Dark Matter from the Sun?

Posted in The Universe and Stuff with tags , , , , , , , on October 16, 2014 by telescoper

This afternoon while I was struggling to pay attention during one of the presentations at the conference I’m at, when I noticed a potentially interesting story going around on Twitter. A little bit of research revealed that it relates to a paper on the arXiv, with the title Potential solar axion signatures in X-ray observations with the XMM-Newton observatory by Fraser et al. The first author of this paper was George Fraser of the University of Leicester who died the day after it was submitted to Monthly Notices of the Royal Astronomical Society. The paper has now been accepted and the final version has appeared on the arXiv in advance of its publication on Monday. The Guardian has already run a story on it.

This is the abstract:

The soft X-ray flux produced by solar axions in the Earth’s magnetic field is evaluated in the context of ESA’s XMM-Newton observatory. Recent calculations of the scattering of axion-conversion X-rays suggest that the sunward magnetosphere could be an observable source of 0.2-10 keV photons. For XMM-Newton, any conversion X-ray intensity will be seasonally modulated by virtue of the changing visibility of the sunward magnetic field region. A simple model of the geomagnetic field is combined with the ephemeris of XMM-Newton to predict the seasonal variation of the conversion X-ray intensity. This model is compared with stacked XMM-Newton blank sky datasets from which point sources have been systematically removed. Remarkably, a seasonally varying X-ray background signal is observed. The EPIC count rates are in the ratio of their X-ray grasps, indicating a non-instrumental, external photon origin, with significances of 11(pn), 4(MOS1) and 5(MOS2) sigma. After examining the constituent observations spatially, temporally and in terms of the cosmic X-ray background, we conclude that this variable signal is consistent with the conversion of solar axions in the Earth’s magnetic field. The spectrum is consistent with a solar axion spectrum dominated by bremsstrahlung- and Compton-like processes, i.e. axion-electron coupling dominates over axion-photon coupling and the peak of the axion spectrum is below 1 keV. A value of 2.2e-22 /GeV is derived for the product of the axion-photon and axion-electron coupling constants, for an axion mass in the micro-eV range. Comparisons with limits derived from white dwarf cooling may not be applicable, as these refer to axions in the 0.01 eV range. Preliminary results are given of a search for axion-conversion X-ray lines, in particular the predicted features due to silicon, sulphur and iron in the solar core, and the 14.4 keV transition line from 57Fe.

The paper concerns a hypothetical particle called the axion and I see someone has already edited the Wikipedia page to mention this new result. The idea of the axion has been around since the 1970s, when its existence was posited to solve a problem with quantum chromodynamics, but it was later realised that if it had a mass in the correct range it could be a candidate for the (cold) dark matter implied to exist by cosmological observations. Unlike many other candidates for cold dark matter, which experience only weak interactions, the axion feels the electromagnetic interaction, despite not carrying an electromagnetic charge. In particular, in a magnetic field the axion can convert into photons, leading to a number of ways of detecting the particle experimentally, none so far successful. If they exist, axions are also expected to be produced in the core of the Sun.

This particular study involved looking at 14 years of X-ray observations in which there appears to be an unexpected seasonal modulation in the observed X-ray flux which could be consistent with the conversion of axions produced by the Sun into X-ray photons as they pass through the Earth’s magnetic field. Here is a graphic I stole from the Guardian story:

axions

Conversion of axions into X-rays in the Earth’s magnetic field. Image Credit: University of Leicester

I haven’t had time to do more than just skim the paper so I can’t comment in detail; it’s 67 pages long. Obviously it’s potentially extremely exciting but the evidence that the signal is produced by axions is circumstantial and one would have to eliminate other possible causes of cyclical variation to be sure. The possibilities that spring first to mind as an alternatives to the axion hypothesis relate to the complex interaction between the solar wind and Earth’s magnetosphere. However, if the signal is produced by axions there should be characteristic features in the spectrum of the X-rays produced that would appear be very difficult to mimic. The axion hypothesis is therefore eminently testable, at least in principle, but current statistics don’t allow these tests to be performed. It’s tantalising, but if you want to ask me where I’d put my money I’m afraid I’d probably go for messy local plasma physics rather than anything more fundamental.

It seems to me that this is in some sense a similar situation to that of BICEP2: a potentially exciting discovery, which looks plausible, but with alternative (and more mundane) explanations not yet definitively ruled out. The difference is of course that this “discovery paper” has been refereed in the normal way, rather than being announced at a press-conference before being subjected to peer review…

Choose My Mugshot

Posted in Beards, Biographical on October 15, 2014 by telescoper

For some time now staff and students of the School of Mathematical & Physical Sciences at the University of Sussex have complained that the picture of me on my office door is of a non-bearded person. Recently therefore I made a visit to a professional photographer so he could take a picture of the hirsute me and tried his best to make me look presentable in the process. I am now told I have to pick one of the following three shortlisted photographic representations. They all suffer from the problem that they look like me, so I have no idea what to pick. I thought I’d have a bit of a laugh and see if I can crowd-source a favourite.

Here are the contenders:

 

Please vote here

Physicists and astronomers followed by physicists and astronomers on Twitter

Posted in Uncategorized on October 15, 2014 by telescoper

telescoper:

For those of you interested in this sort of thing, this is the sort of thing you will find interesting…

Originally posted on Lucretius, ver. 21c:

This page is a one-time snapshot based on data collected 2014-Oct-10.

