Research Fellows Directory
Professor Mark Sullivan
University of Southampton
"What is the Universe made of?" - a question that has fired imagination for thousands of years. Perhaps surprisingly, the nature of over two thirds of the Universe is a mystery to us. We know that the Universe is getting bigger. We also know that gravity from the matter it contains, such as planets and stars, should pull everything together to slow down this expansion. But what we observe is very different. Experiments in the last decade have shown that, astonishingly, our Universe is expanding at an ever faster speed, opposite to the effect expected from 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. My research tests these theories using cosmic explosions known as supernovae, violent thermonuclear explosions from dying stars that outshine entire galaxies. These supernovae always explode with about the same brightness, "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.
Though my research 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.
Interests and expertise (Subject groups)