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

一些最强烈的太阳烟花直接影响了地球上的现代生活。太阳活动的迅速增加向我们的星球发送了大量带电粒子，形成了极光，并扰乱了卫星通信。然而，无论今天太阳上发生的事件看起来多么壮观，我们这颗中年恒星相对平静，隐藏着更激烈的过去。几十亿年前，太阳是一个收缩的热气球，尽管它的核心仍然太冷，不能像今天这样将氢聚变成氦并发光。年轻的类似太阳的恒星被称为T金牛座恒星，它们的亮度大约是肉眼所能看到的100万倍。然而，太空卫星的观测表明，它们在X射线中的活跃度通常是目前太阳的1000倍。它们被巨大的尘埃行星形成盘包围着，这些盘被猛烈的恒星磁场事件产生的X射线轰击。金牛座T星是新诞生的恒星，它们在重力作用下仍在收缩，达到成年时的比例。当这样的明星崩溃时，他们应该开始越来越快地旋转，就像滑冰运动员把胳膊拉得更靠近身体一样。然而，人们观察到这类恒星的自转速度很慢，这一效应被归因于它们的强磁场如何与其行星形成盘内的气体和尘埃相互作用。金牛座T星嵌在一个磁场网中，磁场将它们与盘内的气体和尘埃捆绑在一起。预计这种磁网会起到刹车的作用，让恒星保持缓慢的自转。然而，人们对这一过程知之甚少。使用一种名为塞曼-多普勒成像的技术，我已经能够确定它们的磁网的结构。这项技术与用于构建人体内部器官3D图像的断层扫描方法有很强的相似之处。这些新获得的数据标志着研究类太阳恒星形成的新纪元的开始。我的研究将利用这一新的数据流，研究正在形成的恒星是如何与其周围的恒星环境相互作用和破坏的。最终，这项工作将提供对我们自己的太阳和太阳系形成的洞察，当时这些行星刚刚开始形成。现在已经发现了大约300颗围绕其他恒星运行的行星。最近发现，其中一些恒星的闪烁时间与它们的行星完成一周轨道的时间尺度相同。这种效应可能是由高能粒子沿着连接行星和恒星的磁网加速后撞上恒星表面造成的。我将在STFC团契期间详细研究这一过程。

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.