The list below covers physicists and astronomers who have over 1,000 Twitter followers. For each user, it indicates (1) the number of list members who follow the user and (2) the total number of followers of the user.

See Physicists on Twitter and Astronomers on Twitter for the full-format and periodically updated lists of highly followed physicists and astronomers.

User Followers who are highly
followed physicists & astronomers
(listed here and here )
Followers
seanmcarroll 119 34053
BadAstronomer 115 327107
neiltyson 114 2492209
ProfBrianCox 106 1456963
AstroKatie 105 15106
elakdawalla 84 46224
plutokiller 82 18869
chrislintott 81 13909
sarahkendrew 80 3094
jonmbutterworth 78 10285
CatherineQ 74 13818
cosmicpinot 74 9694
astropixie 72 4619
starstryder 66 18523
lirarandall 65 12099
sc_k 65 5943
dalcantonJD 65 1807
astroengine 64 17253
skyponderer 63 4948
FrankWilczek 63 3773
NoisyAstronomer 62 8058
DrMRFrancis 62

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Autumn Song

Posted in Poetry with tags on October 14, 2014 by telescoper

Know’st thou not at the fall of the leaf
How the heart feels a languid grief
         Laid on it for a covering,
         And how sleep seems a goodly thing
In Autumn at the fall of the leaf?

And how the swift beat of the brain
Falters because it is in vain,
         In Autumn at the fall of the leaf
         Knowest thou not? and how the chief
Of joys seems—not to suffer pain?

Know’st thou not at the fall of the leaf
How the soul feels like a dried sheaf
         Bound up at length for harvesting,
         And how death seems a comely thing
In Autumn at the fall of the leaf?

by Dante Gabriel Rossetti (1828-1882)

More of L’Aquila

Posted in Uncategorized with tags , , on October 12, 2014 by telescoper

At the risk of boring you all with even more pictures of L’Aquila, here are a few more pictures I took with my phone while out and about over the past week.

First, here’s the Gran Sasso Science Institute (GSSI) where our workshop is being held:

IMG-20141010-00423

The following sites can all be found within a few minutes’ walk of the GSSI (which is itself just a few minutes from my hotel). In particular there is the historically important Romanesque church of Santa Maria di Collemaggio which dates back to the 13th Century. The façade looks in good nick, although there is evidence of recent repair. However, the back of the church collapsed completely during the 2009 Earthquake and is currently being rebuilt. There is also cracking and significant bowing of the wall on the left hand side, hence the supporting structures.

Roy Keane shaves beard but will still compete for Beard of Autumn

Posted in Beards with tags , , on October 12, 2014 by telescoper

telescoper:

I felt the urge to reblog this to encourage folks to vote in the Beard of Autumn poll, despite not having been nominated myself, especially since the great Leonard Cohen is a candidate. Surely he deserves to win more than Roy Keane who has already shaved off his beard?

Originally posted on Kmflett's Blog:

Beard Liberation Front

Press Release 10th October Contact Keith Flett 07803 167266

Roy Keane shaves beard but will still compete for Beard of Autumn

The Beard Liberation Front, the informal network of beard wearers, has said that it regrets but respects the decision of Roy Keane to shave his beard ahead of Ireland’s European Championship game against Gibraltar on Saturday.

Keane has a history of suddenly shaving his beard but the campaigners say that the four seasonal awards run each year are designed to capture in particular those who have noteworthy but transient beards.

The BLF has for that reason decided to keep Keane on the longlist for Beard of Autumn, the winner of which is announced on October 24th after a public on-line poll

The Award is the final one of four seasonal Awards before the announcement of the coveted Beard of the Year Award at…

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Excursion to Sulmona

Posted in Uncategorized with tags , , on October 11, 2014 by telescoper

I’m here on my own over the weekend so I decided to make the most of the lovely weather (it was a sunny 28° C today) and take a small excursion by train. The railway station at L’Aquila is situated on a branch line so the options from here are limited: up or down. I decided to take the “up” line to the town of Sulmona, which is 61km away by train. The ticket cost a mere €4.80 and though the train was a bit old, it was right on time in both directions. The journey time of an hour each way might seem a bit long, but the journey is through rather mountainous terrain and the service is a slow Regionale stopping service so I didn’t expect it to be a quick journey. On arrival I discovered that the Stazione Centrale is in fact pretty far from central but it was a pleasant walk of about half an hour into the small city centre.

Sulmona is famous for two things. One is that it is the birthplace of the poet Ovid who is  remembered by a fine bronze statue in the Piazza XX Settembre. The other famous thing is the Confetti di Sulmona, sugar-coated almonds coloured in such a way to look like oversized Smarties and presented in various disguises, e.g. as flower petals.

The town itself was almost totally destroyed by an earthquake in 1706. That’s a bit of a theme around these parts. You might think people would get fed up living in a place where natural catastrophes happen so regularly, but apparently not. Anyway, quite aside from the fact that many of the buildings are clearly of late eighteenth or early nineteenth century, which is not the case in L’Aquila, the reconstruction of Sulmona has made it a much airier place: the squares are larger and more open, and the streets wider. While the topography around L’Aquila is complex – the town itself sits on a hill surrounded by numerous local maxima, minima and saddle-points –  Sulmona sits in a broad flat plain on which the first and second derivatives behave in a much more sensible fashion.  I have to say that I have found L’Aquila quite oppressive at times during this visit. I don’t believe in ghosts of course, but there is so much evidence of destruction all around that it definitely has something of a haunted atmosphere. It was good to get away to a town whose wounds have healed.

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