Twelve Years in The Dark!

When I logged onto WordPress today I received a message that it was the 12th anniversary of my registration with them as a blogger, which is when I took my first step into the blogosphere; that was way back on 15th September 2008.

I actually wrote my first post on the day I registered but unfortunately I didn’t really know what I was doing on my first day at blogging – no change there, then – and I didn’t actually manage to figure out how to publish this earth-shattering piece. It was only after I’d written my second post that I realized that the first one wasn’t actually visible to the general public because I hadn’t pressed the right buttons, so the two appear in the wrong order in my archive.

If you’re interested in statistics then, as of 13.00 Irish Summer Time Today today, I have published 5197 blog posts posts and have received 4,369,422 hits altogether; I get an average of just under 1000 per day. This varies in a very erratic fashion from day to day, but there has been a bit of a downward trend over the last few years, presumably because I’m getting older and more boring. The largest number of hits I have received in a single day is 8,864 (at the peak of the BICEP2 controversy).

There have been 35,313 comments published on here and 2,672,823 rejected by the spam filters. The vast majority of the rejected comments were from bots, but a small number have been removed for various violations, usually for abuse of some kind. And, yes, I do get to decide what is published: it is my blog!

While I am on the subject of comments, I’ll just repeat here the policy stated on the home page of this blog:

Feel free to comment on any of the posts on this blog but comments may be moderated; anonymous comments and any considered by me to be abusive will not be accepted. I do not necessarily endorse, support, sanction, encourage, verify or agree with the opinions or statements of any information or other content in the comments on this site and do not in any way guarantee their accuracy or reliability.

It does mean a lot to me to know that there are people who find my ramblings on this `shitty wordpress blog’ interesting enough to look at, or even read, and sometimes even to come back for more, so I’d like to take this opportunity to send my best wishes to all those who follow this blog and especially those who take the trouble to comment on it in such interesting and unpredictable ways!

The last twelve years have been eventful, to say the least, both personally and professionally. I started blogging not long after I’d moved into my house in Pontcanna, Cardiff. Since then I moved to Sussex, then back to Cardiff, and now to Ireland. More importantly we’ve seen the discovery of the Higgs Boson and gravitational waves, both of which resulted in Nobel Prizes, as did the studies of high-redshift supernovae. The Planck mission mission was launched, did its stuff, and came to a conclusion in this time too. Science has moved forward, even if there are many things in this world that seem to be going backwards.

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New Publication at the Open Journal of Astrophysics!

A day may come when I don’t write a blog post every time we publish a new paper in the Open Journal of Astrophysics, but it is not this day…

Today’s new publication is by Liliya Williams (of the University of Minnesota, Twin Cities) and David Zegeye of the University of Chicago and is entitled Two-component mass models of the lensing galaxy in the quadruply imaged supernova iPTF16geu.

Here is a screen grab of the overlay:

You can click on the image to make it larger should you wish to do so.

Incidentally, you may notice that Scholastica have added MathJax to the platform to render mathematical expressions in the abstract.

You can find the arXiv version of the paper here.

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Today’s Big Astronomy Announcement

Rumours have been circulating for a few days about a big astronomical discovery. Here is a video of the announcement:

Sorry, that’s the wrong video.

The actual announcement will take place live at 4pm BST here:

Until a few minutes ago I didn’t have a clue what this was about, but now I do…

Phone ship surprisingly detected in atmosphere of Venus (9)

If you would like to read more about this discovery then you can read the paper in Nature here. Several of the authors are former Cardiff colleagues, including first author Jane Greaves, as well as Annabel Cartwright and my former office mate Emily Drabek-Maunder. Congratulations to them on an exciting result!

P.S. Emily reminded me last night that I was present at the discussion with Jane that started this project, over four years ago. I remember them talking about phosphine but had no idea that it would lead to this!

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New Publication at the Open Journal of Astrophysics!

Another new paper  has been published in the Open Journal of Astrophysics! This is another for the folder marked Cosmology and Nongalactic Astrophysics and is entitled Low-scatter galaxy cluster mass proxies for the eROSITA all-sky survey.

The authors of this paper are Dominique Eckert of the University of Geneva, Alexis Finoguenov (Helsinki), Vittorio Ghirardini (MPE Garching), Sebastian Grandis (LMU), Florian Käfer (MPE Garching), Jeremy Sanders (MPE Garching) and Miriam Ramos-Ceja (MPE Garching).

For those of you unfamiliar with eROSITA, it is an X-ray instrument that was built at the Max Planck Institute for Extraterrestrial Physics, where several of the authors work.

Here is a screen grab of the overlay:

You can click on the image to make it larger should you wish to do so.

You can find the arXiv version of the paper here.

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R.I.P. Govind Swarup (1929-2020)

This morning I learnt the sad news of the passing of Professor Govind Swarup who died yesterday at the age of 91. Govind Swarup was a pioneer in radio astronomy, especially in India, and in particular was a driving force behind the construction of the Giant Metrewave Radio Telescope, and the establishment of a world-leading radioastronomy group, which is located about 80km North of Pune in Maharashtra. I remember meeting with him a couple of times during visits to Pune and was struck by his friendliness and unbounded enthusiasm for astrophysics.

I send my condolences to his family, friends and colleagues in India who I know will miss him enormously.

R. I. P. Govind Swarup (1929-2020).

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Littlewood on `the real point’ of lectures

We’re often challenged these days to defend the educational value of the lecture as opposed to other forms of delivery, especially with the restrictions on large lectures imposed by Covid-19. But this is not a new debate. The mathematician J.E. Littlewood felt necessary to defend the lecture as a medium of instruction (in the context of advanced mathematics) way back in 1926 in the Introduction to his book The Elements of the Theory of Real Functions.

