Archive for Astrophysics

One Day in London

Posted in Biographical, Books, Talks and Reviews with tags , , on June 15, 2017 by telescoper

As it happens, I was in London yesterday to give an Astrophysics seminar at South Kensington Technical Imperial College. In due course I’ll post the slides as I normally do on such occasions.

It was an enjoyable day, with a train journey from Cardiff nice lunch followed by a question-and-answer session with students followed by the talk followed by a cup of tea, followed by a train ride home – all (for a change) running exactly to schedule. It was also extremely hot which meant the walk between Paddington and Imperial (across Hyde Park) left me rather sweaty. Better than getting rained on I suppose.

My hosts gave me an espresso cup, with an interesting motto on the back.


Usually when I go to Imperial or thereabouts I have a minor quandary about whether to walk or take the tube, with such factors as time, weight of baggage and weather taken into consideration before making a decision. This time, however, there was no decision to make because there were problems on the Underground in the area because of the terrible fire at Grenfell Towers, which has claimed the lives of at least 17 people (and possibly many more). The fire itself was near Latimer Road station, which is not on the line I would have taken, but there were apparently fears that the building might collapse near the line (which is overground at that point) so trains were suspended all the way from Hammersmith to Edgware Road, which disrupted the running of the Circle Line.

The venue for my talk was two or three miles away from Grenfell Towers, but in mid-afternoon you could still see smoke in the distance. It was a grim sight. I think I’ll remember yesterday afternoon very well, not because I gave a seminar, but because of the terrible events that happened earlier the same day.

There are many questions that urgently require answers. How did the fire start? Why did it spread so rapidly? Did the smoke alarms work (and if not why not)? Did the cladding on the outside of the building play a role? Did the fact that there was only a single stairwell – astonishing to my mind for a 20-storey residential building – cost lives?

I hope we’ll find the answers to these questions through a proper public inquiry. In the meantime all I can do is express my deepest condolences to those bereaved by this disaster, and wish a speedy recovery for those injured. They will need to understand what happened, urgently.

On the train home yesterday I looked at Twitter and saw this picture, of grim-faced and exhausted firefighters taking a break. I found it almost unbearably moving. We take these people for granted so much of the time, but they’re heroes – every single one of them:

A Problem of Gravity

Posted in Cute Problems with tags , , on May 9, 2017 by telescoper

Here’s a nice one for the cute problems folder.

Two spherically symmetric stars A and B of equal mass M and radius r have centres separated by a distance 6r. Ignoring any effects due to the orbital motion of the stars, determine a formula (in terms of G, M and r) for the minimum velocity with which material can be ejected from the surface of A so as to be captured by B.

Answers through the comments box please. First correct answer receives 7 points.

 

Why traditional scientific journals are redundant

Posted in Open Access, The Universe and Stuff with tags , , , , on August 20, 2015 by telescoper

Was it really six years ago that I first blogged about the Academic Journal Racket which siphons off millions from hard-pressed research budgets into the coffers of profiteering publishing houses?

Change is coming much more slowly over the last few years than I had anticipated when I wrote that piece, but at least there are signs that other disciplines are finally cottoning on to the fact that the old-style model of learned journals is way past its sell-by date. This has been common knowledge in Physics and Astronomy for some time, as I’ve explained many times on this blog. But, although most wouldn’t like to admit it, academics are really a very conservative bunch.

Question: How many academics does it take to change a lightbulb?

Answer: Change!!???

Today I came across a link to a paper on the arXiv which I should have known about before; it’s as old as my first post on this subject. It’s called Citing and Reading Behaviours in High-Energy Physics. How a Community Stopped Worrying about Journals and Learned to Love Repositories, and it basically demonstrates that in High-Energy Physics there is a massive advantage in publishing papers in open repositories, specifically the arXiv.Here is the killer plot:

citations_arXivThis contains fairly old data (up to 2009) but I strongly suspect the effect is even more marked than it was six years ago.

I’d take the argument further, in fact. I’d say that journals are completely unnecessary. I find all my research papers on the arXiv and most of my colleagues do the same. We don’t need journals yet we keep paying for them. The only thing that journals provide is peer review, but that is done free of charge by academics anyway. The profits of their labour go entirely to the publishers.

Fortunately, things will start to change in my own field of astrophysics – for which the picture is very similar to high-energy physics. All we need to do is to is dispense with the old model of a journal and replace it with a reliable and efficient reviewing system that interfaces with the arXiv. Then we’d have a genuinely useful thing. And it’s not as far off as you might think.

Watch this space.

Gay Astronomers – At Last Some Data!

Posted in Biographical, LGBT, Science Politics with tags , , , , , , on June 1, 2015 by telescoper

Some time ago I wrote a blog post entitled Where are all the LGBT Astrophysicists. I wrote that piece when I accidentally discovered that somebody had recently written a blog post (about Einstein’s Blackboard) which mentions me. I used to look after this famous relic when I was in Nottingham many years ago, you see.

There’s a sentence in that post that says

Professor Coles is one of the few out gay astrophysicists in the UK.

Well, it all depends by what you mean by “few” but at the time I wrote that  I thought there are more gay (or lesbian or bisexual or transgendered) astrophysicists out there than most people probably think. I know quite a large number personally- dozens in fact- most of whom are “out”. It’s a safe bet that there are many more who aren’t open about their sexuality too. However, it is probably the case that LGBT scientists are much less visible as such through their work than colleagues in the arts or humanities. Read two research papers, one written by a straight astrophysicist and one by an LGBT astrophysicist, and I very much doubt you could tell which is which. Read two pieces of literary criticism, however, and it’s much more likely you could determine the sexual orientation of the writer.

