Understanding Quasar Outflows

点击翻译按钮获取中文摘要

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.