Queen's University Belfast Astronomy Observation and Theory Consolidated Grant 2020-2023

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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. In 2017 a breakthrough discovery was made when the first electromagnetic counterpart to a gravitational wave source was found. This was termed a kilonova because it was 1000 times brighter than a nova. The gravitational waves and the kilonova were from a pair of merging neutron stars. The optical and infrared light arose from the radioactive decay of heavy elements, which we call r-process elements. These are heavier than iron in the periodic table and such neutron star mergers may be responsible for all these heavy elements. Or projects will find more of these in the coming years and the combination of gravitational waves and electromagnetic signals opens up a new window on the Universe. 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 exactly how they explode and what the progenitor systems are still eludes us. A white dwarf is a star greater than the mass of the sun, but the size of the earth. They are incredibly dense, one teaspoon of WD material weighs about 10 thousand tonnes. To understand how they explode, we will model their spectra with the most sophisticated 3 dimensional computer models that currently exist. 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. Hot Jupiters, multiple planetary systems and super-earths are now commonly found in surveys to discover new planets. 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 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 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. We will soon have extraordinarily precise spectrometers on the biggest telescopes to measure the velocity of stars down to metres per second. At this level, it is no longer the instrument measuring precision that hinders our planet searching, but the real activity on the surface of Sun like stars. Our project will aim to understand and mitigate this effect. 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 astrophysical models identify the elements that cause the spectral lines in supernovae, supermassive black holes, galaxy spectra and stars. Now that we have detected a kilonova we must do the same calculations for the heaviest elements. We will also run novel experiments to use powerful lasers (e.g. the VULCAN laser) to mimic the physics of gas that causes x-ray emission in accreting sources such as black hole binaries. We will use these novel laboratory data to test the world's leading computer code that is used to model the central regions of galaxies close to their black holes.