Archive for the The Universe and Stuff Category

The Complex Heart of the Milky Way

Posted in Art, The Universe and Stuff with tags , , , on January 26, 2022 by telescoper

I couldn’t resist sharing this amazing radio image of the Galactic Centre made using the South African MeerKAT radio telescope:

Radio frequency electromagnetic radiation is able to penetrate the dust that permeates this region so can reveal what optical light can not. In particular you can see the very active region around the black hole at the centre of the Milky Way, bubbles caused by exploding stars and – most interesting of all – a number of magnetized filamentary structures.

It’s an extraordinarily beautiful picture made from a mosaic of 20 separate observations. In fact I like it so much I’ve cross-filed it in my “Art” folder.

For more information about this image at the science behind it, see here.

What’s the difference between Astronomy and Astrophysics?

Posted in Biographical, Education, Maynooth, The Universe and Stuff on January 24, 2022 by telescoper

I’ve been a bit busy today but I did notice at lunchtime that an old question has been going around on Twitter which gives me the excuse to post an old answer to it, what’s the difference between Astronomy and Astrophysics? This is something I’m asked quite often, and have blogged about before, but I thought I’d repeat it here for those who might stumble across it.

The Oxford English Dictionary gives the following primary definition for astronomy:

The science which treats of the constitution, relative positions, and motions of the heavenly bodies; that is, of all the bodies in the material universe outside of the earth, as well as of the earth itself in its relations to them.

Astrophysics, on the other hand, is described as

That branch of astronomy which treats of the physical or chemical properties of the celestial bodies.

So astrophysics is regarded as a subset of astronomy which is primarily concerned with understanding the properties of stars and galaxies, rather than just measuring their positions and motions.

It is possible to assign a fairly precise date when astrophysics first came into use in English because, at least in the early years of the subject, it was almost exclusively associated with astronomical spectroscopy. Indeed the OED gives the following text as the first occurrence of astrophysics, in 1869:

As a subject for the investigations of the astro-physicist, the examination of the luminous spectras of the heavenly bodies has proved a remarkably fruitful one

The scientific analysis of astronomical spectra began with a paper by   William Hyde Wollaston in the Philosophical Transactions of the Royal Society Vol. 102, p. 378, 1802. He was the first person to notice the presence of dark bands in the optical spectrum of the Sun. These bands were subsequently analysed in great detail by Joseph von Fraunhofer in a paper published in 1814 and are now usually known as Fraunhofer lines.  Technical difficulties  made it impossible to obtain spectra of stars other than the Sun for a considerable time, but  William Huggins finally succeeded in 1864. A drawing of his pioneering spectroscope is shown below.

Meanwhile, fundamental work by Gustav Kirchoff and Robert Bunsen had been helping  to establish an understanding of the spectra produced by hot gases.  The identification of features in the Sun’s spectrum  with similar lines produced in laboratory experiments led to a breakthrough in our understanding of the Universe whose importance shouldn’t be underestimated. The Sun and stars were inaccessible to direct experimental test during the 19th Century (as they are now). But spectroscopy now made it possible to gather evidence about their chemical composition as well as physical properties. Most importantly, spectroscopy provided definitive evidence that the Sun wasn’t made of some kind of exotic unknowable celestial material, but of the same kind of stuff (mainly Hydrogen) that could be studied on Earth.  This realization opened the possibility of applying the physical understanding gained from small-scale experiments to the largest scale phenomena that could be seen. The science of astrophysics was born.

One of the leading journals in which professional astronomers and astrophysicists publish their research is called the Astrophysical Journal, which was founded in 1895 and is still going strong. The central importance of the (still) young field of spectroscopy can be appreciated from the subtitle given to the journal:

Initially the branch of physics most important to astrophysics was atomic physics since the lines in optical spectra are produced by electrons jumping between different atomic energy levels. Spectroscopy of course remains a key weapon in the astrophysicist’s arsenal but nowadays the term astrophysics is taken to mean any application of physical laws to astronomical objects. Over the years, astrophysics has therefore gradually incorporated nuclear and particle physics as well as thermodynamics, relativity and just about every other branch of physics you can think of.

I realize, however, that this  isn’t really the answer to the question that potential students want to ask. What they (probably) want to know is what is the difference between undergraduate courses called Astronomy and those called Astrophysics? The answer to this one depends very much on where you want to study. Generally speaking the differences are in fact quite minimal. You probably do a bit more theory in an Astrophysics course than an Astronomy course, for example. Your final-year project might have to be observational or instrumental if you do Astronomy, but might be theoretical in Astrophysics.  If you compare the complete list of modules to be taken, however, the difference will be very small.

