This remnant of an exploded star is gigantic. The remnant, which astronomers call Cassiopeia A, is eleven thousand light-years away from Earth and about ten light-years across. It was captured by Chandra, a NASA satellite that has been orbiting the Earth since 1999, detecting X-rays.
Astronomers calculated that the star exploded about 350 years ago. Massive stars, at least eight times as massive as the Sun, can die in a gigantic explosion. The core collapses and matter is hurled violently into the universe. Such a so-called supernova happens about once every fifty years in the Milky Way.
The remnant of a supernova is hot. Cassiopeia A is about fifty million degrees at the edge and emits X-rays. Using Chandra, astronomers mapped the chemical makeup of Cassiopeia. Silicon appears in this image as red, sulfur as yellow, calcium as green and iron as purple. The total mass of the iron is estimated to be about seventy thousand times the mass of the entire Earth. The shock wave from the explosion is a blue shell.
In the coming weeks, astronomers will again look at the remainder, this time with the new American-Italian telescope IXPE. It was launched last month and is now orbiting the Earth 600 kilometers away. IXPE will investigate the polarization direction of the X-rays emitted by Cassiopeia. That should reveal something about the structure and magnetic field of the remnant.