Archive for the Astrohype Category

Today’s Big Astronomy Announcement

Posted in Astrohype, Cardiff, The Universe and Stuff with tags , , on September 14, 2020 by telescoper

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!

Finding the Lost Baryons

Posted in Astrohype, The Universe and Stuff with tags , , , , , on June 3, 2020 by telescoper

Taking a break from examination marking I thought I’d post a comment on a recent paper in Nature which you can find on the arXiv here; see also a report here.

The paper, entitled A census of baryons in the Universe from localized fast radio bursts, is an important one which does seem to resolve a longstanding question often called the missing baryon problem. In a nutshell, the problem is that the density of baryons suggested by cosmological considerations – specifically the element abundances produced by Big Bang nucleosynthesis and the cosmic microwave background (CMB) – was, until recently, rather higher than that which has been observed by astrophysical measurements; by `baryonic material’ I mean basically protons and neutrons (whether or not they are in atomic nuclei).

In the framework of the standard cosmological model, The density of baryonic matter (denoted `Ordinary Matter’ in the following figure) contributes only around 5% of the overall mass-energy budget of the Universe:

The first thing to stress is that this paper says nothing about the `Dark Matter’ which, according to the standard model, makes up about 27% of the pie and which cannot be in the form of baryons if the CMB and nucleosynthesis measurements are correct. If it were baryonic it would participate in nuclear reactions and mess up the light element abundances and also interact with photons in such a way as to change the fluctuation spectrum of the cosmic microwave background. Having said that, `dark’ is better adjective to use for hidden baryons than it is for non-baryonic matter, as baryons can absorb light. Non-baryonic matter isn’t really dark, it’s transparent because it doesn’t interact at all with electromagnetic radiation. We are however in the dark about it.

Note that the total density of dark + ordinary matter is about 32%, just what George Ellis and I concluded way back in 1994.

We can be much more certain about baryons actually existing than we can about dark matter because. For one thing, we are made of them. It has, however, been known for ages that the total density of directly visible baryons (ie those associated with stars and galaxies) is much lower than this figure, leading to the conclusion that some of the baryons predicted by cosmologists must be in some invisible form(s). Some, for example, is found by X-ray emissions in dense galaxy clusters, but this component is still inadequate to account for all the missing matter.

It has been suspected for some time that the hidden baryons probably inhabit a diffuse Warm-Hot Component of the Intergalactic Medium which, according to simulations of structure formation, traces its own form of the cosmic web we see in the distribution of galaxies:

The diffuse state and inhomogeneous nature of this intergalactic medium makes it difficult to detect, as explained in the abstract of the paper, but adding a relatively new technique involving fast radio bursts to probe the distribution of matter along the line of sight to the observer, it seems that it has now brought out into the open:

Now the inventory of observed baryons matches the 5% figure we cosmologists always knew it would be, and all is well with the world!

P. S. I was informed on Twitter after posting this that there was a paper on this topic in Nature a couple of years ago the last sentence of the abstract of which reads:

We conclude that the missing baryons have been found.

What are scientific papers for?

Posted in Astrohype, Open Access with tags , , on May 30, 2020 by telescoper

Writing scientific papers and publishing them in academic journals is an essential part of the activity of a researcher. ‘Publish or perish’ is truer now than ever, and an extensive publication list is essential for anyone wanting to have a career in science.

But what are these papers actually for? What purpose do they serve?

I can think of two main purposes (which aren’t entirely mutually exclusive): one is to disseminate knowledge and ideas; the other is to confer status on the author(s) .

The academic journal began hundreds of years ago with the aim of achieving the former through distribution of articles in print form. Nowadays the distribution of research results is achieved much less expensively largely through online means. Nevertheless, journals still exist (largely, as I see it, to provide editorial input and organise peer review) .

Alongside this there is the practice of using articles as a measure of the ‘quality’ of an author. Papers in certain ‘prestigious’ ‘high impact’ journals are deemed important because they are indicators of status, like epaulettes on a uniform, and bibliometric data, especially citation counts, often seem to be more important than the articles themselves.