You might ask why it matters if an astrophysicist or astronomer is straight or gay? Surely what is important is whether they are good at their job? I agree with that, actually. When it comes to career development, sexual orientation should be as irrelevant as race or gender. The problem is that the lack of visibility of LGBT scientists – and this doesn’t just apply to astrophysics, but across all science disciplines – could deter young people from choosing science as a career in the first place.

Anyway, at last we have some evidence as to whether this might be the case. In 2014 the Royal Astronomical Society (of which I am a Fellow) carried out a demographic survey of its membership. This happens from time to time but this one was the first to include a question about sexual orientation. The Institute of Physics did a similar survey about Physics about a decade ago, but did not include sexual orientation among its question, so this is the first time I’ve seen any data about this from a systematic survey. The results are quite interesting. About 7% of UK respondents (from a total of around a thousand) refused to answer the sexual orientation question but, among those who did, 3% identified themselves as bisexual and 4% as gay men. Both these proportions are significantly higher than the figures for the general UK population reported by the Office of National Statistics. The fraction of respondents in the RAS Survey declaring themselves to be heterosexual was 84%, whereas the corresponding figure from the ONS Survey was 93.5%. The number of UK respondents in the RAS Survey identifying as lesbian was only 0.2%; the proportion of respondents identifying themselves as male was 77.5% versus 21.3% female, which accounts for only some of the difference between gay and lesbian proportions.

So, according to the survey, gay men are actually significantly over-represented in the Royal Astronomical Society compared to the general population. That confirms the statement I made earlier that there are more gay astronomers than you probably think.  It also shows that there is no evidence that gay men are deterred from becoming astronomers. In fact, it seems to be quite the opposite. It’s a different story when it comes to other demographics, however. The RAS membership is older, less ethnically diverse, and more male-dominated than the the general population, so there’s a lot of work to be done redressing the balance there.

On the other hand, next time the Royal Astronomical Society is looking to elect a President it will naturally want to find someone who is representative of its membership, which means an ageing white gay male. I rest my case.

 

Do-It-Yourself Supernova Explosion

Posted in Education, The Universe and Stuff with tags , , , , on August 15, 2014 by telescoper

Visitors to the office of the Head of the School of Mathematical and Physical Sciences at the University of Sussex often remark upon the presence of these two objects and inquire as to their purpose:

Supernova

Since I don’t play golf and am a bit long in the tooth to be a fan of Peppa Pig, most assume that it must be for some strange astrophysical reason. I tried asking on Twitter what people think I use them for, and the most common answer was to demonstrate the relative size of the Earth and Moon. As Roy Walker would have said, “That’s a good answer, but it’s wrong”.

In fact I use the objects concerned to demonstrate what goes on when a star goes supernova.

The point is that a supernova explosion begins with gravitational collapse of the progenitor star, so why does that manifest itself as an explosion? The point is that the outer layers are blown off while the core collapses into a compact object such as a neutron star or, perhaps, a black hole.

The way to demonstrate this is first to balance the golf ball (representing the outer layers) on top of the beach ball; the air hole in the latter is a useful place to do this. You then lift the conjoined objects to a reasonable height and drop them onto the table or bench provided for such a purpose in a lecture theatre. The objects fall together under gravity until the beach ball hits the surface. You will find that the beach ball (representing the core) stops still while the golf ball (representing the outer shells) shoots upwards as most of the kinetic energy of the system is transferred to it during the bounce.

I think this is quite an effective demonstration, but I’d encourage inexperienced lecturers to note that there is a Health and Safety Issue, so it is necessary to carry out a risk assessment before attempting it. When I first did this during a lecture many years ago, I used a ball bearing rather than a golf ball and a fully-inflated and much larger beach ball instead of the more manageable (and slightly deflated) Peppa Pig one I now use. I told the students in the audience to watch carefully what happened and then dropped them as described above…

What happened in that case was that the ball bearing rocketed up so fast that it reached the ceiling and smashed into the lights above the lecturer’s bench, whereupon there was a very loud bang and I was showered with broken glass and other debris. I have to say that got the loudest round of applause I’ve ever had while lecturing, but it wasn’t exactly the effect I’d been hoping for.

But the real reason for posting today is to wish a very happy 65th birthday to supernova expert extraordinaire and occasional reader of this blog, Robert Kirshner of Harvard University, who has celebrating along with a number of my astro-chums at a conference in Australia.

Many happy returns, Bob!

Fly through of the GAMA Galaxy Catalogue

Posted in The Universe and Stuff with tags , , , , , , , , on March 13, 2014 by telescoper

When I’m struggling to find time to do a proper blog post I’m always grateful that I work in cosmology because nearly every day there’s something interest to post. I’m indebted to Andy Lawrence for bring the following wonderful video to my attention. It comes from the Galaxy And Mass Assembly Survey (or GAMA Survey for short), a spectroscopic survey of around 300,000 galaxies in a region of the sky comprising about 300 square degrees;  the measured redshifts of the galaxies enable their three-dimensional positions to be plotted. The video shows the shape of the survey volume before showing what the distribution of galaxies in space looks like as you fly through. Note that the galaxy distances are to scale, but the image of each galaxy is magnified to make it easier to see; the real Universe is quite a lot emptier than this in that the separation between galaxies is larger relative to their size.

The faces of highly followed astronomers on Twitter

Posted in The Universe and Stuff with tags , on February 28, 2014 by telescoper

On Twitter? Looking for an astronomer or astrophysicist to follow? Here’s a Rogues Gallery…