Queen's University Belfast Astronomy Observation and Theory Consolidated Grant 2017-2020

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Supernovae create the heavy chemical elements we see in our solar system, the Galaxy and entire visible Universe. While stars evolve over millions or billions of years, a supernova explosion happens in seconds and the glowing remnant lasts for years. We aim to understand how these explosions happen and how they create the neutron stars, pulsars and black holes in our galaxy. The cores of massive stars collapse at the end of their nuclear burning life and the gravitational potential energy released drives an explosion through the interaction of neutrinos with the dense inner region of the star. How the most massive stars explode, and if a black hole is formed, is uncertain and there is a huge diversity in the energy observed in the known supernova population. Our proposed work will address these questions along with trying to find the sources that may create gravitational waves in the Universe. The most likely sources are merging neutron stars or black holes and it is expected that gravitational waves will finally be found. The question will then turn to finding the sources. The thermonuclear supernovae that are used as cosmic yardsticks and led to the Nobel Prize winning discovery of dark energy come from white dwarf stars. But how they explode and what the progenitor systems are still eludes us. Competing models of two merging white dwarfs, or single white dwarfs with a normal stellar companion are still feasible. Most likely there are several ways to explode a white dwarf - a star greater than the mass of the sun, but the size of the earth. We are in an excellent position to make advances in these areas with our theoretical computer codes and world leading sky survey data. The elements created in supernovae form planetary systems in our galaxy - iron, silicon, oxygen, magnesium are all critical to forming planetary systems. The diversity in the known planetary systems around other stars in our galaxy (called exoplanets) is astounding. We know of thousands of exoplanets, with massive hot jupiters, multiple planetary systems and super-earths now commonly found. We can see planet formation in the disks of young stars during their first few million years of life. The latest large facility built in the southern hemisphere (ALMA), has provided spectacular data on proto-planetary disks and our work on the chemistry of the disk aims to understand their origins. Our work will probe the atmospheres of these distant worlds by carefully extracting the light that passes from the parent star through the atmosphere of the planet. We can also measure the ages of stars to set constraints on how planetary systems evolve with time and what the constraints for life bearing planets may be. The top priority in this area is to find another earth like planet - the right size, age and distance from its parent star to support an atmosphere and liquid water. This search requires careful consideration and tests of the methods to extract the tiny signals we expect and we propose to develop this with an eye on the future prize of detecting an earth twin. A critical part of astrophysics is pulling together our detailed knowledge of physics that we can measure on earth to what we can only see (through electromagnetic radiation) in the distant Universe. This will be done through computer calculations of model atoms. These codes calculate how electrons are excited in atoms and ensures that astrophysics codes identify the elements that cause the spectral lines and features we see in supernovae, supermassive black holes, galaxy spectra and stars. Finally, we propose to run a novel experiment to use the UK's most powerful laser (the VULCAN facility) to mimic the physics of gas at the centre of a galaxy. The laser can produce a large enough x-ray flux that the conditions are equivalent and we, for the first time, can test the world's leading computer code that is used to model the central regions of galaxies close to their black holes.