I thought it was just me getting cynical in my old age but a number of younger scientists I know have told me that the only reason they can see for writing papers is because you need to do it to get a job. There is no notion of disseminating knowledge just the need to establish priority and elevate oneself in the pecking order. In other words the original purpose of scientific publications has largely been lost.

I thought I’d test this by doing a (totally unscientific) poll here to see how my several readers think about this.

Nearly Time for Timed Assessments

Posted in Astrohype, Covid-19, Maynooth on May 14, 2020 by telescoper

Friday 15th May is the first day of the summer examination period at Maynooth University. I’ve written posts at the start of every examination period I’ve been involved with over the 11 years or so I’ve been blogging but this is definitely the strangest.

Owing to the restrictions imposed by the Irish Government to deal with the Covid-19 emergency, exams in the Department of Theoretical Physics this year will be unsupervised timed assessments, similar to traditional exams but done by remotely by the students and then uploaded to our virtual learning environment, Moodle. I posted about this a few weeks ago here.

The duration of these examinations is the same as usual (2 hours in most cases) and the students should be able to use past examinations to prepare reasonably well for them. The questions, however, have been set in the knowledge that students will have access to notes and textbooks so there there is a lot less ‘bookwork’ in the papers and a greater emphasis on problem solving.

Students have extra time added to scan and upload their answers and have been given detailed instructions on the entire process. Staff across the University have worked very hard to develop this new method of assessment in the short time available and to give as much instruction as possible about the technology needed.

Our overriding concern is to be as fair as possible in giving students to demonstrate what they have learnt. There are contingency plans in case things go wrong and staff will be available for consultation during the assessments in case there are problems. The intention is to ensure as much as possible that no student is penalised for circumstances beyond their control. I honestly think that we have done everything that could have been expected of us in the circumstances to make this new system work.

Nevertheless I don’t mind admitting I’m still a bit apprehensive about the forthcoming tests. A famous General once said that “no plan of battle survives first contact with the enemy*” and some improvisation may be required. Our first examination in Theoretical Physics will not be until Saturday (16th) so at least we will find out what befell Departments in the first wave tomorrow before taking our turn.

At times like this I think the best advice for examiners and examinees alike comes from Douglas Adams.

*In this context the enemy is the technology rather than the students!

Is the Expansion of the Universe Isotropic?

Posted in Astrohype, The Universe and Stuff with tags , , , , , on April 9, 2020 by telescoper

There’s a new paper out that has been making a few waves in cosmology. Here’s the title and abstract:

It’s published in Astronomy & Astrophysics but you can find it on the arXiv here.

Here’s a gratuitous pretty picture showing the distribution of the X-ray clusters used in the analysis.

The discussion in the paper focuses on two possibilities: (i) that the clusters are participating in a large-scale correlated motion; and (ii) that the Expansion of the Universe is not occurring isotropically. The latter option is the one that has attracted the most media attention (presumably because it has the most far-reaching implications). This seems to me to be a very unlikely explanation, however, because anisotropic expansion of the magnitude implied would leave a ~10% signal in the Cosmic Microwave Background which is not observed.

There is, however, a third possibility (admittedly duller than the other two) which is that there is some unknown systematic error in the observations…

Gas Filaments in the Cosmic Web

Posted in Astrohype, The Universe and Stuff with tags , , , , , on October 4, 2019 by telescoper

I saw that there’s a new paper that has just been published in the journal Science by Umehata et al with the title Gas filaments of the cosmic web located around active galaxies in a protocluster. In case you run into a paywall at Science, you may of course, find the paper on the arXiv here.

The abstract reads:

Cosmological simulations predict the Universe contains a network of intergalactic gas filaments, within which galaxies form and evolve. However, the faintness of any emission from these filaments has limited tests of this prediction. We report the detection of rest-frame ultraviolet Lyman-alpha radiation from multiple filaments extending more than one megaparsec between galaxies within the SSA 22 proto-cluster at a redshift of 3.1. Intense star formation and supermassive black-hole activity is occurring within the galaxies embedded in these structures, which are the likely sources of the elevated ionizing radiation powering the observed Lyman-alpha emission. Our observations map the gas in filamentary structures of the type thought to fuel the growth of galaxies and black holes in massive proto-clusters.

