Archive for Turbulence

Weekly Update from the Open Journal of Astrophysics – 07/02/2026

Posted in OJAp Papers, Open Access, The Universe and Stuff with tags , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , on February 7, 2026 by telescoper

It’s Saturday once more so time for another update of activity at the Open Journal of Astrophysics. Since the last update we have published a further six papers, bringing the number in Volume 9 (2026) to 24 and the total so far published by OJAp up to 472.

I will continue to include the posts made on our Mastodon account (on Fediscience) to encourage you to visit it. Mastodon is a really excellent service, and a more than adequate replacement for X/Twitter which nobody should be using; these announcement also show the DOI for each paper.

The first paper to report this week is “The Impact of Star Formation and Feedback Recipes on the Stellar Mass and Interstellar Medium of High-Redshift Galaxies” by Harley Katz (U. Chicago, USA), Martin P. Rey (U. Oxford, UK), Corentin Cadiou (Lund U., Sweden) Taysun Kimm (Yonsei U., Korea) and Oscar Agertz (Lund). This paper was published on Monday 2nd February 2026 in the folder Astrophysics of Galaxies. It introduces MEGATRON, a new model for galaxy formation simulations, highlighting that feedback energy controls star formation at high redshift and highlighting the importance of the interstellar medium.

The overlay is here:

You can find the officially accepted version on arXiv here and the announcement on Fediverse here:

Open Journal of Astrophysics

New Publication at the Open Journal of Astrophysics: "The Impact of Star Formation and Feedback Recipes on the Stellar Mass and Interstellar Medium of High-Redshift Galaxies" by Harley Katz (U. Chicago, USA), Martin P. Rey (U. Oxford, UK), Corentin Cadiou (Lund U., Sweden) Taysun Kimm (Yonsei U., Korea) and Oscar Agertz (Lund)

doi.org/10.33232/001c.156097

February 2, 2026, 11:02 am 1 boosts 1 favorites

The second paper is “Photometric Redshifts in JWST Deep Fields: A Pixel-Based Alternative with DeepDISC” by Grant Merz (U. Illinois at Urbana-Champaign) and 6 others, all based in the USA. This paper was published on Monday February 2nd 2026 in the folder Instrumentation and Methods for Astrophysics. This paper explores the effectiveness of the DeepDISC machine learning algorithm in estimating photometric redshifts from near-infrared data, demonstrating its potential for larger image volumes and spectroscopic samples

The overlay for this one is here:

The official version of the paper can be found on arXiv here and the Fediverse announcement here:

Open Journal of Astrophysics

New Publication at the Open Journal of Astrophysics: "Photometric Redshifts in JWST Deep Fields: A Pixel-Based Alternative with DeepDISC" by Grant Merz (U. Illinois at Urbana-Champaign) and 6 others, all based in the USA

doi.org/10.33232/001c.156099

February 2, 2026, 11:23 am 1 boosts 0 favorites

Next, published on Wednesday 4th February in the folder Astrophysics of Galaxies, is “Inferring Interstellar Medium Density, Temperature, and Metallicity from Turbulent H II Regions” by Larrance Xing (U. Chicago, USA), Nicholas Choustikov (U. Oxford, UK), Harley Katz (U. Chicago) and Alex J. Cameron (DAWN, Denmark). This paper argues that supersonic turbulenc affects the interpretation of H II region properties, potentially impacting inferred metallicity, ionization, and excitation from in nebular emission lines, motivating more extensive modelling.

