![]() ![]() The blue arrows show the western section of the inner shell moving back towards the center of the nebula. But in the western region, the two shells are going in opposite directions: The outer shell is still expanding outward, but the inner shell is moving back toward where the exploding star would have been.Īn image of Cassiopeia A showing the shock wave move through the inner and outer shells of gas. These two shells are two halves of the same shock wave, and across most of the nebula, the inner and outer shells are traveling at the same speed and in the same direction. But over time, shock waves lose their momentum to their surroundings and slow down.Ĭassiopeia A consists of two main expanding bands of gas: an inner shell and an outer shell. ![]() This is mainly because the remnant is so young light from Cassiopeia A reached Earth in 1970. The current average speed of the expanding gas in Cassiopeia A is around 13.4 million mph (21.6 million km/h), which makes it one of the fastest shock waves ever seen in a supernova remnant, Vink said. The data, collected over 19 years, confirmed that part of the western region of the shock wave was, in fact, retreating in the opposite direction in a reverse shock.īut they also discovered something even more surprising: Parts of the same region were still accelerating away from the supernova's epicenter, like the rest of the shock wave. ![]() ![]() In the new study, the researchers analyzed the movement of the shock wave, using X-ray images collected by NASA's Chandra X-ray Observatory, a telescope that orbits Earth. ![]()
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