From NASA
March 23, 2021
More than 11,000 years ago, a massive, oversized star had reached the end of its life. The core of the star collapsed, forming an incredibly dense neutron ball. Its exterior has been blown away in an immense release of energy that astronomers refer to as a supernova.
The light of this supernova first reached Earth from the direction of the constellation Cassiopeia around AD 1667. If anyone living at that time saw it, they left no record. It is likely that large amounts of dust between the dying star and Earth dimmed the brightness of the explosion to such an extent that it was barely or not at all visible to the naked eye.
The rest of this supernova was discovered in 1947 due to its strong radio emission. Listed as Cassiopeia A, it is one of the brightest radio sources in the sky. More recently, the Far-Field Infrared Surveyor Explorer (WISE) discovered infrared echoes of the flash of light rippling outward from the supernova.
In the picture, the central bright dust cloud is the pressure wave that moves through interstellar space and heats up dust in the process. The pressure wave moves quickly – at about 6% the speed of light. By the time WISE captured this image, the shock wave had expanded approximately 21 light years from the original explosion. The flash of light from the explosion, which spreads at the speed of light, has traveled well over 300 light years. The orange echoes farther from the central remainder are from interstellar dust heated by the supernova flash centuries after the original explosion.
The wrong colors in this picture represent different wavelengths of infrared light, which is invisible to the human eye.
Photo credit: NASA / JPL-Caltech / UCLALast Updated: March 23, 2021 Publisher: Yvette Smith
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