Maynooth University Library Cat, photographed yesterday by Joost Slingerland.
Yesterday morning final-year students theoretical physics students sat my first examination of the session, on Advanced Electromagnetism, and tomorrow another group will take my second, on Computational Physics 1. I collected the first scripts from the Exam Hall at the end of the examination at 11.30 and have actually finished correcting them. I don’t think I’ll come in tomorrow morning though. Correcting the second batch can wait until Monday. That doesn’t mean I get a break though because I still have to complete grading the Computational Physics Projects. It does mean, however, that I’ll probably be finished with examination marking for this session by the end of next week, in good time for the Exam Boards in June.
That won’t mean that I’m finished with examination matters for the year; I’ll have four repeat examinations to grade in August. When those are done, however, I won’t have to do any further marking of examinations or anything else to do with teaching for a whole year. My sabbatical starts on 1st September.
Meanwhile, Maynooth University Library Cat, has been patrolling the area in front of the Library, which is quite busy these days with students doing last-minute revision in the study spaces there. By the end of next week the examinations will be over, most students will have departed for the summer, many staff will be at home marking scripts, and campus will be much quieter.
Fanciful “artist’s impression” of a Neutron Star – Black Hole merger (from last time).
It seems that the engineering data ahead of the imminent observing run from the newly refurbished LIGO gravitational wave observatory has just triggered an alert for astronomers to look for an electromagnetic counterpart. The code number for this candidate event is S230518h. If confirmed this could very well be another Neutron-Star – Black Hole merger event. The search area is rather large, with the 90% probability region being about 1002 square degrees on the sky:
I’m reminded about the excitement surrounding the first Neutron Star merger way back in 2017. In fact, rumours started to spread via this blog as people outside the LIGO/transient source community used a comments thread here to share information of where telescopes were looking. Those were the days. Was that really 6 years ago?
It’s time to announce yet another new paper at the Open Journal of Astrophysics. This one was published yesterday (17th May).
The latest paper is the 17th paper so far in Volume 6 (2023) and the 82nd in all. With this one we have now published as many papers so far in 2023 as we did in all of last year. With significantly less than half the year gone, and a large number of papers in the pipeline, I think it’s quite likely we will exceed a total of 100 papers by the end of 2023. How’s that for cosmic acceleration?
The primary classification for this paper is Instrumentation and Methods for Astrophysics and its title is “Deep-field Metacalibration”. This article describes a technique that reduces the pixel noise in estimators of weak gravitational lensing shear signals by using a deeper imaging survey for calibration.
The authors are Zhuoqi (“Jackie”) Zhang (University of Chicago, IL, USA), Erin Sheldon (Brookhaven National Laboratory, NY, USA), and Matthew Becker (Argonne National Laborary, IL, USA).
Here is a screen grab of the overlay which includes the abstract:
You can click on the image of the overlay to make it larger should you wish to do so. You can find the officially accepted version of the paper, along with all other astrophysics and cosmology research papers worth reading, on the arXiv here.
I just remembered that today is May 17th which means that it is International Day Against Homophobia Transphobia and Biphobia, This is a worldwide celebration of sexual and gender diversities and a chance to show solidarity against bigotry and intolerance.
A video circulating today on social media in Ireland showing a teenager being beaten up because he is gay reminds us that we need this now more than ever; there’s a news report here. I hope the culprits are brought to justice. The rising tide of violence and discrimination against LGBTQI+ individuals is encouraged by those who spread poisonous rhetoric in the media and online.
As the launch of the European Space Agency’s Euclid mission approaches, though we don’t know official launch date yet, the associated publicity machines are ramping up for the big occasion. The latest bit of merch is the Euclid Launch Kit.
Sadly, this does not allow you to build your own Falcon 9 launcher which is what I inferred from the name. What it is is an interactive PDF file that allows you to navigate around and learn things about the satellite, its orbit, its instruments and the science case. I think it’s pretty good. You can download it here. It’s over 100 MB though, so beware if you have a very slow connection.
