Users September 2026

users@lists.einsteintoolkit.org

7 participants
21 discussions

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

1 0

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

1 0

[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.

1 0

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

2 1

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!

1 0

[nr-community-call] Next NR community call: Monday, Sep 14
by Nils Vu 10 Sep '26

10 Sep '26

Dear Numerical Relativists, Hope you had a nice summer! Our first NR community call of the new season will be on Monday, Sep 14 (9am Pacific, noon Eastern, 6pm CET). Our speakers will be Jesse Buffaloe (UTK / Thornado) and Himanshu Chaudhary (Caltech / SXS). You can find the schedule in the wiki: https://github.com/sxs-collaboration/nr-community-call/wiki We have 3 remaining slots available for the rest of the year. Please sign up on the wiki if you’d like to speak at an NR community call this year! As always: - 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 Best, Nils — Nils Vu, Ph.D. (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.

1 0

Einstein Toolkit Meeting Reminder
by users＠einsteintoolkit.org 09 Sep '26

09 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

1 0

Re: [Users] New thorn proposal: Geodesic — test-particle geodesic tracking for the Einstein Toolkit
by Yuhua Li 09 Sep '26

09 Sep '26

Dear all, dear Steve, (Continuing the discussion on the list, as suggested.) Thank you, Steve, for the review of the thorn and the paper draft. The evaluation gave me a clear roadmap, and I have now completed the rework in two stages; everything is pushed to https://github.com/wylyhzh/Geodesic. First stage (mechanical fixes): - geodesics_integrate runs with OPTIONS: global and declares READS on the ADMBase metric; Geodesic_ParamCheck is actually scheduled; - the particle arrays are DISTRIB=CONSTANT and checkpointable; the unused CoordGauge inherit and the hard KerrSchild dependency are gone (the thorn has its own M, a parameters for the exact mode); - code fixes: the metric inversion no longer returns a garbage inverse on singular pivots; the interpolation domain guard matches the 6th-order stencil; Cactus logging was moved out of the OpenMP loop; omp.h is guarded by _OPENMP; - par/example.par now uses only public thorns and runs on a stock ET checkout; the README states the current limitations explicitly (unigrid, single refinement level, particle arrays replicated on every rank). Second stage (tests, documentation, robustness): - Testsuite: test/ now contains three tests, all passing under the Cactus testsuite harness: circ_orbit (full particle state compared against reference data), circ_orbit_conserved (a postproc checks that E and L_z stay constant), and circ_orbit_mpi (the same run on 2 MPI ranks, bit-identical to the single-rank result); - Documentation: doc/documentation.tex (ThornGuide format) is included; - particle loss handling is now a run-time policy (particle_loss_policy = drop / flag / respawn), with drop as the default; - the per-particle cache is allocated once and reused across steps, which removes the per-step allocation churn the review pointed out. The remaining architectural items (correct behaviour with more than one MPI rank, interpolation through CarpetInterp/AEILocalInterp, and the time derivative of the metric from the ADMBase timelevels) are a larger rewrite whose priority I would like to discuss with the maintainers. On the question of community interest and a published paper: the paper describing the method and the verification is included in the repository (doc/geodesic_paper.pdf). I plan to submit it to arXiv (gr-qc, cross-listed with astro-ph.HE) once it has benefited from the community's feedback, and subsequently to a journal, e.g. Classical and Quantum Gravity. I hope this addresses the "current interest" criterion in due course. With this, I believe the thorn now meets the contribution page's requirements on documentation, examples and self-tests, within its stated scope. I would appreciate guidance on the next step, and on whether the thorn could be considered for an "incoming" listing. Best regards, Yuhua Li At 2026-09-09 22:18:59, "Steven R. Brandt" <sbrandt(a)cct.lsu.edu> wrote: Sure, we can go ahead with email. However, you should probably be sending to users(a)einsteintoolkit.org to address the group. See: The current working procedure for contributions is: Author(s) contacts the Einstein Toolkit consortium (e.g. through the users or maintainers mail lists) about software that they intend to contribute Discussions take place between the maintainers and author(s) to discuss issues above. One question you need to address at some ponit: To focus development and support, optimize resources, and provide best practises, the Einstein Toolkit components should be of current interest to the community. This is phrased ambiguously, but usually means there's a paper published in a reputable journal somewhere. --Steve On 9/9/2026 8:37 AM, Yuhua Li wrote: Dear Steve, Thank you for taking the time to look at the thorn and the paper, and for forwarding the evaluation. I have gone through it carefully. I agree with the two problems you singled out — the missing READS/WRITES clauses and the MPI layout — and most of the other findings are also correct. The evaluation gave me a clear roadmap, and I have now completed the first, mechanical stage of the rework: - schedule.ccl: geodesics_integrate now runs with OPTIONS: global and declares READS on the ADMBase metric; Geodesic_ParamCheck is actually scheduled at CCTK_PARAMCHECK; - interface.ccl: the particle arrays are now DISTRIB=CONSTANT and checkpointable; the unused CoordGauge inherit is gone; - param.ccl: the hard KerrSchild dependency was removed — the thorn has its own M and a parameters for the exact mode; - storage now follows particle_n_total instead of particle_n; - code fixes: the 4x4 metric inversion no longer returns a garbage inverse on singular pivots; the interpolation domain guard now matches the 6th-order stencil; Cactus