independent amateur researcher based in the UK, without a university affiliation or PhD, and I am contacting the Einstein Toolkit community because I would like to determine whether a physical hypothesis I have been developing can be tested properly using established numerical-relativity and GRMHD methods. I want to be clear from the beginning that I am not presenting the hypothesis as established physics. My objective is to test it rigorously and allow the numerical results to reject, modify or support individual parts of the model. I have been developing a proposed multi-stage scenario involving pre-existing matter, gravitational interactions, collisions, shocks, cooling, magnetic fields and eventual gravitational gathering and possible star formation. The current proposed sequence is broadly: Pre-existing matter and gas → gravitational/tidal interaction → collision or close interaction → compression, shocks, heating and mixing → cooling and radiation → sustained gathering/convergence where physically permitted → possible gravitationally bound structure → possible gravitational contraction → fragmentation or protostellar formation if the equations permit it → eventual stellar and planetary-system evolution. An important part of the model is that I do NOT assume that a collision creates a star. A collision would only change the physical environment. Gathering and gravitational collapse would also be treated as separate outcomes rather than assuming that one automatically follows the other. I have also been investigating a possible role for neutron-star merger ejecta. The proposed mechanism is not that a neutron-star merger creates an entire star or gas cloud by itself. Instead, neutron-rich ejecta and heavy-element enrichment would interact with pre-existing gas, while nearby gravitational interactions could alter and compress that material. Subsequent cooling, accretion and gravitational instability would then have to develop naturally. I would like to test whether this is physically viable rather than assume that it is. The numerical experiment I eventually want to perform would include, where appropriate: • 3D hydrodynamics/GRMHD • self-gravity • spatially varying density, pressure, temperature and velocity • collision velocity and impact parameter • angular momentum and rotation • tidal fields and tidal-tensor eigenvalues • magnetic-field strength, geometry and orientation • magnetic pressure and magnetic tension • radiative cooling and energy loss • appropriate equations of state • neutron-rich material/ejecta • pulsar or magnetised compact-object electromagnetic forcing • gravitational-wave tidal effects • adaptive mesh refinement • multiple numerical resolutions • convergence testing. I would particularly like to investigate whether magnetic fields and time-dependent electromagnetic fields can alter gathering, compression, turbulence, angular-momentum transport or fragmentation. For gravitational waves, I do not want to model them simply as an attractive or repulsive force. I understand that their local effect is an alternating tidal distortion. For a simple + polarised linearised wave, for example, the relative accelerations can be represented schematically as a_x = (1/2) h¨ x a_y = -(1/2) h¨ y. A production calculation should preferably generate the gravitational radiation self-consistently through numerical relativity rather than impose an arbitrary force. I have already performed reduced numerical experiments locally to test parts of the mathematics and to identify useful parameter ranges. These have included: • 3D self-gravitating particle calculations • corrected gravitational-wave tidal forcing • magnetic/pulsar forcing proxies • cooling • gathering diagnostics • bound-state diagnostics • Jeans diagnostics • resolution refinement • timestep refinement • parameter sweeps • conservation checks. The reduced calculations have produced interesting behaviour, but I do not regard them as astrophysical evidence. In particular, I have found that the apparent effect of gravitational waves can be very small and can change with parameters. This is exactly why I would like to move toward a proper production calculation rather than extrapolate from a simplified model. One reduced Stage 3–8 parameter sweep, for example, produced the following fractions of its deliberately sampled parameter space: Gathering diagnostic: 90.102% Bound diagnostic: 33.371% Jeans diagnostic: 14.625% Cooling-time/free-fall diagnostic: 87.606% All combined reduced criteria: 5.589% These numbers are NOT being presented as probabilities of star formation. They are simply outputs from a chosen synthetic parameter space. I would therefore like expert guidance on whether the proposed numerical experiment can be formulated correctly using the Einstein Toolkit. In particular, I would appreciate advice on: 1. Whether Einstein Toolkit is an appropriate framework for this problem. 2. Which existing Einstein Toolkit components would be most appropriate. 3. Whether GRHayL/IllinoisGRMHD and CarpetX/AMR would be suitable starting points. 4. How best to represent the gas, magnetic fields, compact-object interaction and radiation. 5. Whether the proposed gravitational-wave treatment is appropriate. 6. What aspects of the model should be removed because they are physically unjustified. 7. What initial conditions would be scientifically defensible. 8. What resolution would be required before conclusions could be trusted. 9. Whether a smaller test case could be run first before attempting a large HPC calculation. 10. Whether there is an appropriate tutorial, community project or researcher who could advise an independent new user. I would also like to use matched controls, for example: A. Gravity + tides B. Gravity + magnetic fields C. Gravity + cooling D. Gravity + magnetic fields + cooling E. Gravity + gravitational waves F. Gravity + gravitational waves + magnetic fields G. Gravity + gravitational waves + magnetic fields + pulsar electromagnetic forcing with corresponding no-GW, no-magnetic-field, no-cooling and no-rotation controls. The key scientific question is not "can I make the simulation form a star?" It is: "Under what initial conditions, if any, do the established equations produce sustained gathering, a gravitationally bound structure, contraction, fragmentation and eventual protostellar formation, and which physical mechanisms materially affect that outcome?" I would be very grateful for any advice from members of the Einstein Toolkit community, including advice that shows the hypothesis is incorrectly formulated. I am also willing to start with a much smaller and simpler problem if that is the scientifically appropriate route. I understand that I am an amateur and that a production numerical-relativity calculation requires considerably more expertise than I currently have. I am therefore approaching the community primarily for technical and scientific guidance rather than assuming that my proposed model is correct. If useful, I can provide the equations, parameter ranges, reduced numerical results, control matrix and numerical job specification that I have developed so far. Thank you for taking the time to read this, and for any guidance you may be able to provide. Kind regards, Shaun Osgathorpe Independent researcher United Kingdom