To whet your appetite, here some graphics extracted from the launch kit. You can click on the tiles to make them bigger.
In my capacity as managing editor of the Open Journal of Astrophysics I’ve received a few emails recently disagreeing with our policy of asking authors to submit their papers to the arXiv before submitting them to OJAp. Before reflecting on the wider issue, let me just point out that we don’t actually require papers to on the arXiv first. It is possible to submit a PDF directly to the Scholastica platform. We do however say in our For Authors page:
We strongly encourage authors to submit in the manner described above (i.e. on the arXiv first). We can receive and review papers submitted directly to this platform but since the final version must be on the arXiv in order to be published we feel it is far better to submit it there first in order to establish that it is on an appropriate topic for this journal.
Looking back over the 81 papers we have published, only a handful were submitted directly to the platform; the vast majority were put on the arXiv first.
This behaviour is in some sense a continuation of a very old practice in astrophysics. I can’t resist sharing this, one of the interesting astronomical curiosities I’ve acquired over the years, which is a preprint of the classic work of Burbidge, Burbidge, Fowler and Hoyle in 1957 (a paper usually referred to as B2FH after the initials of its authors), which is such an important contribution to the literature that it has its own wikipedia page.
Younger readers will probably not realize that preprints were not always produced in the electronic form they are today. We all used to make large numbers of these and post them at great expense to (potentially) interested colleagues before publication in order to get comments. That was extremely useful because a paper could take over a year to be published after being refereed for a journal: that’s too long a timescale when a PhD or PDRA position is only a few years in duration. The first papers I was given to read as a new graduate student in 1985 were all preprints that were not published until well into the following year. In some cases I had more or less figured out what they were about by the time they appeared in a journal!
The B2FH paper was published in 1957 but the practice of circulating preprints persisted well into the 1990s. Usually these were produced by institutions with a distinctive design, logo, etc which gave them a professional look, which made it easier to distinguish `serious’ papers from crank material (which was also in circulation). This also suggested that some internal refereeing inside an institution had taken place before an “official” preprint was produced and this lending it an air of trustworthiness. Smaller institutions couldn’t afford all this, so were somewhat excluded from the preprint business.
With the arrival of the arXiv the practice of circulating hard copies of preprints in astrophysics gradually died out, to be replaced by ever-increasing numbers of electronic articles. The arXiv does have some gatekeeping – in the sense there are some controls on who can deposit a preprint there – but it is far easier to circulate a preprint now than it was.
It is still the case that big institutions and collaborations insist on quite strict internal refereeing before publishing a preprint – and some even insist on waiting for a paper to be accepted by a journal before adding it to the arXiv – but there’s no denying that among the wheat there is quite a lot of chaff, some of which attracts media coverage that it does not deserve. It must be admitted, however, that the same can be said of some papers that have passed peer review and appeared in high-profile journals! No system that is operated by human beings will ever be flawless, and peer review is no exception.
Nowadays, in astrophysics, the single most important point of access to scientific literature is through the arXiv, which is why the Open Journal of Astrophysics was set up as an overlay journal to provide a level of rigorous peer review for preprints, not only to provide quality control but also to improve papers through the editorial process. In fact, I think the latter is more important than the former.
It’s time to announce yet another new paper at the Open Journal of Astrophysics. In fact it’s a little overdue, because we published this one on Friday 12th May, but I just got round to posting it on here.
The authors are Erin Sheldon (Brookhaven National Laboratory, NY, USA), Matthew Becker (Argonne National Laborary, IL, USA), Michael Jarvis (University of Pennsylvania, PA) and Robert Armstrong (Lawrence Livermore National Laboratory, CA) – all in the USA – and the LSST Dark Energy Science Collaboration, who have published a significant number of publications with OJAp. In fact, we’ll have another one in a day or two.