logging was moved out of the OpenMP loop; omp.h is guarded by _OPENMP; the parameter prose and the copyright headers are fixed; - par/example.par now uses only public thorns and runs on a stock ET checkout; the README states the current limitations explicitly (single refinement level, unigrid, particle arrays replicated on every rank). All of this is pushed to the repository, and the thorn rebuilds and runs cleanly. The remaining, architectural items — correct behaviour under MPI with more than one rank, interpolation through CarpetInterp/AEILocalInterp, and the time derivative of the metric from the ADMBase timelevels — are a larger rewrite. I would like to discuss their priority with the maintainers before starting, and I will state the current domain clearly in the paper as well: unigrid, a single MPI process, stationary or slowly evolving metrics. For the ET contribution requirements I still plan to add the doc/documentation.tex ThornGuide documentation and a test/ case (conservation of E and Lz on a circular Kerr orbit) — a pointer to a good example test to follow would be appreciated. About the weekly meetings: I would honestly prefer not to join, because my spoken English — especially listening — is not good enough for a live discussion, and I cannot change that in the short term. I hope we can communicate in writing instead, here on the mailing list or by email; if a short written summary for one of the meetings would help, I am happy to provide one. Thank you again for the constructive feedback. Best regards, Yuhua Li At 2026-09-09 07:07:21, "Steven R. Brandt" <sbrandt(a)cct.lsu.edu> wrote: Yuhua, I had Grok take a look at your thorn and paper. You will find the feedback attached (eval.md). At least some of the things it identifies are valid problems, namely the lack of READS/WRITES clauses in the schedule and MPI support. You may want to consider joining one of the weekly ET meetings to make your case (I realize that the time will probably be challenging for you). --Steve On 9/8/2026 11:00 AM, Yuhua Li wrote: Dear Steven, Thank you for the quick and encouraging reply, and for the pointer to the contribution process. To answer your question directly: my goal is to have Geodesic included in the Einstein Toolkit, and I am willing to follow the process described at https://einsteintoolkit.org/contribute.html step by step. In the meantime, I would be glad if the thorn could be added to the "Thorns we know of" list. Where the thorn stands with respect to the requirements: - Documentation: the repository has a README with purpose, build and usage instructions and a parameter table; the algorithms and the verification are described in the paper draft (doc/geodesic_paper.pdf). - Examples: par/example.par is a complete, runnable example, and the par/ directory contains the parameter files that reproduce every result reported in the paper. I am happy to add an automated test in the ET test-suite format — a pointer to a good example test to follow would be appreciated. - Licence: GPLv2+, included as COPYING. - Hosting: the code is on GitHub (https://github.com/wylyhzh/Geodesic). I am open to hosting it at einsteintoolkit.org if that is preferred. Please let me know what the next step should be — for example, whether the thorn can be placed into an "incoming" repository, and what the review will look at first. I will respond to any requested changes in a timely manner. Best regards, Yuhua Li At 2026-09-08 22:41:39, "Steven R. Brandt via Users" <users(a)einsteintoolkit.org> wrote: Dear Yuhua, Thank you for writing and for putting the code and the paper draft in a public repository under GPLv2+. Independent contributions of this kind are welcome, and a test-particle geodesic tracker is something we don't have: the ET currently ships fluid tracers (particle_tracerET) and puncture tracking (PunctureTracker), but not a timelike geodesic integrator on the 3+1 metric. Were you hoping to have it included in the ET, or were you just looking to share the code with the community? If so, we can help you with the process. Please take a look at https://einsteintoolkit.org/contribute.html if you haven't already. If you would like to do something less formal, we can share your link on our list of "thorns we know of": https://docs.einsteintoolkit.org/et-docs/Thorns_we_know_of Best regards, Steven R. Brandt On 9/8/2026 12:28 AM, Yuhua Li via Users wrote: Dear Einstein Toolkit community, I am a retired researcher (background in mathematics and computer science) working independently from China. Over the past ten years I have been building a test-particle geodesic tracker for the Einstein Toolkit, and I would like to share it with the community. The Geodesic thorn integrates geodesics for large numbers of test particles in Kerr–Schild Cartesian coordinates. It supports (i) the exact Kerr–Schild metric, independent of the grid (verified symbolically to be the vacuum solution to machine precision), and (ii) 27-point local Lagrange interpolation of the grid metric, so it also works for arbitrary spacetimes carried on the grid (e.g., GRHydro evolutions). The per-particle integration is fully independent and parallelized with OpenMP (validated with 10^4 particles). The code (GPLv2+), the configuration files used in the validation runs, and a paper draft describing the method and verification are all available in this public repository: https://github.com/wylyhzh/Geodesic I plan to submit the paper to arXiv (gr-qc, cross-list astro-ph.HE) once it has benefited from the community's feedback. I would appreciate: (1) feedback on whether the thorn meets ET standards, and what would be needed to have it listed with the ET thorns; (2) any comments on the paper. I am most comfortable discussing in writing, so I would prefer to continue the conversation here on the mailing list or by email, whichever is more convenient. I am happy to provide any further information. Best regards, Yuhua Li _______________________________________________ Users mailing list Users@einsteintoolkit.orghttp://lists.einsteintoolkit.org/mailman/listinfo/users

