The evolution of the magnetic interaction between stars, discs, and planets

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Some of the most intense solar fireworks have directly affected modern life on Earth. Rapid increases in solar activity sends fluxes of charged particles towards our planet, giving rise to Aurora and disrupting satellite communications. Yet however spectacular the events on our Sun may seem today, our middle-aged star is comparatively quiet, and hides an even more violent past. A few billion years ago the Sun was a contracting ball of hot gas, although it was still too cool within its core to fuse hydrogen into helium and shine as it does today. Young solar analogues, called T Tauri stars, are about a million times too faint to be seen with the naked eye. Space satellite observations, however, have shown that they are typically 1000 times more active in X-rays than the Sun is presently. They are surrounded by large dusty planet-forming discs, which are bombarded by X-rays arising from violent stellar magnetic events. T Tauri stars are new-born stars which are still shrinking down under gravity to their adult proportions. As such stars collapse they should start to spin faster and faster, just like an ice-skater who pulls their arms in closer to their body. However, such stars are observed to be spinning slowly, an effect that has been attributed to how their strong magnetic fields interact with the gas and dust within their planet-forming discs. T Tauri stars are embedded in a web of magnetic field which binds them to the gas and dust within the disc. It is expected that this magnetic web acts as a brake, allowing the star to remain spinning slowly. This process, however, is poorly understood. Using a technique called Zeeman-Doppler imaging I have been able to determine the structure of their magnetic webs. This technique has strong parallels to the tomographic methods applied to construct 3D images of internal organs of the human body. This newly available data signals the beginning of a fresh era of research in to the formation of solar-like stars. My research will exploit this new stream of data, to investigate how forming stars interact with, and disrupt, their circumstellar environments. Ultimately this work will provide insight into the formation of our own Sun, and Solar System, at a time when the planets were just beginning to form. Roughly 300 planets have now been found orbiting other stars. It recently been discovered that some of these stars twinkle on the same timescale as it takes their planets to complete an orbit. This effect may be caused by highly energetic particles crashing into the stellar surface after being accelerated along strands of the magnetic web connecting the planet to the star. I will investigate this process in detail during the STFC fellowship.