The existence of a complex cosmic web of filaments and voids has been known about for some time as it is revealed on large scales by the distribution of galaxies through redshift surveys:

You can see all my posts agged with `Cosmic Web’ here. There are also good theoretical reasons (besides numerical simulations) for believing this is what the large-scale distribution of matter should look like. Roughly speaking, dense knots of matter lie at the vertices of a three-dimensional pattern traced out by one-dimensional structures.

We have also known for some time, however, that there is more going on in cosmic structure than is revealed by light from stars in galaxies. In particular the way gas flows along the filaments into the knots plays an important role in galaxy and cluster formation. This paper reveals the distribution of gas around a giant cluster that has formed at such a node using observations made using the European Southern Observatory’s MUSE instrument.

Here’s a pretty picture:

I found out about this paper from a news piece in the Guardian with the title Scientists observe mysterious cosmic web directly for first time. That’s sufficiently misleading for me to cross-file the paper under `Astrohype’ because, as I explained above, we have been observing the cosmic web for decades. It is however only just becoming possible to observe the diffuse gas rather than having to join the dots between the galaxies so it is an exciting result. My complaint, I suppose, is that the word `directly’ is doing a lot of heavy lifting in the title!

Results from the Event Horizon Telescope

Posted in Astrohype, The Universe and Stuff with tags , , on April 10, 2019 by telescoper

Following yesterday’s little teaser, let me point out that there is a press conference taking place today (at 2pm Irish Summer Time, that’s 3pm Brussels) to announce a new result from the Event Horizon Telescope. The announcement will be streamed live here.

Sadly, I’m teaching at the time of the press conference so I won’t be able to watch, but that doesn’t mean that you shouldn’t!

I’ll post pictures and comments when I get back. Watch this space. Or you could watch this video..

UPDATE: Well, there we are. Here is the image of the `shadow’ of the event horizon around the black hole in M87:

The image is about 42 micro arcseconds across. I guess to people brought up on science fiction movies with fancy special effects the image is probably a little underwhelming, but it really is an excellent achievement to get that resolution. Above all, it’s a great example of scientific cooperation – 8 different telescopes all round the world. The sizeable European involvement received a substantial injection of funding from the European Union too!

Other parameters are here:

The accompanying EU press release is here. Further information can be found here. The six publications relating to this result can be found here:

BICEP2: Is the Signal Cosmological?

Posted in Astrohype, The Universe and Stuff with tags , , on March 28, 2019 by telescoper

An article in Physics Today just reminded me just now that I have missed the fifth anniversary of the BICEP2 announcement of `the detection of primordial gravitational waves’. I know I’m a week but I thought I’d reblog the post I wrote on March 19th 2014.You will see that I was sceptical…

..and it subsequently turned out that I was right to be so.

In the Dark

I have a short gap in my schedule today so I thought I would use it to post a short note about the BICEP2 results announced to great excitement on Monday.

There has been a great deal of coverage in the popular media about a “Spectacular Cosmic Discovery” and this is mirrored by excitement at a more technical level about the theoretical implications of the BICEP2 results. Having taken a bit of time out last night to go through the discovery paper, I think I should say that I think all this excitement is very premature. In that respect I agree with the result of my straw poll.

First of all let me make it clear that the BICEP2 experiment is absolutely superb. It was designed and built by top-class scientists and has clearly functioned brilliantly to improve its sensitivity so much that it has gone so…

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The Negative Mass Bug

Posted in Astrohype, Open Access, The Universe and Stuff with tags , , , , , on February 25, 2019 by telescoper

You may have noticed that some time ago I posted about  a paper by Jamie Farnes published in Astronomy & Astrophysics but available on the arXiv here which entails a suggestion that material with negative mass might account for dark energy and/or dark matter.

