Euclid, Gravitational Lensing, and Dark Matter

Posted in Euclid, The Universe and Stuff with tags , , on June 11, 2026 by telescoper

I’ve been slow onto a result which was announced last week concerning the detection weak gravitational lensing in the cluster Abell 2390 by the Euclid spacecraft and its use to determine the distribution of dark matter in the cluster. You can find a full discussion of the result here and the scientific paper is here.

The analysis was based on Early Release Observations of the cluster, a pretty picture of which are shown here:

Credit: ESA/Euclid/Euclid Consortium/NASA, image processing by J.-C. Cuillandre (CEA Paris-Saclay), G. Anselmi.

(The little blue patches are artefacts caused by internal reflections in the VIS instrument and can be dealt with in software.)

According to general relativity, the presence of any mass bends the path of light passing near it, producing gravitational lensing. The most famous examples of this are the giant arcs and multiple images associated with strong gravitational lensing, but these are very rare as they require good alignment between observer, lens and source.. Most lines of sight in the universe do not satisfy this condition so are in the weak lensing regime. Even in such cases, however, the presence of the foreground mass can be detected, by way of a systematic alignment in the orientation of background sources around the lensing mass. A circular background image would be distorted into an ellipse by this process. Unfortunately galaxies aren’t circular but are approximately elliptical, so the shape of each source is changed from an ellipse to differently shaped ellipse. The distortion is therefore impossible to detect in a single background source because we don’t know the intrinsic orientation of the galaxy, but the distortion of different sources is correlated in a particular way. Weak gravitational lensing is thus an intrinsically statistical measurement, but it provides a way to measure the masses of astronomical objects without requiring assumptions about their composition or dynamical state. Weak gravitational lensing observations are, however technically difficult to carry out and analyse, as one has to be very careful that no correlations are introduced by systematic errors in the optics.

Anyway, they say that a picture paints a thousand words so here are two pictures. On the left we see the shear axes as extracted from the above image and on the right the inferred dark matter distribution. You can slide the bar backwards and forwards to see how the two images relate.

Shear map (left) and inferred dark matter distribution (right)

You can see that the shear tends to be aligned tangentially to a line connecting the source the cluster centre, which is what theory would predict.

There’ll be much more of this sort of analysis in the full Euclid Survey. I hope to be able to give an update about this reasonably soon.

Scéalta Grá na hÉireann – The Ladies of Llangollen

Posted in History, Irish Language, LGBTQ+, Poetry with tags , , , , , , on June 10, 2026 by telescoper

I just watched a nice documentary programme on the Irish language channel TG4 in the series Scéalta Grá na h’Éireann (Ireland’s Greatest Loves). This one was about Lady Eleanor Charlotte Butler and the Honourable Sarah Ponsonby, often called The Ladies of Llangollen. The programme is available on the TG4 Player, actually, and it is possible I think to watch the whole thing anywhere in the world for free here. There’s also a little trailer on Youtube:

There’s an entire wikipedia page devoted to the Ladies of Llangollen, so there’s no need to reproduce it all here. However, for the sake of you who haven’t heard of them, they were. They were of Anglo-Irish extraction, both born in Ireland, and had been brought up just a few miles away from each other. They met in 1768 and immediately hit it off. They ran off together to avoid being forced into unwanted marriages, and moved to Wales in order to set up home  at Plas Newydd, near Llangollen in Denbighshire, in 1780.

They lived together for the best part of 50 years in Plas Newydd, in relative seclusion, devoting their time to private studies of literature and languages and improving their estate, comprehensively redesigning the house in a Gothic style, and adding a superb garden. They did not actively socialise and town-dwellers of Llangollen seem to have regarded them as eccentrics, simply referring to them as “The Ladies”.

Gradually, their life attracted the interest of the outside world. Their house became a haven for all manner of visitors, mostly writers such as Wordsworth, Robert Southey, Shelley, Byron and Scott, but also the military leader Duke of Wellington and industrialist Josiah Wedgwood; aristocratic novelist Caroline Lamb, who was born a Ponsonby, came to visit too. Even travellers from continental Europe had heard of the couple and came to visit them, for instance Prince Hermann von Pückler-Muskau, the German nobleman and landscape designer who wrote admiringly about them.

