The top image shows a smaller sphere apparently exploded from the top half of a larger half-shell, so how did IC 443 get this unusual shape, known as the “morphologically shaped supernova remnant?” mixed”? In a model created by the team, the supernova event (probably a Type II supernova) “occurred in a very inhomogeneous ambient environment, so the rest neutron star and pulsar wind nebula sit off-center (to the southeast) surrounded by a half-spherical atomic cloud and a donut-shaped molecular cloud, ”Ustamujic said.
During the first hundred years, the ejecta expanded relatively evenly. About 300 years after the event, however, it struck one side of the molecular ring, which slowed down the front shock wave and created a reverse shock. During this time, the part of the rest that did not touch anything continued as normal, while the part that struck the atomic half-sphere cloud slowed down.
Based on model (shown here in 3D), the researchers estimate the age of the remainder at 8,400 years. In its current state, the lower half has grown the most, creating the larger hemisphere shown in the image. The top part, meanwhile, was pinched on the sides by the donut and at the top by the atomic cloud, creating the smaller offset ball. The hottest parts of the rest with the most intense x-ray activity occur where the shock wave interacts with the cloud material.
The model explains the “very irregular and asymmetrical distribution” of the supernova remnant in a “natural way”, according to one paper by the team. As well as providing cool visualization, it could help future researchers understand the chemical distribution in IC 443 and similar supernova remnants.
Update 12/30/2020 3:00 p.m. ET: The article has been updated with comments from Sabina Ustamujic, lead author of the article.