As astronomers, our job is to make sense of the Universe around us:
what it was like at the beginning, how it came to look the way it
does at the present day, and (potentially) what its fate could be in the
future. Unfortunately, the vast majority of what the Universe is made of
- namely, dark matter and dark energy - cannot be detected by us via
To get around this issue, numerical simulations of cosmological structure
formation have become one of the key tools used by astronomers to try and
understand the Universe. In short, these simulations allow us to create
artificial universes on our desktop computers to then compare to the real
thing. Some of the topics I have recently been involved in are described
The first structures in a Cold Dark Matter Universe
Understanding the present day structure and distribution of cold dark matter
(CDM) haloes is key to dark matter detection experiments. Using the present
generation of N-body codes we can, for the first time, simulate the entire
CDM mass function: from the largest clusters, all the way down to the scale
of Earth-mass haloes. Establishing the CDM concentration-mass relation and
its phase-space distribution over 22 orders of magnitude is a computationally
challenging, but (hopefully!) fruitful endeavour. (Image: A 100 solar mass CDM
halo at z=0.)
Sterile neutrinos as dark matter
While CDM is the leading candidate for the dark matter, there are other well-motivated
particle physics models that could be viable alternatives. One such example is a sterile
neutrino, which behaves as warm dark matter, and exhibits structure formation that is
manifestly different to CDM. Using hydrodynamical simulations like EAGLE or semi-analytic
models like GALFORM, we can study galaxy formation in sterile neutrino cosmologies and
look for observables that could be used to distinguish it from CDM.
(Image: the formation of a warm dark matter halo.)
Large-scale structure and modified gravity
The wealth of cosmological data that will be available
from the upcoming generation of surveys could prove key
to understanding the accelerated expansion of the Universe. Using the HOD model
to create mock galaxy catalogues, we can use the statistics of clustering
to distinguish GR from more exotic models of gravity. Weak gravitational
lensing is another important tool at our disposal for this purpose.
(Image: The Integrated Sachs-Wolfe effect in a cosmological simulation,
calculated using RAY-RAMSES, an on-the-fly ray tracing algorithm.)
Lumiere, which is the UK's largest light festival, was attended by around 200,000 visitors
over the course of four days. Our involvement at the ICC was to create "The World Machine"
- the story of the birth of modern cosmology told through a movie projected on Durham Cathedral.
You can see the full show in the video below.
The Summer Science Exhibition, which is held annually the Royal Society in London attracts
over 10,000 members of public in a week-long celebration of science. The ICC's exhibit,
titled "Galaxy Makers" gave visitors a chance to build their own galaxy (or universe!)
using different quantities of "dark matter", old and young stars, and even black holes.
There was also the opportunity to fly-through the simulated EAGLE universe using
an Oculus Rift, which proved to be one of the most popular attractions for visitors.
A 2D version of the fly-through can be seen in the video below. You can also have a go
at building your own personal galaxy or universe at the
Galaxy Makers website!