The Light Echoes Settle It
June 23rd, 2015, 6:10PMMeasuring distances over the vast reaches of the galaxy can be difficult for astronomers, but sometimes they get a little help. These huge rings of light (see image) are called “light echoes,” and emanate from an X-ray blast produced by the double star system Circinus X-1 in 2013. The X-ray energy is now reflecting off nearby dust. NASA’s Chandra X-Ray Observatory has been taking sensitive measurements of the system, which has allowed astronomers to triangulate its location, similar to the way bats use sonar. The results have settled a debate on its distance: 30,700 light years away, twice as far as a previously published distance.