Here is a screen grab of the overlay which includes the abstract:
You can click on the image of the overlay to make it larger should you wish to do so. You can find the officially accepted version of the paper, along with all other astrophysics and cosmology research papers worth reading, on the arXiv here
It’s been too long since I last posted one of the cosmology talks curated on YouTube by Sean Hotchkiss so I will endeavour to put that right by posting one today.
In this video, Jeongin Moon, David Valcin and Christoph Saulder talk about the first cosmologically relevant results from DESI (the Dark Energy Spectroscopic Instrument), including the first detection of the BAOs (Baryon Acoustic Oscillations) therefrom. It’s pretty impressive for a first detection with only two months worth of data, so the final result with the full data set should be spectacular!
You can of course read the paper related to these results (by Moon et al.) on the arXiv here.
After last night’s Eurovision 2023 extravaganza I thought I’d work off my hangover by summarizing the voting. The vote is split into 50% jury votes and 50% televotes from audiences sitting at home, drunk. It’s perhaps worth mentioning that the juries do their scores based on the dress rehearsals on Friday so they are not based on the performances the viewers see.
Each country/jury has 58 points to award, shared among 10 countries: 1-8, 10 and 12 for the top score. Countries that didn’t make it to the final (e.g. Ireland) also get to vote. For the televotes only there is also a “rest-of-the-world” vote for non-Eurovision countries.
This system can deliver very harsh results because only 10 songs can get points from a given source. It’s possible to be judged the 11th best across the board and score nil!
Here are the final scores in a table:
Rank
Country
Overall
Televotes
Jury
Diff
Rank Diff
1
Sweden
583
243
340
+97
+1
2
Finland
526
376
150
-226
-1
3
Israel
362
185
177
-8
+3
4
Italy
350
174
176
+2
+3
5
Norway
268
216
52
-168
-14
6
Ukraine
243
189
54
-145
-11
7
Belgium
182
55
127
+72
+5
8.
Estonia
168
22
146
+124
+14
9.
Australia
151
21
130
+109
+14
10.
Czechia
129
35
94
+59
+7
11.
Lithuania
127
46
81
+35
+4
12.
Cyprus
126
58
68
+10
-2
13.
Croatia
123
112
11
-101
-18
14.
Armenia
122
53
69
+16
+1
15.
Austria
120
16
104
+88
+13
16.
France
104
50
54
+4
-2
17.
Spain
100
5
95
+90
+17
18.
Moldova
96
76
20
-56
-11
19.
Poland
93
81
12
-69
-16
20.
Switzerland
92
31
61
+30
+4
21.
Slovenia
78
45
33
-12
-3
22.
Albania
76
59
17
-42
-11
23.
Portugal
59
16
43
+27
+4
24.
Serbia
30
16
14
+2
0
25.
United Kingdom
24
9
22
+13
0
26.
Germany
18
15
3
-12
-2
Final Scores by country in Eurovision 2023 showing the breakdown into televotes and jury votes, together with the difference in numerical scores awarded and difference in ranking based on jury votes rather than televotes, e.g. Albania scored 42 fewer points on the jury votes and would have been 11 places higher based just on televotes than just on jury votes.
Going into the last allocation of televotes, Finland were in in the lead thanks to their own huge televote, but Sweden managed to win despite a lower televote allocation because of their huge score on the jury votes. Had the scores been based on the jury votes alone, Sweden would have won by a mile, and if only on the televotes Finland would have won. Anyway, rules is rules…
There are some interestingly odd features in the above dataset. For example, Switzerland ranked 20th overall, but were ranked 18th and 14th by televotes and jury votes respectively. There are also cases in which a higher score in one set of votes leads to a lower rank, and vice-versa. Croatia were hammered by the jury votes, ranking 25th out of 26 on that basis but would have been 7th based on televotes alone; hence their -18 in the last column. A similar fate befell Norway. By contrast, Spain were last (26th) on the televotes but placed 9th in the pecking order by the juries; they ended up in 17th place.