The story of the “romantic friendship” between these two ladies is both charming and moving, but it’s also fascinating to learn how their lifestyle was accepted and even celebrated by wider society. One might have thought their relationship would have been regarded as scandalous by their contemporaries, rather than being widely admired as it turned out to be. One is tempted to assume that their  “marriage” had a sexual dimension, which it may well have done, but it could have been a platonic, yet still romantic, friendship. As far as I’m concerned, that doesn’t really matter;  what I find inspiring about them is that they dared to be different.

Anyway, here is the beautiful sonnet that William Wordsworth wrote after meeting the Ladies of Llangollen in 1824, although I believe the Ladies took exception to the description of their magnificent house as a “low-roofed cot”!

 A stream, to mingle with your favourite Dee,
Along the vale of meditation flows;
So styled by those fierce Britons, pleased to see
In Nature's face the expression of repose;
Or haply there some pious hermit chose
To live and die, the peace of heaven his aim;
To whom the wild sequestered region owes
At this late day, its sanctifying name.
Glyn Cafaillgaroch, in the Cambrian tongue,
In ours, the Vale of Friendship, let 'this' spot
Be named; where, faithful to a low-roofed Cot,
On Deva's banks, ye have abode so long;
Sisters in love, a love allowed to climb,
Even on this earth, above the reach of Time!

Boards of Examinations

Posted in Education, Maynooth with tags , , , , , on June 10, 2026 by telescoper

Over the last few days we have been having our annual meetings of the Board of Examiners in the Department of Physics at Maynooth. This process began last Friday with a preliminary meeting of those involved in the theoretical side of the Department, continued on Monday with another preliminary meeting for the experimentalists, continued yesterday with a final meeting with both sides of the house and a visit by two External Examiners, and ended this morning with a meeting I couldn’t attend with feedback. This is the first time since the Departments of Theoretical Physics and Experimental Physics merged that we have run the process like this. I think one of the primary purposes of the merger was to streamline the bureaucracy, but it seems to have had the opposite effect, with everything taking much longer. It was ever thus.

Still, at least I got a nice dinner with the Externals.

Since we have reached the end of the academic year, we looked yesterday at the final grades of those students who are completing their studies this year in order to consider the classification of their degrees. Another (pleasant) duty of our Examination Board was to award prizes for the best performance, not just for finalists but for students at every stage, including the first year. These will be announced in due course.

But that’s not quite the end of it – there is an overall University Examination Board that covers all courses in the University to formally bring an end to the examination process. It is not until after all the Boards have done their business that the students get their marks. If all goes to plan, students will receive their final marks onThursday 25th June, a couple of weeks from now.

In previous years this would have been followed by a Consultation Day on which:

Staff will be available in all Departments to discuss results with students. Students are entitled to see their examination scripts if they wish, these will be generally available on this day or at another mutually convenient time.

In its drive to scrap everything that could possibly be useful to students, however, Maynooth University has now ditched the formal Consultation Day. Well, you can’t expect a University running an €11M surplus to put any resources into processes for advising students can you?

If I had my way we would actually give all students their marked examination scripts back as a matter of routine. Obviously examination scripts have to go through a pretty strict quality assurance process involving the whole paraphernalia of examination boards (including External Examiners), so the scripts can’t be given back immediately but once that process is complete there doesn’t seem to me any reason why we shouldn’t give their work, together with any feedback written on it,  back to the students in its entirety. I have heard it argued that under the provisions of the Data Protection Act students have a legal right to see what’s written on the scripts – as that constitutes part of their student record – but I’m not making a legalistic point here. My point is purely educational, based on the benefit to the student’s learning experience, so this is unlikely to be adopted.

So that’s my internal examination duties here at Maynooth done and dusted. In a month or so I have to travel abroad to be an external examiner at another institution.

Diamond Leads the Way on Open Access!

