Interview with Dr Julian Onions

On the 31st of August 2019, I interviewed Dr Julian Onions. Julian has always had an interest in astronomy over many years but
decided to take it further by studying for a doctorate in astrophysics
at Nottingham University.  There he studies computer models of galaxy
formation using some of the biggest computers in the world and builds
model universes using mostly dark matter. He is also a keen amateur
taking photographs of various astronomical objects but is brought back
to earth by his department colleagues who get to use some of the biggest
telescopes yet built with tracking to die for. Click on the button to start the interview.


It has come to my attention that listeners on mobile devices can not play the audio so I decided to write it out.

Theodore: What first interested you into astronomy/cosmology?

Dr Julian Onions: I’ve always liked looking at the stars and so on. I think early on it was Patrick Moore on the Sky at Night that got me interested, but what really got me interested was taking an Open Univerity course on the structure of stars. Suddenly I had this lightbulb moment where, wow, we can actually understand whats going on in stars without being able to visit or touch using physics and it just blew me away! I wanted to know more.

T: What would be your advice for young astronomers?

J: Young astronomers, well I think they come in two categories; The amateur astronomer where you are looking at stars and really understanding the night sky, you know constellations and you know where stars are and so on. And that’s just a matter of working it out and understanding it. If you want to become a professional astronomer then you have to go down the exam routes, so GCSE’s and A-Levels in maths and physics and to like that sort of thing. It’s all maths and physics, and quite a lot of computing nowadays too. And to have a passion for the subject because there are quite a few bits which are really quite hard. The passion has to carry you over the bits you don’t really like.

T: What code do you use for simulations of galaxy formation

J: Well people use all sorts, originally a lot of it was done using 4-tran which I thought had died out back in the 1990s but people still use that. A lot of stuff now is done in C or C++. That’s used for more heavy simulations so we can run it as fast as possible. Having done that you typically end up with large amounts of data what you then analyse. That’s usually done in more modern languages like python, pearl a specialist one is R. That’s a lot easier to cope with and less high pressure

T: How big are these simulations in bytes

J: Bytes, they’re not that big. In source code, they’re probably about 20 or 30 files each possibly 1,000 lines long all doing different things. So one might be working on gravity, one might be working on light and so on and people tend to dabble with those. For instance, one simulation might be looking at how often stars explode in supernovas and say well the last one we didn’t get enough supernovas so we’re going to twiddle with this code and this one. Typically running it, it usually runs on massive computers. So I’ve run one on a computer with 100,000 CPU’s on it. I only used 64,000 of them but it was running 64,000 copies of the program at once. Each one is looking after a tiny bit of the universe and telling each other, I’ve done this bit, this is what I found, what have you found and we’ll talk about it. Now we know what the universe is like we’ll go on and do another 1,000 years and so on. Typically that is the hard bit, getting them not argue and keep the communication flowing because otherwise, it ends up with everyone shouting at everyone else and no one getting on with the work.

T: Thanks for talking to me

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