"Our galaxy's last naked-eye supernova was Kepler's supernova, appearing back in 1604. This type Ia supernova arose from an exploding white dwarf 17,000 light-years away. After brightening and then fading away, the supernova remnant was discovered in the 20th century. Then, in 2000, NASA's Chandra X-ray observatory began surveying it. It revealed many features, including a circular - but asymmetric - blast wave. Chandra returned to view it repeatedly: in 2004, 2006, 2014, and 2025."
"This 25 year observational baseline represents 6% of the supernova remnant's cumulative age. The supernova's shockwave expanded by 0.5 light-years over that time: roughly 2% the speed of light. The northern expansion is slowest, at 1800 km/s, with southern expansion the fastest, reaching 6200 km/s. Faster speeds require lower-density mediums, implying an asymmetric surrounding environment. The blast wave's width is also measurable, showcasing Chandra's prodigious, enduring capabilities."
Nearby astronomical transients provide observable evolution on human timescales. Kepler's supernova, a Type Ia from an exploding white dwarf 17,000 light-years away, appeared in 1604 and left a remnant discovered in the 20th century. NASA's Chandra X-ray Observatory began surveying the remnant in 2000 and returned in 2004, 2006, 2014, and 2025. A 25-year observational baseline represents about 6% of the remnant's age. The shockwave expanded roughly 0.5 light-years over that interval, at about 2% the speed of light. Expansion speeds vary from 1,800 km/s in the north to 6,200 km/s in the south, indicating an asymmetric, lower-density environment in faster regions. The blast wave width is measurable due to long-term Chandra capabilities.
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