Posted in Open Access with tags , , on June 9, 2026 by telescoper

Here’s an interesting bit of information that might surprise sceptics of Diamond Open Access publishing (as demonstrated by the Open Journal of Astrophysics). I found it Mastodon:

The results were obtained using the excellent OpenAlex catalog(ue). It shows that of the over 25 million articles published as Open Access in the years 2020-2025 (inclusive), over 8.6 million (around 35%) were Diamond Open Access publications, i.e. free to authors and readers alike (without APC). Far from being the fringe model that many people think, these figures demonstrate that Diamond Open Access is the most frequently used form of OA. I predict that its use will increase with time.

The 2026 Leaving Certificate Mathematics Papers

Posted in Education, mathematics with tags , , on June 8, 2026 by telescoper

As I mentioned a few days ago, examinations for the 2026 school Leaving Certificate are under way. One of the interesting things about the Irish system is that the examination papers are put up online immediately after the examinations. Students took their first paper in Mathematics (either Ordinary or Higher level) on Friday and the second was this morning. There has been some reaction in the news here and here.

Anyway, I thought I’d share the Mathematics papers here so you can see what you think of them.

Here are the two Higher Mathematics papers:

The Ordinary Level papers are here:

They look reasonable to me. The thing that strikes me about them is that they are much more structured than the A-level mathematics examinations I took way back in 1981.

Comments are welcome through the box below.

Nine Purple Dots

Posted in Uncategorized with tags , , , on June 8, 2026 by telescoper

I posted this little optical illusion yesterday on BlueSky and it proved so popular I thought I’d repeat it here.Whichever of the purple dots you look directly at turns more purple:

I find the effect is stronger on a smaller screen (e.g. on a phone).

In a nutshell, this happens because your eyes have reduced sensitivity to blue light at the centre of your field of view so the purple (which is a mixture of red and blue) changes hue if you look directly at it. For more details see here and the following blog post:

I’m interested to know whether or not this works for people who are colour blind, so if that is you please let me know!

June – Francis Ledwidge

Posted in Poetry with tags , , , on June 7, 2026 by telescoper
Wilted Roses
Broom out the floor now, lay the fender by,
And plant this bee-sucked bough of woodbine there,
And let the window down. The butterfly
Floats in upon the sunbeam, and the fair
Tanned face of June, the nomad gipsy, laughts
Above her widespread wares,the while she tells
The farmer’s fortunes in the fields, and quaffs
The water from the spider-peopled wells.

The hedges are all drowned in green grass seas,
And bobbing poppies flare like Elmo’s light
While siren-like the pollen-stained bees
Drone in the clover depths. And up the height
The cuckoo’s voice is hoarse and broke with joy.
And on the lowland crops the crows make raid,
Nor fear the clappers of the farmer’s boy,
Who sleeps, like drunken Noah, in the shade.

And loop this red rose in that hazel ring
That snares your little ear, for June is short
And we must joy in it and dance and sing,
And from her bounty draw her rosy worth.
Ay! soon the swallows will be flying south,
The wind wheel north to gather in the snow
Even the roses spilt on youth’s red mouth
Will soon blow down the road all roses go.

by Francis Ledwidge (1887-1917)

Ledwidge was born in Slane, County Meath, in Ireland. He served in the British Army in the First World War and was killed at Passchendaele during the Third Battle of Ypres, just a few weeks before his 30th birthday. I’ve posted this poem before but was reminded of it when I saw some roses in my garden had died while I was away last week.

Weekly Update from the Open Journal of Astrophysics – 06/06/2026

Posted in OJAp Papers, Open Access, The Universe and Stuff with tags , , , , , , , , , , , , , , , , , , , , , , on June 6, 2026 by telescoper

Another Saturday, another update of activity at the Open Journal of Astrophysics. Since the last update we have published a further five papers, bringing the number in Volume 9 (2026) to 119 and the total so far published by OJAp up to 567.

I will continue to include the posts made on our Mastodon account (on Fediscience); these announcements also show the DOI for each paper.

The first paper to report this week, published on Tuesday 2nd June, is “The impact of the formation channel on gravitational-wave-galaxy cross-correlations” by Kabir Chakravarti (Chennai Mathematical Institute, India) and Federico R Urban (CEICO-FZU, Czech Republic). This article, published in the folder Cosmology and Nongalactic Astrophysics, explores how uncertainties in binary formation affect the cross-correlation signal between gravitational wave events and galaxy catalogues, finding that time-delay distribution significantly impacts the signal.