Here is the abstract of said paper:

Dark energy and dark matter constitute 95% of the observable Universe. Yet the physical nature of these two phenomena remains a mystery. Einstein suggested a long-forgotten solution: gravitationally repulsive negative masses, which drive cosmic expansion and cannot coalesce into light-emitting structures. However, contemporary cosmological results are derived upon the reasonable assumption that the Universe only contains positive masses. By reconsidering this assumption, I have constructed a toy model which suggests that both dark phenomena can be unified into a single negative mass fluid. The model is a modified ΛCDM cosmology, and indicates that continuously-created negative masses can resemble the cosmological constant and can flatten the rotation curves of galaxies. The model leads to a cyclic universe with a time-variable Hubble parameter, potentially providing compatibility with the current tension that is emerging in cosmological measurements. In the first three-dimensional N-body simulations of negative mass matter in the scientific literature, this exotic material naturally forms haloes around galaxies that extend to several galactic radii. These haloes are not cuspy. The proposed cosmological model is therefore able to predict the observed distribution of dark matter in galaxies from first principles. The model makes several testable predictions and seems to have the potential to be consistent with observational evidence from distant supernovae, the cosmic microwave background, and galaxy clusters. These findings may imply that negative masses are a real and physical aspect of our Universe, or alternatively may imply the existence of a superseding theory that in some limit can be modelled by effective negative masses. Both cases lead to the surprising conclusion that the compelling puzzle of the dark Universe may have been due to a simple sign error.

Well there’s a new paper just out on the arXiv by Hector Socas-Navarro with the abstract

A recent work by Farnes (2018) proposed an alternative cosmological model in which both dark matter and dark energy are replaced with a single fluid of negative mass. This paper presents a critical review of that model. A number of problems and discrepancies with observations are identified. For instance, the predicted shape and density of galactic dark matter halos are incorrect. Also, halos would need to be less massive than the baryonic component or they would become gravitationally unstable. Perhaps the most challenging problem in this theory is the presence of a large-scale version of the `runaway’ effect, which would result in all galaxies moving in random directions at nearly the speed of light. Other more general issues regarding negative mass in general relativity are discussed, such as the possibility of time-travel paradoxes.

Among other things there is this:

After initially struggling to reproduce the F18 results, a careful inspection of his source code revealed a subtle bug in the computation of the gravitational acceleration. Unfortunately, the simulations in F18 are seriously compromised by this coding error whose effect is that the gravitational force decreases with the inverse of the distance, instead of the distance squared.

Oh dear.

I don’t think I need go any further into this particular case, which would just rub salt into the wounds of Farnes (2018) but I will make a general comment. Peer review is the best form of quality stamp that we have but, as this case demonstrates, it is by no means flawless. The paper by Farnes (2018) was refereed and published, but is now shown to be wrong*. Just as authors can make mistakes so can referees. I know I’ve screwed up as a referee in the past so I’m not claiming to be better than anyone in saying this.

*This claim is contested: see the comment below.

I don’t think the lesson is that we should just scrap peer review, but I do think we need to be more imaginative about how it is used than just relying on one or two individuals to do it. This case shows that science eventually works, as the error was found and corrected, but that was only possible because the code used by Farnes (2018) was made available for scrutiny. This is not always what happens. I take this as a vindication of open science, and an example of why scientists should share their code and data to enable others to check the results. I’d like to see a system in which papers are not regarded as `final’ documents but things which can be continuously modified in response to independent scrutiny, but that would require a major upheaval in academic practice and is unlikely to happen any time soon.

In this case, in the time since publication there has been a large amount of hype about the Farnes (2018) paper, and it’s unlikely that any of the media who carried stories about the results therein will ever publish retractions. This episode does therefore illustrate the potentially damaging effect on public trust that the excessive thirst for publicity can have. So how do we balance open science against the likelihood that wrong results will be taken up by the media before the errors are found? I wish I knew!

Negative Mass, Phlogiston and the State of Modern Cosmology

Posted in Astrohype, The Universe and Stuff with tags , , on December 7, 2018 by telescoper

A graphical representation of something or other.