The overlay is here:

The official version can be found on arXiv here and the Fediverse announcement is here:

Open Journal of Astrophysics

New Publication at the Open Journal of Astrophysics: "Inferring Interstellar Medium Density, Temperature, and Metallicity from Turbulent H II Regions" by Larrance Xing (U. Chicago, USA), Nicholas Choustikov (U. Oxford, UK), Harley Katz (U. Chicago) and Alex J. Cameron (DAWN, Denmark)

doi.org/10.33232/001c.156223

February 4, 2026, 8:20 am 1 boosts 0 favorites

The fourth paper this week, also published on Wednesday 4th February, but in the folder Solar and Stellar Astrophysics, is “A Systematic Search for Big Dippers in ASAS-SN” by B. JoHantgen, D. M. Rowan, R. Forés-Toribio, C. S. Kochanek, & K. Z. Stanek (Ohio State University, USA), B. J. Shappee (U. Hawaii, USA), Subo Dong (Peking University), J. L. Prieto Universidad Diego Portales, Chile) and Todd A. Thompson (Ohio State). This study identifies 4 new dipper stars and 15 long-period eclipsing binary candidates using ASAS-SN light curves and multi-wavelength data, categorizing them based on their characteristics.

Here is the overlay:

The official version can be found on arXiv here and the Fediverse announcement is here:

Open Journal of Astrophysics

New Publication at the Open Journal of Astrophysics: "A Systematic Search for Big Dippers in ASAS-SN" by B. JoHantgen , D. M. Rowan, R. Forés-Toribio, C. S. Kochanek, & K. Z. Stanek (Ohio State University, USA), B. J. Shappee (U. Hawaii, USA), Subo Dong (Peking University), J. L. Prieto Universidad Diego Portales, Chile) and Todd A. Thompson (Ohio State)

doi.org/10.33232/001c.156224

February 4, 2026, 8:40 am 1 boosts 0 favorites

Fifth, and next to last this week we have “Unveiling the drivers of the Baryon Cycles with Interpretable Multi-step Machine Learning and Simulations” by Mst Shamima Khanom, Benjamin W. Keller and Javier Ignacio Saavedra Moreno (U. Memphis, USA). This paper was published on Thursday 5th February 2026 in the folder Astrophysics of Galaxies. This study uses machine learning methods to understand how galaxies lose or retain baryons, highlighting the relationship between baryon fraction and various galactic measurements.

The overlay is here:

The accepted version can be found on arXiv here, and the fediverse announcement is here:

Open Journal of Astrophysics

New Publication at the Open Journal of Astrophysics: "Unveiling the drivers of the Baryon Cycles with Interpretable Multi-step Machine Learning and Simulations" by Mst Shamima Khanom, Benjamin W. Keller and Javier Ignacio Saavedra Moreno (U. Memphis, USA)

doi.org/10.33232/001c.156271

February 5, 2026, 7:39 am 1 boosts 1 favorites

Finally for this week we have “The Bispectrum of Intrinsic Alignments: II. Precision Comparison Against Dark Matter Simulations” by Thomas Bakx (Utrecht U., Netherlands), Toshiki Kurita (MPA Garching, Germany), Alexander Eggemeier (U. Bonn, Germany), Nora Elisa Chisari (Utrecht) and Zvonimir Vlah (Ruđer Bošković Institute, Croatia). This paper was accepted in December, but publication got delayed by the Christmas effect so was published on February 6th 2026, in the folder Cosmology and Nongalactic Astrophysics. This study uses N-body simulations to accurately measure three-dimensional bispectra of halo intrinsic alignments and dark matter overdensities, providing a method to determine higher order shape bias parameters.

The overlay is here:

You can find the published version of the article here, and the Mastodon announcement is here:

Open Journal of Astrophysics

New Publication at the Open Journal of Astrophysics: "The Bispectrum of Intrinsic Alignments: II. Precision Comparison Against Dark Matter Simulations" by Thomas Bakx (Utrecht U., Netherlands), Toshiki Kurita (MPA Garching, Germany), Alexander Eggemeier (U. Bonn, Germany), Nora Elisa Chisari (Utrecht) and Zvonimir Vlah (Ruđer Bošković Institute, Croatia)

doi.org/10.33232/001c.156361

February 6, 2026, 7:43 am 1 boosts 0 favorites

And that concludes this week’s update. I will do another next Saturday.

