If the star is massive enough, it will explode at the end of its existence. What remains after this “supernova explosion” is a huge, expanding gas cloud. Located in the constellation Cassiopeia, this stellar remnant exploded over eleven thousand years ago. In 1670, its light first reached Earth.
The gas cloud is expanding at a rate of 6000 kilometers per second and is currently about sixteen light years across. This means that light takes 16 years to travel from one side of the gas cloud to the other. In contrast, light takes 8 minutes to reach the Earth from the Sun. These unimaginable proportions present tricky mysteries: new research shows that some parts of the nebula move against the direction of the explosion, while other parts are accelerating rather than decelerating gradually.
According to the researchers, the explanation is that the expanding nebula collided with something. Perhaps this “thing” is an envelope of gas particles surrounding the nebula, which the star blew out before the explosion.
By the way, the amazing colors of this cloud are not “real”. Much of the gas cloud is invisible to the human eye, forcing researchers to add colors to keep visualizing those parts.