The overlay for this paper 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 the formation channel on gravitational-wave-galaxy cross-correlations" by Kabir Chakravarti (Chennai Mathematical Institute, India) and Federico R Urban (CEICO-FZU, Czech Republic)

doi.org/10.33232/001c.162783

June 2, 2026, 7:22 am 1 boosts 2 favorites

The second paper for this week, also published on Tuesday 2nd June but in the folder High-Energy Astrophysical Phenomena, is “Transient X-ray Sources as Extremely Eccentric Mass-Transfer Binaries with Compact Companions” by Jonathan I Katz and Michael A Nowak (Washington University, St Louis, USA). This article suggests that X-ray transients, similar to tidal disruption events, are produced in eccentric stellar-compact object binaries, with their frequency gradually increasing over time.

The overlay for this one looks like this:

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: "Transient X-ray Sources as Extremely Eccentric Mass-Transfer Binaries with Compact Companions" by Jonathan I Katz and Michael A Nowak (Washington University, USA)

doi.org/10.33232/001c.162784

June 2, 2026, 7:44 am 1 boosts 1 favorites

Next one up, the third paper of the week, also published on Tuesday 2nd June in the folder High-Energy Astrophysical Phenomena is “Resolving the (Debate About) Nozzle Shocks in Tidal Disruption Events” by Zachary L. Andalman & Eliot Quataert (Princeton U., USA), Eric R. Coughlin (Syracuse U. USA) and C. J. Nixon (U. Leeds, UK). This paper presents a model to understand the role of nozzle shocks in the circularization of stellar debris during a tidal disruption event when a star approaches a supermassive black hole (SMBH)

The overlay for this one is here:

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

Open Journal of Astrophysics

New Publication at the Open Journal of Astrophysics: "Resolving the (Debate About) Nozzle Shocks in Tidal Disruption Events" by Zachary L. Andalman & Eliot Quataert (Princeton U., USA), Eric R. Coughlin (Syracuse U. USA) and C. J. Nixon (U. Leeds, UK)

doi.org/10.33232/001c.162785

June 2, 2026, 7:52 am 1 boosts 1 favorites

The fourth paper this week, published on Wednesday 3rd June in the folder Cosmology and Nongalactic Astrophysics, is “Validating Digital Twins of the Local Universe with the Thermal Sunyaev-Zel’dovich Signal” by Richard Stiskalek (University of Oxford, UK) and Harry Desmond (University of Portsmouth, UK). The thermal Sunyaev-Zel’dovich effect and constrained simulations are used to analyze the thermal pressure of ionized gas in galaxy clusters and produce a set of digital twins for cosmological study.

The overlay is here:

The officially accepted version can be found on arXiv here and here is the Mastodon announcement:

Open Journal of Astrophysics

New Publication at the Open Journal of Astrophysics: "Validating Digital Twins of the Local Universe with the Thermal Sunyaev-Zel’dovich Signal" by Richard Stiskalek (U. Oxford, UK) and Harry Desmond (U. Portsmouth, UK)

doi.org/10.33232/001c.162811

June 3, 2026, 5:15 am 1 boosts 1 favorites

The fifth and final paper this week, published on Thursday 4th June in the folder Cosmology and Nongalactic Astrophysics is “Photon (Non)Conservation in the Reduced Speed of Light Approximation and How to (Almost) Fix It” by Nickolay Y. Gnedin (University of Chicago, USA). The “Reduced Speed of Light” approximation in cosmological simulations can lead to photon non-conservation, and while some missing photons can be counted, adding them back is challenging.

The overlay for this one is here:

The officially accepted version of this paper can be found on arXiv here and Mastodon announcement here

Open Journal of Astrophysics

New Publication at the Open Journal of Astrophysics: "Photon (Non)Conservation in the Reduced Speed of Light Approximation and How to (Almost) Fix It" by Nickolay Y. Gnedin (U. Chicago, USA)

doi.org/10.33232/001c.162879

June 4, 2026, 11:20 am 2 boosts 1 favorites

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

What Leads to Administrative Bloat?