(as quoted by G. Temple in his Inaugural Lecture as Sedleian Professor of Natural Philosophy at the University of Oxford in 1954 “The Classic and Romantic in Natural Philosophy”.)

Temple concluded his lecture with:

Classic perfection should be reserved for the monograph: the successful lecture is almost inevitably a romantic adventure. It is at once the grandeur and misery of a scientific classic that it says the last word: it is the charm of a scientific romance that it utters the first word, and thus opens the windows on a new world.

Modern textbooks do try to be more user-friendly than perhaps they were in Littlewood’s day, and they aren’t always “complete and accurate” either, but I think Littlewood is right in pointing out that they do often hide `the real point’ so students sometimes can’t see the wood for the trees. The value of lectures is not in trying to deliver masses of detail but to point out the important bits.

It seems apt to mention that the things I remember best from my undergraduate lectures at Cambridge are not what’s in my lecture notes – most of which I still have, incidentally – but some of the asides made by the lectures. In particular I remember Peter Scheuer who taught Electrodynamics & Relativity talking about his first experience of radio astronomy. He didn’t like electronics at all and wasn’t sure radio astronomy was for him, but someone – possibly Martin Ryle – reassured him by saying “All you need to know in order to do this is Ohm’s Law. But you need to know it bloody well.”

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Watch “Why the Universe is quite disappointing really – Episode 7” on YouTube

Back for Episode 7 of this series in which I explain how we can measure the strength of acoustic waves in early Universe using measurements of the cosmic microwave background, and how that leads to the conclusion that the Big Bang wasn’t as loud as you probably thought. You can read more about this here.

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Primordial Figures

I was rummaging around looking for some things related to a paper I’m struggling to finish before term starts and I found some vintage diagrams. They brought back a lot of memories of working on the textbook I wrote with Francesco Lucchin way back in the 1990s. In particular I remember how long it took to make these figures, when nowadays it would take a few minutes. In fact I’m thinking of setting this as a Computational Physics project for next year. These are not full computations either, just a simple fluid-based approach.

The curves show the evolution of fluctuations in both matter δ_m and radiation δ_r on a particular scale (i.e. a Fourier mode of given wavelength) defined as δ_m=δρ_m/ρ_m, etc.  The x-axis shows the cosmic scale factor, which represents the expansion of the Universe and in both cases the universe is flat, i.e. it has a critical density. The first graph shows a universe with only baryonic matter:

Notice the strongly coupled oscillations in matter and radiation until a scale factor of around 10^-3, corresponding to a redshift of a thousand or so, which is when matter and radiation decouple. The y-axis is logarithmic so the downward spikes represent zero points.

It is these oscillations which are responsible for the bumps and wiggles in the spectrum of the cosmic microwave background spectrum, as different Fourier modes arrive at the last scattering surface at a different phase of its oscillation. Of course going from the Figure above to the CMB fluctuation spectrum (see below) involves more calculations, and there is now a well-established machinery for doing these with full physical descriptions, but I think the above diagram makes the physical origin of these features clear.

The CMB power spectrum from Planck

The second diagram shows what happens if you add a third component called `X’ in the Figure below which we take to be cold non-baryonic matter. Because  this stuff doesn’t interact directly with radiation (while baryons do) it doesn’t participate in the oscillations but the density perturbations just carry on growing:

Notice too that at late times (i.e. after the baryonic matter and radiation have decoupled) the baryonic component grows much more quickly than in the first Figure. This is because, when released from the effect of the photon background, baryons start to feel the gravitational pull of the dark matter perturbations.

There’s nothing new in this of course – these Figures are thirty years old and similar were produced even earlier than that – but I still think pictures like these are pedagogically useful,

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New Publication at the Open Journal of Astrophysics!

So another new paper has been published in the Open Journal of Astrophysics! This one is in the folder marked Astrophysics of Galaxies and is entitled Massive Star Formation in Metal-Enriched Haloes at High Redshift. I should explain that “Metal” here is the astrophysicist’s definition which basically means anything heavier than hydrogen or helium: chemists may look away now.

The authors of this paper are John Regan (of the Department of Theoretical Physics at Maynooth University), Zoltán Haiman (Columbia), John Wise (Georgia Tech), Brian O’Shea (Michigan State) and Michael Norman (UCSD). And before anyone asks, no I don’t force members of staff in my Department to submit papers to the Open Journal of Astrophysics and yes I did stand aside from the Editorial process because of the institutional conflict.

Here is a screen grab of the overlay:

You can click on the image to make it larger should you wish to do so.

You can find the arXiv version of the paper here.

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Eddington in Cardiff 100 years ago today: the first proposal that stars are powered by fusion

Here’s a fascinating bit of astrophysics history by former Cardiff colleague Bernard Schutz: one hundred years ago today, Arthur Stanley Eddington gave a talk in Cardiff in which he, with great prescience, proposed the idea that stars might be powered by nuclear fusion.

The Rumbling Universe

One hundred years ago today, on 24 August 1920, with over 1000 people gathered in Cardiff for the annual meeting of the British Association, Arthur Eddington gave his address as the incoming president of the physical and mathematical sciences section. He elected to speak on the subject of the “Internal Constitution of the Stars”. When I first came across the text of the address last year (published in Nature in 1920), I was amazed to find as early as this such an insightful proposal that stars are powered by the synthesis of helium from hydrogen. But what really brought me up short was this sentence:

If, indeed, the sub-atomic energy in the stars is being freely used to maintain their great furnaces, it seems to bring a little nearer to fulfilment our dream of controlling this latent power for the well-being of the human race – or for…

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