Astronomers at NASA the Chandra X-ray Observatory are using light echoes to work out the distance of an object far beyond the limits of Earth. The technology is very much like the one bats use to locate how far an object is in dark caves. The trick is called echolocation. The creature, although not blind as it commonly thought by people, uses its mouth to create sounds that bounce off nearby objects, such as a moth.
The main difference is that while bats you sound waves, NASA is using rainbow X-rays for the purpose.
Circinus X-1 is a binary star system located at the other end of the Milky Way from us. It contains a neutron star that regularly emits bursts of X-rays.
The bright spot in the centre of the image above is one of its intense X-ray flares, observed in 2013.
The four brightly-coloured rings surrounding it represent echoes of the original signal, formed when bursts of radiation bounced off dust clouds en route to our vantage point. Eventually they reached us, after a delay of several months. (The sharp cut-offs on the image are a result of the detector orientation on the Chandra telescope, which prevents them from providing a continuous map of the sky.)
Sebastian Heinz from the University of Wisconsin in Madison and his team combined this image with radio data revealing the distance to the four dust clouds to work out the distance to Circinus X-1 with more accuracy than ever before.
According to the new analysis, it is 30,700 light years away from Earth. This resolves a large discrepancy in previous results: one measurement gave a similar distance, but another claimed it was just 13,000 light years away.
Light echoes from a supernova have recently helped create a 3D map of its host galaxy. Cosmic echoes bouncing around the universe could also hold clues about the very early universe, shortly after the big bang.