Posted in Finance with tags , , , , , on June 5, 2026 by telescoper

I’ve commented many times before on this blog about runaway expenditure on management resulting in the diversion of resources away from the core missions of a university, i.e. teaching and research, while producing no significant improvement in the efficiency, and indeed often a deterioration, of administrative processes. David Graeber wrote a book called Bullshit Jobs about this phenomenon. Management response to this is generally to assert that this administrative bloat is a response to regulatory burden. Many of us working in higher education would instead argue that the entire sector has been hijacked by self-serving parasites who are deliberately sucking the lifeblood out of the system.

I just came across a paper on the Physics and Society section of arXiv that tries to explain management bloat from the point of view of systems theory. The title is What Leads to Administrative Bloat? A Dynamic Model of Administrative Cost and Waste, the authors are Vicky Chuqiao Yang and Levi Grenier of MIT and the abstract is here:

The functioning of complex systems depends on the coordination of diverse components, often supported by regulatory structures that incur costs. In human organizations, such costs manifest as administrative burden, which has been rising despite often reducing efficiency. Classic explanations point to bureaucrat self-interest or regulation, yet they do not explain variation across organizations or clarify how this burden can be reduced. Here, we develop a dynamical model of administrative growth that integrates known behavioral mechanisms of process creation, obsolescence, and removal. The model conceptualizes processes as developed for problem solving, but becoming obsolete as conditions change, while continuing to consume resources until actively pruned. This interplay generates two long-term outcomes: stable equilibrium or run-away growth. The threshold separating these outcomes is shaped by organizations’ propensity to create new processes when faced with problems, and their propensity to prune obsolete ones in response to administrative burden. Importantly, their effects are asymmetric: sufficiently high creation propensity leads to bloat regardless of pruning propensity. Faster environmental change shifts this threshold, making bloat more likely. Simulations of interventions show that lasting reductions in administrative costs and waste require permanent shifts in priorities and investments in distinguishing obsolete from useful processes. Temporary efforts or indiscriminate cuts provide only short-lived relief, and counterintuitively, prioritizing direct production can increase waste. Our work highlights a general mechanism by which well-intentioned problem-solving can create self-reinforcing inefficiencies in complex systems, offering insights possibly generalizable to broader applications, such as legal, policy, and software systems where obsolete elements accumulate.

Here’s a a figure from the paper that provides ample illustration of the problem:

You will find a similar phenomenon on display at universities across the world. In my view this is a large part of the crisis engulfing higher education in the United Kingdom.

It’s an interesting paper, based on a very simple model. The authors also suggest various ways in which this burden could be reduced. The problem with that is that there is no incentive at all for The Management (who hold all the power) to improve the situation, as that would involve eliminating the bullshit jobs held by many of their cronies. With university governance structures notoriously weak and compliant, who manages the Managers? The most likely response from my University would be to appoint a new Vice-President for Self-reinforcing Inefficiency…

INO Norma at the National Opera House

Posted in Opera with tags , , , , , , , , on June 4, 2026 by telescoper

I had seen the by Vincenzo Bellini‘s opera Norma twice (before yesterday evening) but both times were before I starting blogging so I was very pleased to see that Irish National Opera were doing a new production this year. It had a run at the Gaiety Theatre in Dublin, but I took the chance to see it National Opera House in Wexford. The first time I went there was last year and was to see a very different opera, although that one and Norma are both generally categorized by the term bel canto. I was so excited by the prospect of seeing this production that I made myself a Bellini on Saturday, only to discover that the cocktail is named after a different Bellini…

Norma is not performed all that often, largely because it is difficult to find a singer capable of doing justice to the title role which is acknowledged as being one of the most vocally demanding roles in all opera. It is a role that the great Maria Callas made her own in the 1950s which places the additional burden on the the singer of stepping out of the shadow of such a legend. I was delighted that in Salome Jicia INO found an artist who could meet the challenges of the part. She was stunning.