Weekly Update from the Open Journal of Astrophysics – 22/11/2025

Posted in OJAp Papers, Open Access, The Universe and Stuff with tags , , , , , , , , , , , , , , , , , , , , , on November 22, 2025 by telescoper

It’s Saturday again, so it’s time for the usual update of the week’s new papers at the Open Journal of Astrophysics. Since the last update we have published another five papers, which brings the number in Volume 8 (2025) up to 180, and the total so far published by OJAp up to 415.

The first paper to report this week is “Probing Anisotropic Cosmic Birefringence with Foreground-Marginalised SPT B-mode Likelihoods” by Lennart Balkenhol (Sorbonne Université, France), A. Coerver (UC Berkeley, USA), C. L. Reichardt (U. Melbourne, Australia) and J. A. Zebrowski (U. Chicago, USA). This paper was published on Monday November 17th in the folder Cosmology and Nongalactic Astrophysics. It presents a way of using data from the Souh Pole Telescope (SPT) in the CMB-lite framework to constrain the level of cosmic birefringence.  The overlay is here:

You can find the officially accepted version on arXiv here and the The Fediverse announcement is here:

Open Journal of Astrophysics

New Publication at the Open Journal of Astrophysics: "Probing Anisotropic Cosmic Birefringence with Foreground-Marginalised SPT B-mode Likelihoods" by Lennart Balkenhol (Sorbonne Université, France), A. Coerver (UC Berkeley, USA), C. L. Reichardt (U. Melbourne, Australia) and J. A. Zebrowski (U. Chicago, USA)

doi.org/10.33232/001c.147459

November 17, 2025, 8:43 am 1 boosts 0 favorites

The second paper of the week is “Radio Observations of a Candidate Redback Millisecond Pulsar: 1FGL J0523.5-2529” by Owen. A. Johnson & E. F. Keane (Trinity College Dublin, Ireland), D. J. McKenna (ASTRON, NL), H. Qiu (SKAO, UK), S. J. Swihart (Insitute for Defense Analyses, USA), J. Strader (Michigan State U., USA) and M. McLaughlin (West Virginia U., USA). This one was published on Tuesday November 18th 2025 in the folder marked High-Energy Astrophysical Phenomena and it describes a search for radio emission from a candidate “redback pulsar” J0523.5-2529 resulting in upper limits but no detection.

The overlay is here:

You can find the official version of this one on arXiv here. The federated announcement on Mastodon is here:

Open Journal of Astrophysics

New Publication at the Open Journal of Astrophysics: "Radio Observations of a Candidate Redback Millisecond Pulsar: 1FGL J0523.5-2529" by Owen. A. Johnson & E. F. Keane (Trinity College Dublin, Ireland), D. J. McKenna (ASTRON, NL), H. Qiu (SKAO, UK), S. J. Swihart (Insitute for Defense Analyses, USA), J. Strader (Michigan State U., USA) and M. McLaughlin (West Virginia U., USA)

doi.org/10.33232/001c.147516

November 18, 2025, 8:42 am 1 boosts 0 favorites

Next one up is “The role of turbulence in setting the phase of the ISM and implications for the star formation rate” by Tine Colman (Université Paris-Saclay, France) and 13 others based in France, Germany, Italy and the UK. This was published in the folder Astrophysics of Galaxies on Tuesday November 18th. It descrtibes using a suite of stratified box simulations to explore the link between star formation, turbulence and the thermal state of the multi-phase interstellar medium (ISM).