Over the last twenty years or so, most Physics departments in the United Kingdom have acquired some form of research group in astronomy or astrophysics and have started to offer undergraduate degrees with some astronomical or astrophysical content. My only advice to prospective students wanting to find which course is for them is to look at the list of modules and projects likely to be offered. You’re unlikely to find the name of the course itself to be very helpful in making a choice.

To confuse things further, here in Maynooth there is a degree programme called Physics with Astrophysics which is taught primarily by the Department of Experimental Physics and has a heavy focus on observational techniques. If students want to do the interesting theoretical bits of Astrophysics, such as black holes and general relativity, they have to choose  options with the Department of Theoretical Physics.  As a theoretical astrophysicist I feel a bit frustrated by this.

One of the things that drew me into astrophysics as a discipline is that it involves such a wide range of techniques and applications, putting apparently esoteric things together in interesting ways to develop a theoretical understanding of a complicated phenomenon. I only had a very limited opportunity to study astrophysics during my first degree as I specialized in Theoretical Physics.  This wasn’t just a feature of Cambridge. The attitude in most Universities in those days was that you had to learn all the physics before applying it to astronomy. Over the years this has changed, and most departments offer some astronomy right from Year 1.

I think this change has been for the better because I think the astronomical setting provides a very exciting context to learn physics. If you want to understand, say, the structure of the Sun you have to include atomic physics, nuclear physics, gravity, thermodynamics, radiative transfer and hydrostatics all at the same time. This sort of thing makes astrophysics a good subject for developing synthetic skills while more traditional physics teaching focusses almost exclusively on analytical skills.

I hope this clarifies the situation.

Memories of Perugia

Posted in Biographical, The Universe and Stuff with tags , on January 23, 2022 by telescoper

My friend and colleague Vicent Martínez sent me this picture which dates from the spring of 1988.

Picture credit: Vicent Martinez

It took me a while to figure out where it was taken but I finally came to the conclusion that it was in Perugia (the University thereof) in Italy at a small workshop organized there by Silvio Bonometto. If memory serves that room was called the Aula Mussolini

I am on the far left (looking deranged) and talking to Alain Blanchard (with the long black hair). In between us is Vincent Icke. Further along the same row you can see Dennis Sciama, who is sadly no longer with us, and John Miller. In the middle looking at the camera is Rien van de Weijgaert. Just behind me is Bernard Jones. I guess Vicent must have taken the picture!

You can find this and other pictures from this bygone era here.

Yes, I know it’s very white and very male. Meetings tended to be like that in those days.

Incidentally 1988 was the year that I finished my DPhil thesis so I was still a graduate student at the time of this meeting. I think I gave a talk but can’t remember what it was about! In fact I don’t remember much about that meeting except for the splendid lunch that happened at the end. We took a coach trip to a magnificent Castello in the country and were treated to a lavish banquet of many courses. As luck would have it I sat next to Dennis Sciama at the meal, which I enjoyed greatly. Dennis was my academic grandfather (i.e. he supervised my supervisor). He was a lovely gracious man as well as hugely knowledgeable about a wide range of things, wonderful to talk to, and very generous with his time. He was also teetotal, so when they came to fill up his glass he gave it to me so I had a double wine ration, and a single ration would have been a lot!

If I recall correctly the coach trip also took in quick visits to the towns of Cortona and Arezzo.

Anyway, seeing that picture sent me a bit down memory lane during which I opened up a box of old photographs to find some more of Perugia. That meeting in 1988 was the first time I’d visited that ancient and beautiful place but I’ve been back a few times since then and on one occasion took a few snaps as I wandered round. I thought black-and-white would capture the atmosphere of the place. You can decide whether I was right!

The first picture is of the main square (Piazza IV Novembre) and the second the famous Etruscan Arch, which dates from pre-Roman times, emphasizing how ancient this place is! The town is perched on top of a steep-sided hill so it’s quite hard work getting around on foot but well worth exploring.

R.I.P. Sir David Cox (1924-2022)

Posted in Biographical, mathematics, The Universe and Stuff with tags , , , , on January 21, 2022 by telescoper

I was saddened to hear a few days ago that the eminent statistician David Cox has passed away at the age of 97. I didn’t know Professor Cox personally – I met him only once, at a joint astronomy-statistics meeting at (I think) the Royal Astronomical Society back in the day – but I learnt a huge amount from books he co-wrote, despite the fact that he was of the frequentist persuasion. Three examples from my bookshelf are shown above.

I started my PhD DPhil in 1985 with virtually no formal study of statistics under my belt so I had to follow a steep learning curve and I was helped enormously by these books. I bought the book on Point Processes so as to understand some of the ideas being applied to galaxy clustering. It’s only a short book but it’s crammed with interesting ideas. Cox & Miller on Stochastic Processes is likewise a classic.

I know I’m not the only person in astrophysics whose career has been influenced by David Cox and I’m sure there are many other disciplines who have benefitted from his knowledge.