I think the part of Norma is difficult not only because of the vocal range of the part, from the lyrical beauty of the famous aria Casta Diva to the agility needed to perform the coloratura passages, but also for the sheer stamina required. There really is a lot of singing for her to do in this opera! Jicia took it in her stride. Bellini rarely gets the orchestra to double the vocal line, so the voice of the singer is very exposed. At times it’s like watching acrobatics knowing that there’s no safety net!

Anyway, to the plot.

Norma is a tragedia lirica in two Acts, set in ancient Gaul which is under occupation by the Romans. The eponymous Norma is the high priestess of the native Druids. She is also a complex chartacter, not least because she is in a relationship with a high-ranking Roman, Pollione, with whom she has had two kids. It turns out that Pollione is tiring of Norma and has turned his attention to her friend Adalgisa, who does not know about Pollione’s involvement with Norma.

The Opera begins with the heavily armed Gauls, led by Norma’s father Oroveso, planning to rise up against the Roman occupiers. But only Norma can sanction an armed rebellion and she says no. The aria Casta Diva expresses Norma’s desire for peace, but this is not just because she feels the Romans have greater military strength and would crush the rising, but because of her thing with Pollione. Over the course of the Opera we find out about Pollione’s infatuation with Adalgisa and their planned elopement to Rome which sends Norma into such a rage she threatens to kill her own children. Eventually Norma decides to change her mind about the uprising and calls for it to go ahead. Protocol requires a human sacrifice to initiate such a move, so the question is who is for the chop? Will it be Pollione, or Adalgisa? Norma surprises the assembled Gauls by confessing her sacreligious relationship with Pollione and declaring herself to be the sacrifice. Pollione is overcome by remorse at what he has done, and decides to join Norma in death.

Well, what did you expect in an Opera, a happy ending?

This production eschews the Normal (geddit?) setting of forest groves and scared shrines and places it in a sort of modern post-apocalyptic dystopia. The stage is dominated by barricades apparently hastily constructed from broken furniture and scrap metal. Lighting is sombre and claustrophobic. This jars with Bellini’s music when it evokes pastoral beauty – the music is too light and pretty for such a gloomy setting.

Gone are the swords, spears and druidic robes and in come AK-47s, pistols and somewhat scruffy modern-looking outfits. Even Norma’s dress is nothing fancy. The Gauls look like a ramshackle but heavily armed paramilitary group and are indistinguishable in costume from the Romans, except that the latter have special haircuts – mohawks died bright red on top. I found this a bit confusing and felt that it negated the theme of “occupiers versus occupied” which runs throughout the piece. This choice is probably intended to show the struggle as one between two rival groups in a polarized community. In the hands of the chorus the guns create a very menacing backgroup to several scenes, and of course the ending ends not by ritual burning, as in the original, but by firing squad.

The musical pyrotechnics do pose challenges for the staging, however, because an opera is not just a concert. It doesn’t work as music drama if the singers are just standing there belting out tunes. They also need to employ gestures and facial expressions to match the emotions expressed by the score and it can’t be too static. In this production the set is rather simple, and when I first saw it I assumed that it would be moved around a lot to create different locations, but that was only done to a limited extent. To compensate for the inflexible scenery, the chorus often provides a moving backdrop to the action. In the hands of the chorus the proliferation of guns create a very menacing backgroup to several scenes, and of course the ending ends not by ritual burning, as in the original, but by firing squad. The chorus was used very imaginatively, I’d say, not only to make up the numbers on stage, but also in their singing. I liked the idea of the chorus being split for some passages, leading one’s attention around the stage as the different groups gave voice.

I already mentioned Salome Jicia, but the other principals were also very good. Mario Chang (tenor) was a fine Pollione, William Guanbo Su a towering Oroveso with a rich bass and Siobhan Stagge as Adalgisa sang and acted beautifully. Despite some reservations about the staging, I thought this was a hugely enjoyable performance. Bellini has his critics, but I think the last part of Act II, the principals and chorus singing their hearts out to wonderful music, as the drama moves inexorably to its tragic conclusion, is one of the most intensely moving experiences in the entire operatic repertoire.

P.S. If you have 20 minutes to spare, listen to the Act II finale as performed by Callas here.