NASA | JPL-Caltech | Spitzer | 2016 Apr 26
[img3="Protoplanetary Disk (Artist's Concept) - Credit: NASA/JPL-Caltech"]http://www.spitzer.caltech.edu/uploaded ... 09_Med.jpg[/img3][hr][/hr]Imagine you want to measure the size of a room, but it's completely dark. If you shout, you can tell if the space you're in is relatively big or small, depending on how long it takes to hear the echo after it bounces off the wall.
Astronomers use this principle to study objects so distant they can't be seen as more than points. In particular, researchers are interested in calculating how far young stars are from the inner edge of their surrounding protoplanetary disks. These disks of gas and dust are sites where planets form over the course of millions of years. ...
Making the measurement wasn't as simple as laying a ruler on top of a photograph. Doing so would be as impossible as using a satellite photo of your computer screen to measure the width of the period at the end of this sentence.
Instead, researchers used a method called "photo-reverberation," also known as "light echoes." When the central star brightens, some of the light hits the surrounding disk, causing a delayed "echo." Scientists measured the time it took for light coming directly from the star to reach Earth, then waited for its echo to arrive. ...
Photo-reverberation Mapping of a Protoplanetary Accretion Disk around a T Tauri Star - Huan Y. A. Meng et al
- arXiv.org > astro-ph > arXiv:1603.06000 > 18 Mar 2016