The overlay is here:

You can find the official accepted version on arXiv here. The fediverse announcement is here:

Open Journal of Astrophysics

New Publication at the Open Journal of Astrophysics: "The role of turbulence in setting the phase of the ISM and implications for the star formation rate" by Tine Colman (Université Paris-Saclay, France) and 13 others based in France, Germany, Italy and the UK.

doi.org/10.33232/001c.147517

November 19, 2025, 8:19 am 0 boosts 0 favorites

The fourth paper of the week is “A Bimodal Metallicity Distribution Function in the Ultra-Faint Dwarf Galaxy Reticulum II” by Alice M. Luna (U. Chicago, USA) and 8 others based in the USA, Korea and Canada. This was published on Wednesday November 19th in the folder Astrophysics of Galaxies. It decribes low-resolution Magellan/IMACS spectroscopy of 167 stars in the ultra-faint galaxy Reticulum II, revealing a clearly bimodal distribution.

The overlay is here:

You can find the official published version on arXiv here. The Fediverse announcement follows:

Open Journal of Astrophysics

New Publication at the Open Journal of Astrophysics: "A Bimodal Metallicity Distribution Function in the Ultra-Faint Dwarf Galaxy Reticulum II" by Alice M. Luna (U. Chicago, USA) and 8 others based in the USA, Korea and Canada.

doi.org/10.33232/001c.147696

November 19, 2025, 8:37 am 0 boosts 0 favorites

The fifth and final paper for this week is “Cool Gas in the Circumgalactic Medium of Massive Post Starburst Galaxies” by Zoe Harvey, Sahyadri Krishna, Vivienne Wild & Rita Tojeiro (U. St Andrews, UK) and Paul Hewett (U. Cambridge, UK). This was published on Thursday November 20th in the folder Astrophysics of Galaxies.

The overlay is here:

The officially accepted version can be found on arXiv here. The Fediverse announcement is here:

Open Journal of Astrophysics

New Publication at the Open Journal of Astrophysics: "Cool Gas in the Circumgalactic Medium of Massive Post Starburst Galaxies" by Zoe Harvey, Sahyadri Krishna, Vivienne Wild & Rita Tojeiro (U. St Andrews, UK) and Paul Hewett (U. Cambridge, UK)

doi.org/10.33232/001c.147836

November 20, 2025, 9:02 am 1 boosts 0 favorites

And that concludes the update for this week. I will do another next Saturday.

Dond’escono quei vortici?

Posted in Education, Opera, The Universe and Stuff with tags , , , , on November 10, 2012 by telescoper

Just time for a quickie today. I seem to be writing that virtualy every day at this time, in fact. Anyway, yesterday I gave the last of a series of lectures on Fluid Dynamics during which I talked a little bit about the Navier-Stokes equation, and introduced the concept of turbulence, topic that Richard Feynman described as “the most important unsolved problem in classical physics”. Given that the origin of turbulence is so poorly understood, I had to cover it all fairly qualitatively but did at least explain that its onset is associated with high values of the Reynold’s Number, an interesting dimensionless number that characterizes the properties of viscous fluid flow in such a way as to bring out the dynamical similarity inherent in the equations. The difficulty is that there is no exact theory that allows one to calculate the critical value of the Reynold’s number and in any particular situation; that has to be determined by experiments, such as this one which shows turbulent vortices (or “eddies”) forming downstream of a cylindrical obstacle placed in flowing fluid. The (laminar) flow upstream, and in regions far from the cylinder, has no vorticity.

What happens is obviously extremely complicated because it involves a huge range of physical scales – the vorticity is generated by very small-scale interactions between the fluid elements and the boundary of the object past which they flow. It’s a very frustrating thing for a physicist, actually, because one’s gut feeling is that it should be possible to figure it out. After all, it’s “just” classical physics. It’s also of great practical importance in a huge range of fields. Nevertheless, despite all the progress in “exotic” field such as particle physics and cosmology, it remains an open question in many respects.

That’s why it’s important to teach undergraduates about it. Physics isn’t just about solved problems. It’s a living subject, and it’s important for students to know those fields where we don’t really know that much about what is going on…

PS. The title is a quotation from the libretto of Mozart’s opera, Don Giovanni, uttered by the eponymous Count as he is dragged down to hell. It translates as “Whence come these vortices?” Pretentious, moi?