In 1604, German astronomer Johannes Kepler spotted a new star in the sky that was so bright it could be seen during the daytime. The discovery, which Kepler described in his book *De Stella Nova*, caused quite a stir in the astronomical community. With this one point of light, astronomers questioned the prevailing dogma that the "firmament" (the background stars in the sky) was not unchanging and permanent. In time, we would come to realize that Kepler's Supernova (as it's come to be known) was a white dwarf that exceeded its critical mass and exploded in a brilliant burst.
Located about 17,000 light-years from Earth in the constellation Ophiuchus, Kepler's Supernova is a prime example of a Type 1a supernova. These occur when a white dwarf in a binary system pulls material from its companion star or merges with another white dwarf. Its proximity to Earth has allowed the Chandra X-ray Observatory to capture detailed images of the supernova remnant, which astronomers have used to monitor its evolution over time. Based on data acquired between 2000 and 2025, the science team has created the longest-spanning video of the debris field left by this supernova.
Supernova remnants, which consist of massive clouds of dust and gas expelled from the star, are heated to millions of degrees by the heat of the explosion. This causes the material to glow brightly in different wavelengths (often in X-ray light), which Chandra has monitored using its advanced X-ray optics. Combined with the longevity of the mission, which has been in operation for a quarter of a century, Chandra has monitored changes in the remnant cloud very closely.
Jessye Gassel, a graduate student at George Mason University in Virginia, led the work on this video. It and the associated research were presented by Gassel at the 247th meeting of the American Astronomical Society in Phoenix. "The plot of Kepler’s story is just now beginning to unfold," he said in a Chandra press release. "It’s remarkable that we can watch as these remains from this shattered star crash into material already thrown out into space."
A particularly interesting part of this video is how it shows different parts of the remnant moving at incredible speeds in different directions. While the fastest parts are traveling at about 2% the speed of light (22.2 billion km/h; 13.8 billion mi/h) downwards, the slowest parts are traveling at 0.5% the speed of light (6.4 billion km/h; 4 billion mi/h) upwards. This difference is due to the gas the remnant is pushing toward the top of the image being denser than the gas it is pushing toward the bottom. This provides scientists with information about the supernova's environment.
Another interesting feature is the widths of the rims forming the blast wave of the supernova, the leading edge of the explosion that encounters material outside the star first. By examining how wide and fast it was, the team gained vital information about the star's explosion and its immediate surroundings before they were disturbed. "Supernova explosions and the elements they hurl into space are the lifeblood of new stars and planets," said Brian Williams, the principal investigator of the new Chandra observations. "Understanding exactly how they behave is crucial to knowing our cosmic history."
Further Reading: NASA
