![]() "Either there is a hole somewhere, a kind of vacuum, in the supernova material, causing the hot shell to suddenly move inwards locally. "The backward movement in the west can mean two things," says Jacco Vink. ![]() The red arrows show that the other remnants do expand outwards. The blue arrows on the right (astronomers call this the west side) show that the inner shell is not expanding outwards at this point, but inwards. ![]() This outer shock wave turned out to accelerate in the west instead of decelerating as was expected.Īn image of Cassiopeia A showing only two shells of nebulae. The researchers also took measurements of the acceleration or deceleration of the outer shock wave. The scientists observed that on the western side of Cassiopeia A, the inner regions of the explosion nebula are not expanding, but moving inwards. This is an American X-ray satellite with Dutch spectrometers that orbits the Earth in a high elliptical orbit. The researchers, led by Jacco Vink (University of Amsterdam, the Netherlands) analysed 19 years of data from the Chandra X-ray Observatory. Cassiopeia A is now about 16 light years across. The expansion is most likely occurring in gas that was blown out by the star long before the explosion. ![]() The Cassiopeia A explosion nebula is expanding at an average rate of 4000 to 6000 kilometres per second and has a temperature of about 30 million degrees Celsius. However, there was too much gas and dust around the star for the explosion to be seen with the naked eye or with the then very basic telescopes. Light from the explosion should have reached Earth for the first time around 1670. Cassiopeia A is the remnant of an exploded star in the Cassiopeia constellation, about 11,000 light years away from us. ![]()
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