This sequence of Chandra images, taken over nearly a decade and a half, captures motion in Kepler's supernova remnant. Pieces of this debris field are still moving at about 23 million miles per hour over 400 years after the explosion was spotted by early astronomers. Scientists are still trying to determine whether an extremely powerful explosion or an unusual environment around it is responsible for these high speeds so long after the explosion. The Kepler supernova was triggered by a white dwarf that reached a critical mass after interacting with a companion star and exploded.

This pair of illustrations shows the motion of three clumps of matter ("knots") in Kepler's Supernova Remnant between 2000 and 2016. This view is looking down on the remnant and Chandra's line of sight from above. The location of the explosion's blast wave at these times is shown, and a cross depicts where the supernova occurred. Chandra spectra obtained in 2016 depict X-ray emission from silicon in each knot. The emission line is shifted to shorter and bluer wavelengths than the laboratory value (dashed line) for the knot moving towards Chandra, and to longer and redder wavelengths for the two knots moving away from Chandra. The knot on the right undergoes less motion along Chandra's line of sight and is redshifted less. Motions of the knots from left to right or vice versa are also visible from Chandra's point of view. The speed of motion of the knots and the line of sight motion determined from the spectra combine to give their total speed.