Watch a real supernova blast evolve over 25 years in new telescope video

Astronomers have turned a famous star explosion into a 25‑year time‑lapse, using a NASA telescope to watch the superheated gas race through space and slam into its surroundings. 

The new study using the Chandra X-ray Observatory tracks how different parts of the shockwave slow down in different directions, turning this 400‑year‑old relic into a laboratory for how supernovas work.

The stakes go beyond a striking movie, which you can watch further down in this story. 

The explosion, known as Kepler’s Supernova Remnant, was a kind of exploding star that astronomers use to measure cosmic distances because it gives off a predictable brightness. By watching how this shock front changes speed, researchers can learn how the messy, real environments of so-called Type Ia supernovas shape their behavior.

The observations also help refine how much astronomers can trust Type Ia supernovas as cosmic yardsticks.

"It's important that we understand these events because (they help) cosmologists measure the expansion of the universe," said Jessye Gassel, a George Mason University graduate student who presented the results at the 247th American Astronomical Society meeting in Phoenix this week. "There's still a lot unknown about these Type Ia explosions and how they happen."

German astronomer Johannes Kepler first spotted this supernova remnant in the constellation Ophiuchus in 1604. At the time, Kepler believed it was a new star, but scientists now know it as the dazzling aftermath of a star explosion roughly 17,000 light-years from Earth. 

It's the last clearly observed supernova in the Milky Way, Gassel said. 

Chandra-X has looked at the remnant since 2000, capturing about 6 percent of its lifetime. Gassel's team stitched those observations into the longest X‑ray movie the telescope has ever made, showing its evolution from 2000 to 2025. Frame by frame, the outer shell swells, revealing bright filaments where the shockwave — the high‑speed front of material and energy from the explosion — invades surrounding gas, heating it to millions of degrees.

Over the course of the quarter-century that the telescope has watched the aftermath, the shockwave has covered a great distance, traveling half a light-year, or about 3 trillion miles. 

The team measured how fast this border moves in different regions. In some directions, the blast surges ahead at roughly 14 million mph. In others, it slows to about 4 million mph. That contrast suggests the explosion is not expanding into uniform, empty space. Instead, one side runs into relatively thin gas, while the other rams into much thicker material. 

You could think of it like a jeep excursion. In one direction, it has a clear highway to traverse. In another, it's off-roading. The jeep with the paved road can drive much faster than the jeep slogging through mud. 

"Kepler Supernova Remnant is pretty spherical, but since we know that there (are) different densities surrounding it, we wouldn't expect it," Gassel said. "What's happening is, even though there are different densities that the blast wave (is) running into, the location of where the star exploded is actually moving, instead of having a warped shape at the edges." 

The pattern reflects what the star system was doing before it blew up. A Type Ia supernova occurs when a white dwarf — the Earth‑sized core of a dead star — orbits a companion star. As that system evolves, it can shed gas into the space around it. The uneven shock speeds in Kepler’s remnant map out how much material piled up in different directions, providing a record of the system’s history.

Though Type Ia supernovas remain reliable distance markers for the universe's expansion, they're not all perfectly identical. This kind of study can help scientists understand how the local environment can account for subtle differences. 

Because the Chandra-X mission won't go on forever, astronomers may only have another decade to watch the supernova remnant unfold. But successors, such as the potential AXIS X-ray satellite, could continue to monitor this and other explosions.