Physics and Cosmology with Supernovae

The quest to understand what the universe is made of has fired our imagination for thousands of years. Finding the answer has inspired the creativity of generations of scientists, so it may come as a surprise that the nature of over 90% of the Universe is a mystery to us. We know that most of the matter in the Universe is invisible to us, in an unknown form called "dark matter". We also know that the Universe is getting bigger, an expansion driven by a "Big Bang" nearly 14 billion years ago. As the Universe contains objects like stars and planets as well as the unseen dark matter, gravity pulling everything together should slow down this expansion. However, experiments in the last 15 years have come to a quite different conclusion: Our Universe is expanding at an ever faster speed -- the opposite to the effect of gravity.

This presents one of the most exciting challenges to modern science: the quest to understand this unexpected acceleration. The unknown substance responsible is called "dark energy"; as the name suggests we know little about it. We think that it makes up about 70% of the Universe with an incredibly low density -- much less than a speck of dust in a volume of space the size of the Earth. Beyond that, there are only theories; perhaps most shockingly, some believe that Einstein's theory of general relativity, the bedrock of modern cosmology, simply doesn't work on the largest scales.

This project lays the foundation to test these theories using cosmic explosions known as supernovae, violent thermonuclear explosions from dying stars that can outshine entire galaxies. These supernovae always explode with about the same brightness, and are "standard candles" or cosmic rulers which can measure vast intergalactic distances. I hunt out these supernovae billions of light-years away, and measure their brightness as they appear to us on Earth. When combined with a knowledge of their intrinsic brightness we can infer their distance, and, from that, information about the mysterious dark energy.

Recent research has unexpectedly thrown up a extraordinary variety of new types of these supernova explosions. New surveys, charting huge areas of the sky on unprecedented short time-scales, are finding cosmic explosions for which we have no explanation -- from ultra-luminous supernova explosions seen almost to the edge of the universe, to faint blips that barely register on our detectors. Not only is understanding dark energy a challenge, but these new explosion types suggest that the tools that we use for its study may also be poorly understood. This project will investigate the physics of the standard candles that we take for granted.

Though this project has limited practical application, there are fewer more fundamental questions about Nature that remain to be answered than the question of dark energy. Understanding the Universe we live in has challenged us ever since early humans became fascinated by the environment around them. Research such as this continues our exploration and understanding of the Universe that surrounds and intrigues us.

The Southampton Astronomy Group has achieved significant impact in both its outreach activities and in knowledge exchange, and this new project will consolidate and broaden the variety of this impact. The School's outreach work reaches a large number of people (typically 9000 per year), in which astronomy plays a central role. While these activities have traditionally focussed on the general public and students, more recently there have been targetted opportunities to give support to teachers, such as the School's partnership with the local Science Learning Centre. Thus we have been able to provide input and support to the teachers which can have much longer-term value for their future teaching of basic scientific principles. Our outreach activities, including teacher support, is enhanced through the new Winchester Science Centre and Planetarium, in which the Astronomy Group plays a significant role. There have also been many opportunities for Astronomy Group members to participate in science open days, fairs and cafes, interest in which has exploded following the highly successful International Year of Astronomy in 2009.

Exploiting astronomy research in completely different environments and communities has always been important in the Astronomy Group whenever appropriate circumstances arise, and our work has recently provided two examples of such knowledge exchange. Both were related to the mathematical techniques that had to be developed in order to model the rapid variability observed in X-ray binaries and AGN. The techniques themselves were of interest to the University's own Complexity Group, whilst the students involved in developing the techniques for their theses obtained positions in the financial world where these techniques have the potential to be applied to the variability of stocks and shares. Furthermore, the Astronomy Group's years of developing satellite hardware led to the creation of Symetrica, a now highly successful spin-off company in the international security market, who have in turn funded PhD studentships and participate in supporting our undergraduate projects.