Understanding Quasar Outflows

想象一下，从我们的太阳系缩小，越过行星，超越我们银河系中的所有恒星。回过头来看看银河系，你会看到恒星和巨大的煤烟氢气云团和痕迹分子，它们正在慢慢坍塌形成新的恒星。你在其他任何地方都能看到的微弱光点不是恒星，而是整个遥远的星系。放大其中任何一个星系的中心，你会发现一大群恒星，如果星系足够大的话，还有一个质量相当于数百万甚至数十亿个太阳的黑洞。观察那个星系中的一个气体云，它太靠近黑洞了。引力将气体云拉伸成一个比我们太阳系更大的气体盘，以令人难以置信的速度绕轨道运行，但缓慢地向内螺旋，与黑洞共生。在内盘，摩擦使气体在比太阳表面大数百万倍的区域内比太阳热。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。这种旋转的高温气体的湍流吸积盘经常向上抛出气团，气团被来自内部盘的光向外推。这些团块形成了螺旋状的气体流，在某些方向上挡住了内盘的视线，并竞相进入拥有类星体的星系。这些快速移动的外流可以逆转供应吸积盘的气云流入，关闭吸积过程，关闭类星体。它们甚至可以震撼加热并吹出银河系中几乎所有的气体，结束恒星在银河系中的形成，并彻底改变其未来的外观和环境。我的研究团队和我的合作者正在调查类星体的外流，研究它们的时间变异性，并将它们与计算机模拟进行比较。我们正在研究类星体和它们的外流是如何工作的，这样我们就可以完善上面概述的图像，并改进我们关于星系形成和发展的模型。我们的目标也是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比我们使用超新星更早的时间上的暗能量历史。如果是这样的话，这将是对暗能量的一次有用的新测试，一种加速我们宇宙膨胀的神秘力量，也是当今科学界最大的谜团之一。

Imagine zooming out from our solar system, past the planets, beyond all the stars in our Milky Way galaxy. Look back at the Milky Way, and you'll see stars and giant, sooty clouds of hydrogen gas and trace molecules which are slowly collapsing to form new stars. The faint points of light you can see everywhere else you look aren't stars, but entire distant galaxies. Zoom into the center of any of those galaxies; you'll find a swarm of stars and, if the galaxy is big enough, a black hole with the the mass of millions or even billions of Suns. Watch as one of the gas clouds 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 spiraling 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. These clumps form spiraling 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 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.