Constraining the Properties of Quasars and their Outflows Using Variability

想象一下我们的太阳系和银河系中的所有恒星之外的航行。那时你能看到的微弱光点就不是恒星了，而是整个遥远的星系。在任何一个星系的中心，你都会发现一群恒星，如果星系足够大，还会发现一个质量相当于数百万甚至数十亿个太阳的黑洞。注意，该星系中的一团氢、氦和微量元素云太靠近黑洞了。引力将气体云拉伸成一个比我们的太阳系更大的气体盘，以令人难以置信的速度绕轨道运行，但慢慢地向内螺旋，并与黑洞吸积。在内盘中，摩擦使气体比太阳更热，面积比太阳表面大数百万倍。 这个巨大的，发光的圆盘可以在整个宇宙中看到，我们称之为类星体。这种由高温旋转气体组成的湍流吸积盘经常会抛出气体团，这些气体团被来自内部盘的光向外推。这些团块形成螺旋状的气体流，在某些方向上阻挡了内部盘的视线，并迅速进入类星体所在的星系。这些快速移动的外流可以逆转供应吸积盘的气体云的流入，关闭吸积过程并关闭类星体。它们甚至可以冲击加热并吹出星系中几乎所有的气体，结束星系中星星的形成，并彻底改变其未来的外观和环境。我和我的研究团队和合作者正在调查类星体的外流，研究它们的时间变化，并将它们与计算机模拟进行比较。我们正在研究类星体及其外流是如何工作的，这样我们就可以完善上面概述的图片，并改进我们关于星系如何形成和发展的模型。我们还旨在帮助确定我们是否可以利用类星体大小和光度之间的关系来追溯暗能量的历史，而不是我们可以利用被称为超新星的爆炸恒星。如果是这样，那将是对暗能量的一个有用的新测试，暗能量是一种加速宇宙膨胀的神秘力量，也是当今科学中最大的谜团之一。

Imagine voyaging out of our solar system and beyond all the stars in our Milky Way galaxy. The faint dots of light visible to you then then wouldn't be stars, but entire distant galaxies. At the centre of any of those galaxies you'll find a swarm of stars and, if the galaxy is big enough, a black hole with a mass of millions or even billions of Suns. Watch as one of the clouds of hydrogen and helium gas and trace elements in that galaxy ventures too close to the black hole. Gravity stretches the gas cloud into a disk of gas bigger than our solar system, orbiting at incredible speeds but slowly spiralling inwards to accrete onto the black hole. In the inner disk, friction makes the gas hotter than the Sun over an area millions of times larger than the Sun's surface. That enormous, glowing disk can be seen all the way across the universe, and we call it a quasar. This turbulent accretion disk of hot, rotating gas often tosses up gas clumps which are pushed outward by the light from the inner disk. The clumps form spiralling streamers of gas which block the inner disk from view in some directions and which race out into the galaxy hosting the quasar. These fast-moving outflows can reverse the inflow of gas clouds supplying the accretion disk, shutting down the accretion process and turning off the quasar. They can even shock-heat and blow out almost all the gas in the galaxy, ending star formation in it and drastically changing its future appearance and environment. My research team and collaborators and I are surveying quasars for outflows, studying their time variability, and comparing them to computer simulations. We are learning how quasars and their outflows work so that we can refine the picture outlined above and improve our models of how galaxies form and develop. We also aim to help determine whether or not we can use the relationship between quasar size and luminosity to trace the history of dark energy farther back in time than we can with the exploding stars known as supernovae. If so, that would be a useful new test of dark energy, a mysterious force accelerating the expansion of our universe and one of the biggest mysteries in science today.