I’ve noticed a modest amount of hype – much of it gibberish – going around about a paper published in Astronomy & Astrophysics but available on the arXiv here which entails a suggestion that material with negative mass might account for dark energy and/or dark matter. Here is the abstract of the paper:

Dark energy and dark matter constitute 95% of the observable Universe. Yet the physical nature of these two phenomena remains a mystery. Einstein suggested a long-forgotten solution: gravitationally repulsive negative masses, which drive cosmic expansion and cannot coalesce into light-emitting structures. However, contemporary cosmological results are derived upon the reasonable assumption that the Universe only contains positive masses. By reconsidering this assumption, I have constructed a toy model which suggests that both dark phenomena can be unified into a single negative mass fluid. The model is a modified ΛCDM cosmology, and indicates that continuously-created negative masses can resemble the cosmological constant and can flatten the rotation curves of galaxies. The model leads to a cyclic universe with a time-variable Hubble parameter, potentially providing compatibility with the current tension that is emerging in cosmological measurements. In the first three-dimensional N-body simulations of negative mass matter in the scientific literature, this exotic material naturally forms haloes around galaxies that extend to several galactic radii. These haloes are not cuspy. The proposed cosmological model is therefore able to predict the observed distribution of dark matter in galaxies from first principles. The model makes several testable predictions and seems to have the potential to be consistent with observational evidence from distant supernovae, the cosmic microwave background, and galaxy clusters. These findings may imply that negative masses are a real and physical aspect of our Universe, or alternatively may imply the existence of a superseding theory that in some limit can be modelled by effective negative masses. Both cases lead to the surprising conclusion that the compelling puzzle of the dark Universe may have been due to a simple sign error.

For a skeptical commentary on this work, see here.

The idea of negative mass is no by no means new, of course. If you had asked a seventeenth century scientist the question “what happens when something burns?”  the chances are the answer would  have involved the word phlogiston, a name derived from the Greek  φλογιστόν, meaning “burning up”. This “fiery principle” or “element” was supposed to be present in all combustible materials and the idea was that it was released into air whenever any such stuff was ignited. The act of burning separated the phlogiston from the dephlogisticated “true” form of the material, also known as calx.

The phlogiston theory held sway until  the late 18th Century, when Antoine Lavoisier demonstrated that combustion results in an increase in weight implying an increase in mass of the material being burned. This poses a serious problem if burning also involves the loss of phlogiston unless phlogiston has negative mass. However, many serious scientists of the 18th Century, such as Georg Ernst Stahl, had already suggested that phlogiston might have negative weight or, as he put it, `levity’. Nowadays we would probably say `anti-gravity.

Eventually, Joseph Priestley discovered what actually combines with materials during combustion:  oxygen. Instead of becoming dephlogisticated, things become oxidised by fixing oxygen from air, which is why their weight increases. It’s worth mentioning, though, the name that Priestley used for oxygen was in fact “dephlogisticated air” (because it was capable of combining more extensively with phlogiston than ordinary air). He  remained a phlogistonian longer after making the discovery that should have killed the theory.

The standard cosmological model involves the hypothesis that about 75% of the energy budget of the Universe is in the form of “dark energy”. We don’t know much about what this is, except that in order to make our current understanding work out it has to act like a source of anti-gravity. It does this by violating the strong energy condition of general relativity.

Dark energy is needed to reconcile three basic measurements: (i) the brightness distant supernovae that seem to indicate the Universe is accelerating (which is where the anti-gravity comes in); (ii) the cosmic microwave background that suggests the Universe has flat spatial sections; and (iii) the direct estimates of the mass associated with galaxy clusters that accounts for about 25% of the mass needed to close the Universe.

A universe without dark energy appears not to be able to account for these three observations simultaneously within our current understanding of gravity as obtained from Einstein’s theory of general relativity.

I’ve blogged before, with some levity of my own, about how uncomfortable this dark energy makes me feel. It makes me even more uncomfortable that such an enormous  industry has grown up around it and that its existence is accepted unquestioningly by so many modern cosmologists.

Isn’t there a chance that, with the benefit of hindsight, future generations will look back on dark energy in the same way that we now see the phlogiston theory?

Or maybe, as the paper that prompted this piece might be taken to suggest, the dark energy really is something like phlogiston. At least I prefer the name to quintessence. However, I think the author has missed a trick. I think to create a properly trendy cosmological theory he should include the concept of supersymmetry, according to which there should be a Fermionic counterpart of phlogiston called the phlogistino..