Chandra data of Circinus X-1 reveal a set of four rings that appear as circles around the neutron star, providing a rare opportunity to determine the distance to an object on the other side of the Milky Way galaxy. These rings can be seen in the composite image of X-rays from Chandra (red, green, and blue) with a visible light image from the Digitized Sky Survey. These rings are light echoes, which are produced when a burst of X-rays from the star system ricochets off of clouds of dust between Circinus X-1 and Earth. By combining the X-rays with radio data, astronomers can use relatively simple geometry to pinpoint the location of the intervening clouds and then Circinus X-1.

This image combines NASA/ESA Hubble Space Telescope observations with data from the Chandra X-ray Observatory. As well as the electric blue ram pressure stripping streaks seen emanating from ESO 137-001, a giant gas stream can be seen extending towards the bottom of the frame, only visible in the X-ray part of the spectrum.

1.2 “/pixel, 22.7×35.5 arcmin
North is 2¡ CCW from up
RA = 18h02m25.61s Dec = -23d01m26.9s