Among many other awards, David Cox was elected a Fellow of the Royal Society in 1973 and knighted in 1985.

Rest in peace Sir David Cox (1924-2022)

New Publication at the Open Journal of Astrophysics

Posted in Open Access, The Universe and Stuff with tags , , , , on January 18, 2022 by telescoper

It’s a New Year and therefore a new Volume of the Open Journal of Astrophysics and it’s time to announce the first publication in it! This one is the 1st paper in Volume 5 (2022) and the 49th in all.

The latest publication is entitled Validating Synthetic Galaxy Catalogs for Dark Energy Science in the LSST Era and is written by Eve Kovacs of Argonne National Laboratory and 38 others on behalf of the LSST Dark Energy Science Collaboration.

Here is a screen grab of the overlay which includes the abstract:

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. This is another one for the Cosmology and Nongalactic Astrophysics folder, which remains the most popular category so far on the Open Journal of Astrophysics site.

There is a little bit of a backlog in OJAp Towers owing to the Christmas break as some authors have been on leave and not doing their revisions, so I’d anticipate a few more papers in the next few weeks.

Congratulations to the 2022 RAS Award Winners!

Posted in The Universe and Stuff with tags , , , , , on January 15, 2022 by telescoper

Given all the doom and gloom going around I thought I’d take the opportunity to share some good news and also offer my public congratulations to the all the winners of medals and awards announced yesterday by the Royal Astronomical Society. Let me draw particular attention to the following subset, purely on the grounds that I know them and their work personally (and because they’ve all either been mentioned on this blog recently and/or been known to read it from time to time and/or have recently published in the Open Journal of Astrophysics and/or are on the Editorial Board thereof).

First, the Gold Medal goes to Professor George Efstathiou of Cambridge University a true giant of cosmology (metaphorically speaking of course – I’m actually taller than him):

I’m looking forward to George receiving his medal so he can tell us what kind of chocolate is inside.

Second, Professor Alan Heavens of South Kensington Technical College Imperial College London who gets the Eddington Medal:

I should mention that among many other things Alan has worked extensively on the application of Bayesian methods to cosmological data.

Third, Professor Catherine Heymans of Edinburgh, Astronomer Royal for Scotland, wins the Herschel medal;

Catherine was actually a PhD student supervised by Alan Heavens back in the day. I wonder if this is the first time that a PhD student/supervisor combination has won RAS medals in the same year?

Correction: I’m now told that Catherine actually did her PhD in Oxford supervised by Lance Miller so I withdraw the question.

And last but by no means least we have Professor Pedro Gil Ferreira who will give this year’s Gerald Whitrow lecture:

Two interesting facts about Pedro: (i) a direct English translation of “Pedro Ferreira” would be “Peter Smith”; and (ii) he is a member of the Editorial Board of the Open Journal of Astrophysics.

Congratulations to them and indeed to all the winners of awards and medals, a complete list of whom may be found here.

P.S. It suddenly struck me when I saw the announcements yesterday evening that it’s now two years since I last attended the RAS Ordinary Meeting in person or the RAS Club Dinner. Let’s hope these can start again reasonably soon.

The Largest Map of the Universe

Posted in The Universe and Stuff with tags , , , on January 14, 2022 by telescoper

Now I’m going to have to update the bit of my popular talks (e.g this one) about `Mapping the Universe’!

After just seven months of operations of the Dark Energy Spectroscopic Instrument (DESI) we now have the largest galaxy redshift survey – and it’s only about 10% of the way through its 5-year programme. Currently mapping the positions of about 7.5 million galaxies, the map will contain over 35 million by the time the survey is complete. Even now it is larger than all previous spectroscopic galaxy redshift surveys put together. The speed of DESI is accounted for by its use of 5000 robotically-positioned fibre-optic cables that can generate spectra of thousands of galaxy from a single pointing of the 4-m telescope on which it is mounted.

You can read more about the latest results from DESI here. I’ll just whet your appetite with this groovy animated picture:

DESI’s three-dimensional “CT scan” of the Universe. We are at in the lower left, looking out over 5 billion light years in the direction of the constellation Virgo. As the video progresses, the perspective sweeps toward the constellation Bootes. Each colored point represents a galaxy; gravity has pulled the galaxies into a “cosmic web” of dense clusters, filaments and voids. (Credit: D. Schlegel/Berkeley Lab using data from DESI)

The twinkling effect arises from the fact that you are viewing different thin slices through the 3D distribution. The dark sections that appear and disappear from time to time are just bits not yet included in the survey.

For those of you not familiar with astronomical distance measurements, 1500 megaparsecs = 1.5 Gigaparsecs = 4.5 billion light years (approximately), so this map is not only mapping the spatial distribution of galaxies but also how this distribution has evolved with cosmic time over billions of years.