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Agenda for Thursday's Meeting
by users＠einsteintoolkit.org 14 Sep '26

14 Sep '26

Please update the Wiki with agenda items for Thursday's meeting. Thanks! https://docs.einsteintoolkit.org/et-docs/meeting_agenda --The Maintainers

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[nr-community-call] Today: NR community call at 9am Pacific / noon NYC / 5pm London / 6pm CET (NEW Zoom link!)
by Nils Vu 14 Sep '26

14 Sep '26

Dear Numerical Relativists, We’ll have our NR community call today, Monday Sep 14, 9am LA / noon NYC / 5pm London / 6pm CET in this Zoom room (please note NEW Zoom link!): https://uzh.zoom.us/j/69955182150?pwd=uv1tSnkUKdbHW5VcfTN8JEiaS943VX.1 Our speakers today will be Jesse Buffaloe (UTK / Thornado) and Himanshu Chaudhary (Caltech / SXS). - Feel free to circulate this information within the NR community. - Please subscribe to our mailing list <https://groups.google.com/u/1/a/black-holes.org/g/nr-community-call/> to receive info on the community calls in the future (or send a short message to nr-community-call+subscribe(a)black-holes.org <mailto:nr-community-call+subscribe@black-holes.org> to subscribe) and join our Slack <https://join.slack.com/t/generalrelativity/shared_invite/zt-dl4gqb6v-aAuw~p…> for discussions (channel: #nr-community-call <https://generalrelativity.slack.com/archives/C021LLTLK37>). - Please sign up for a slot <https://docs.google.com/forms/d/e/1FAIpQLSfoCnnCJve7J7Jzrpdlqw7nAbwWS_iuX_e…> in the schedule to speak at one of the community calls: https://github.com/sxs-collaboration/nr-community-call/wiki Looking forward to seeing you all later, Nils — Nils Vu (he/him) SNSF Ambizione Fellow University of Zurich To unsubscribe from this group and stop receiving emails from it, send an email to nr-community-call+unsubscribe(a)black-holes.org.

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New day & time for ETK meetings
by Ghadiri, Noora Rain 10 Sep '26

10 Sep '26

Dear all, I had sent this email to a wrong address before, apologies for the delay. Please take a moment to fill out your availability for 2026 Fall semester so we can decide on a time and day that works best for most meeting attendees. https://crab.fit/fall-26-etk-standing-meeting-235853 Best, Noora Ghadiri

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meeting minutes for 2026-09-10
by Steven R. Brandt 10 Sep '26

10 Sep '26

Present: Steve, Peter, Beyhan, Lucas, Roland, Maxwell, Deborah, Nikolai Date: 9/10/2026 Chair: Peter Minute Taker: Steve Issues in Github - Empty, Zach is not here. Got the last maintainer to agree to tickets. At the moment, it looks like the meeting time stays 9:00am on Thursday. We'll keep looking. Kyoto meeting - No updates. Short meetings are great!

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