1 0

New thorn proposal: Geodesic — test-particle geodesic tracking for the Einstein Toolkit
by Yuhua Li 08 Sep '26

08 Sep '26

Dear Einstein Toolkit community, I am a retired researcher (background in mathematics and computer science) working independently from China. Over the past ten years I have been building a test-particle geodesic tracker for the Einstein Toolkit, and I would like to share it with the community. The Geodesic thorn integrates geodesics for large numbers of test particles in Kerr–Schild Cartesian coordinates. It supports (i) the exact Kerr–Schild metric, independent of the grid (verified symbolically to be the vacuum solution to machine precision), and (ii) 27-point local Lagrange interpolation of the grid metric, so it also works for arbitrary spacetimes carried on the grid (e.g., GRHydro evolutions). The per-particle integration is fully independent and parallelized with OpenMP (validated with 10^4 particles). The code (GPLv2+), the configuration files used in the validation runs, and a paper draft describing the method and verification are all available in this public repository: https://github.com/wylyhzh/Geodesic I plan to submit the paper to arXiv (gr-qc, cross-list astro-ph.HE) once it has benefited from the community's feedback. I would appreciate: (1) feedback on whether the thorn meets ET standards, and what would be needed to have it listed with the ET thorns; (2) any comments on the paper. I am most comfortable discussing in writing, so I would prefer to continue the conversation here on the mailing list or by email, whichever is more convenient. I am happy to provide any further information. Best regards, Yuhua Li

2 1

Agenda for Thursday's Meeting
by users＠einsteintoolkit.org 07 Sep '26

07 Sep '26

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

1 0

2026

2025

2024

2023

2022

2021

2020

2019

2018

2017

2016

2015

2014

2013

2012

2011

2010

Users September 2026