ERC Starting Grant Statistics

Posted in Politics, Science Politics, The Universe and Stuff with tags , , , , , on January 10, 2022 by telescoper

Today the European Research Council (ERC) announced the first round of winners of Starting Grants under the new Horizon Europe programme. The results make for interesting reading. Some 397 grants were awarded worth a total of €619 million, i.e. about €1.5 million each on average, all intended for researchers in the early stages of their careers. A complete list of award winners can be found in this PDF document. Congratulations to all of them!

Here is the breakdown by host country:

You will see that Ireland has secured 8 (half in social sciences & humanities, and half in science). That’s not bad for a small country, and is comparable with Denmark, Norway and Finland. The only two funded in Physical Sciences & Engineering in Ireland are both at the University of Limerick.

The big shock, however, is that the number of grants to be hosted in the UK is down sharply on previous Starter Grant rounds. In previous years that I can remember the UK was at the top of the awards table. Now top spot goes to Germany, with the UK in third place, only just above the Netherlands. I wonder what the reason could be for that?

You might be surprised that the UK is listed at all because it is not in the EU has not signed an association agreement with the European Union. Switzerland, also not in the EU, has been awarded 28 grants but these are not eligible for funding because negotiations on association have ended without a signature. According to the ERC website:

As a result, host institutions established in Switzerland are not eligible for funding. Exceptionally for this call, since it was already closed before the termination of the negotiations between the EU and Switzerland, the proposals submitted with Swiss host institutions and which have been selected for funding may remain eligible if their host institution is replaced with a legal entity established in an eligible country.

This looks like a cue for other institutions to start poaching! Israel and Norway are non-EU countries have agreements in place.

The situation with the UK, as far as I understand it, is that negotiations towards an association agreement are currently snarled up with issues surrounding the Northern Ireland Protocol component of the UK’s withdrawal agreement from the European Union. If an agreement is signed before contracts have to be issued (in April) then the grants to UK institutions will be funded by the EU. If not then not.

In addition, successful applicants established in a country in the process of associating to Horizon Europe will not be treated as established in an associated country if the association agreement does not apply by the time of the signature of the grant agreement. 

In this case, however, the UK Government will fund these through the UKRI budget. So they say.

On the other hand, these grants are portable and some winners may decided to change host institution to avoid any uncertainty. Cue some more poaching?

Another thing that is striking is that although 46 UK institutions are intended hosts for such funding, only 12 of the grantees have UK nationality.

It follows that many of the UK’s grantees are from elsewhere, either in the EU or outside. It is possible under this scheme for awardees to relocate to institutions in member countries from non-member countries, which accounts for the large number of “Others” in the plot.

Notice the opposite applies to Italy: there are 58 Italian grantees but only 28 grants will be hosted in Italy.

Here is the breakdown by gender:

Anyway, you can read more about the statistics in this PDF document here.

Webb Deployment

Posted in Biographical, The Universe and Stuff with tags on January 8, 2022 by telescoper

I’ve been busy all afternoon supervising an online examination and I’m now about to cook my dinner, which means I haven’t got time to post anything much but I will pass on the very welcome news that the James Webb Space Telescope has now completed the lengthy sequence of operations that were required to deploy a large sunshield, the primary and secondary mirrors and other bits and bobs needed to turn it into a proper observatory rather than just a basket of deployables. The whole thing should now look something like this:

Artists impression of Webb (with, by the look of it, a bit of the Cosmic Web)

There were over 300 potential single-point failures in this sequence so these last couple of weeks have been as stressful as the launch. Now commissioning work can begin.

This all gives me the excuse to have a celebratory drink just like I did on Christmas Day. Cheers!

A Piece of Euclid

Posted in Biographical, Maynooth, The Universe and Stuff with tags , , on January 6, 2022 by telescoper

Fame at last! A colleague from the Department of Theoretical Physics at Maynooth University told me the above piece appeared in today’s Irish Times so I rushed out and bought the paper. My rapture was rapidly modified however when I discovered that my name was given incorrectly (as Cole instead of Coles), but that was to some extent offset by the amusement it would give my colleagues to see me described as an “Experiment Physicist”. These two slips are now corrected in the online version of the article which you can find here.

I was quite surprised by the sudden appearance of the article today because I spoke to the writer, Seán Duke, about Euclid well over a year ago (May 2020). That’s the reason that some things are a bit out of date. For example, the launch of Euclid will now not take place until the first quarter of 2023. Also the piece states that the largest telescope in space is the Hubble Space Telescope (HST) which is no longer the case (as of Christmas Day 2021…).

I’ll leave it as an exercise for the student to spot any other errors. Please feel free to point them out through the Comments Box. If you’re not banned, that is…