Dark matter and cosmology

Overview

Recent results from the Bullet Cluster suggest that dark matter is most likely some new particle of nature rather than modified gravity, but exactly what it is remains a mystery. If it is a new particle, then billions of these will flow through your head by the time you finish reading this webpage (without effect thankfully). This is such a striking thought that it has already inspired many artists and writers, from Cornelia Parker's famous Cold Dark Matter sculpture to Philip Pullman's His Dark Materials.

One of the key science goals of our group is to answer the question: "What is dark matter?" Our approach is to construct actual images of the dark matter distribution in the Universe by measuring its gravitational influence. Comparing these images with state of the art numerical simulations (that assume something about the nature of dark matter), we can then rule out dark matter candidates, honing in on what dark matter actually is. So far, it seems that dark matter is a very cold "collisionless" fluid - perfectly consistent with a new particle that lies beyond the standard model of particle physics. But there is still plenty of room for other more exotic theories that rely on new physics like extra spatial dimensions.

All in all, it is a very exciting time for the field. In the next five years, our theoretical models will become significantly more accurate as computers increase in power. The Gaia satellite - due to launch this year - will measure the positions and velocities of a billion stars in our Galaxy, allowing us to accurately measure the dark matter distribution through the Milky Way for the first time. And there is a very real prospect that we will detect a dark matter particle - either in experiments deep underground, or by creating some at the Large Hadron Collider in CERN. 

On this last point, it is interesting to make comparisons with another elusive particle - the neutrino. First invented by Wolfgang Pauli in the 1930's to explain missing mass and momentum in radioactive beta decay, Pauli said of the particle: "I have done a terrible thing, I have postulated a particle that cannot be detected." Some thirty years later, Reines and Cowan proved Pauli wrong by detecting neutrinos coming from a nearby nuclear reactor. Today, we have entered the realm of neutrino astronomy, using them as a new window onto the cosmos. Perhaps nature will be kind and allow us to do the same with dark matter in the near future.

Dark matter is vital to cosmology, being one of the main constituents of the Universe. We use supernovae to probe the structure of the Universe by measuring its expansion rate. We are part of the upcoming surveys 4MOST TiDES and Euclid. 

The Time-Domain Extragalactic Survey (TiDES) will conduct spectroscopic follow up of optical transients observed by upcoming sky surveys such as the Large Synoptic Survey Telescope (LSST). Over TiDES proposed observing timeline, it will observe spectra of over 30,000 supernovae, of which about 25,000 will be type-Ia supernovae. This will be the largest spectroscopic sample of SNe Ia to date and will allow us to further investigate the properties of sub-types of type-Ia supernovae and their systematic effects in the use for constraining the cosmological model and dark energy.

Due to the large number of spectra that will be observed, we are at a stage where visually analysing data is impractical. Therefore, we are currently developing a pipeline for TiDES that will automate the spectroscopic analysis of the observed supernovae spectra. In the future, we hope to the use the results from the spectral analysis to investigate the systematics present in using type-Ia supernovae for constraining the cosmological model and dark matter.

For further information about our latest research and results, please see the pages of Profs. Justin Read and Bob Nichol.