Anyway, you can see that there are considerable differences between the scores and ranks based on the public vote and the jury votes. I have therefore deployed my vast knowledge of statistics to calculate the Spearman Rank Correlation Coefficient between the ranks based on televotes only and based on jury votes only. The result is 0.26. Using my trusty statistical tables, noting that n=26, and wearing a frequentist hat for simplicity, I find that there is no significant evidence for correlation between the two sets of ranks. I can’t say I’m surprised.
The apparent randomness of the scoring process introduces a considerable amount of churn into the system, as demonstrated by Mel Giedroyc in this, the iconic image of last night’s events.
At least I think that’s what she’s doing…
Anyway, for the record, I should say that my favourite three songs were Albania (22nd), Portugal (23rd) and Austria (15th). Maybe one day I’ll pick a song that makes it onto the left-hand half of the screen!
P.S. Eurovision 2024 will be in Sweden, which is nice because it will be the 50th anniversary of ABBA winning with Waterloo. I’ll never tire of boring people with the fact that a mere 15 years after ABBA won, I walked across the very same stage at the Brighton Centre to collect my doctorate from Sussex University…
I haven’t had time to write much about astrophysics and cosmology recently, so this morning I back a few days through the arXiv – where every research paper worth reading in these fields can be found – and found a fascinating paper by Kelly et al. about the gravitational lensing of a supernova known as SN Refsdal after the pioneer of gravitational lensing, Sfur Refsdal. When first observed in 2014 this supernova was observed as four images produced by the gravitational lensing of light from the supernova through a massive cluster of galaxies, a phenomenon known as an Einstein Cross.
Lens modellers quickly got to work on this system and concluded that two further images should exist. Given the difference in light travel times for lensed paths and the relatively short lifetime of a supernova, neither would occur at the same time as the four original ones. One image would have been observed at some point in the 1990s, had anyone been looking, but that wasn’t the case. However, another was predicted to occur in 2015 and that was observed. I call it Refsdal’s Ghost because of the French word revenant, which means a ghost but also someone who returns after a long absence. Anyway, the revenant is marked SX in the image below (obtained from here). The unobserved image is SY and the four originals S1-S4.
Multiple images of a point source a in a system such as this, with measured time delays, provide theorists with a great deal of information they can use to model the distribution of mass inside the cluster, including its physical size. That in turn allows one to measure its distance. With a measurement of redshift, this allows one to determine the Hubble Constant.
The gravitationally lensed Supernova Refsdal appeared in multiple images, produced through gravitational lensing by a massive foreground galaxy cluster. After the supernova appeared in 2014, lens models of the galaxy cluster predicted an additional image of the supernova would appear in 2015, which was subsequently observed. We use the time delays between the images to perform a blinded measurement of the expansion rate of the Universe, quantified by the Hubble constant (H0). Using eight cluster lens models, we infer H0 = 64.8 +4.4-4.3 km / s / Mpc, where Mpc is the megaparsec. Using the two models most consistent with the observations, we find H0 = 66.6 +4.1-3.3 km / s / Mpc. The observations are best reproduced by models that assign dark-matter halos to individual galaxies and the overall cluster.
Anyone who has been following developments in cosmology knows that there is currently some “tension” over different measurements of the Hubble constant, as illustrated in this figure (which is slightly dated but which makes the point):
There is some uncertainty of course, but it is interesting that the Kelly et al. measurement aligns with most of what are called the “early” measurements in this plot. As I have mentioned before, though, there is another common factor in the “early” measurements, which is that they are based on geometrical distances obtained from angular distances whereas most of the others are based on luminosity. If the Hubble tension were to resolve into a differences between these two types of measure then it would be of fundamental importance to cosmology. At present, however, there is nowhere near enough evidence to be sure one way or the other.
The views presented here are personal and not necessarily those of my employer (or anyone else for that matter).
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In the Dark 