Showing posts from November, 2011


I've been interested in chaos since reading Gleick's book back in the 1980s. I was first introduced to fractals when I was a summer student at the Rutherford Labs in the late 1980s; this was when colour printers were rare and expensive and I spent a lot of time convincing the guardian of the printer that printing out large colour fractals for my bedroom wall was essential for my studies of proton-anti-proton scattering.

But that's another story.

A little while ago, I caught an excellent documentary called "The Secret Life of Chaos" by the equally excellent presenter, Jim Al-Khalili. This linked a lot of topics, including chaos and complex systems, which is when a group of things following simple rules results in complicated (and sometimes difficult to predict) behaviour.

One of the key things I learnt was the importance of this man
in some of the earliest work in the field. I'm sure a number of you recognise him as Alan Turing. I first came across him in his …

The Star Formation History and Dust Content in the Far Outer Disc of M31

You wait for a bus, and then two come along at once.

Postdoctoral researcher, Edouard J. Bernard, working with Annette Ferguson at Edinburgh's Institute for Astronomy, and myself, has had his paper on the star formation history in a couple of fields observed with the Hubble Space Telescope. Before continuing, I want to say that the IfA has the best, thickest custard in the entire world!

The focus of the paper is deep Hubble Space Telescope fields in the outer parts of the Andromeda galaxy. The absolutely wonderful thing about Hubble is that being above the atmosphere, we can accurately measure the brightness of faint stars, but the annoying thing about Hubble is that the field o view is tiny. Here's the fields we got
The grey area is the sky that we've observed as part of the PAndAS program with Canada-France-Hawaii Telescope, whereas the tiny squares are the bit covered by Hubble; all telescope time is quite competitive, but getting lots of Hubble time is difficult (altho…

Conservation Laws

With exam marking and committee meetings, it has been a slow week, but here's a pop quiz.

What does this woman
have to do with this video?
(the video has a nasty crack at the end of it, and so don't watch if squeamish). The answer is not that the woman in the photograph is the girl in the video.

Of course, what we are looking at here is a collision, and due to the use of the yoga balls, it is a pretty elastic collision, and so energy is almost conserved (and if you account for the energy that goes into heat and noise, it's completely conserved).

But what we all remember from our high school physics is that the thing called momentum, the sum of mass times velocity, is always conserved in collisions, and so if, before the collision, we take the mass of the boy and multiply it by his velocity, and then do the same for the girl, and then add the two quantities together, this sum is the total momentum. If we do the same after the collision (assuming no external forces), the tot…

Black hole noms: planetary treats for the galactic monster

I didn't write the title, and had to check the dictionary on what a nom is (and was surprised that it was actually a word), but I wrote a brief article for The Conversation

It summarizes a paper by Kastytis Zubovas of the University of Leicester on the continual burps of energy from the black hole at the centre of the Milky Way. You can read the original paper here

Sgr A* flares: tidal disruption of asteroids and planets?

Kastytis Zubovas, Sergei Nayakshin, Sera Markoff
(Submitted on 31 Oct 2011) It is theoretically expected that a supermassive black hole (SMBH) in the centre of a typical nearby galaxy disrupts a Solar-type star every ~ 10^5 years, resulting in a bright flare lasting for months. Sgr A*, the resident SMBH of the Milky Way, produces (by comparison) tiny flares that last only hours but occur daily. Here we explore the possibility that these flares could be produced by disruption of smaller bodies - asteroids. We show that asteroids passing within an AU of Sgr A* co…