Supernova Remnants

Cassiopeia the queen sits low in the north-northeast at nightfall, then wheels high to the north at first light. Its stars form a bright letter W, so it’s one of the easiest constellations to pick out.
It would have been a lot easier to pick out in 1572. A “new” star appeared near the W -- a star so bright that it was visible in daylight.
And about a century later, another new star flared to life not far away. There are only sketchy indications that it was ever seen. But today, astronomers know all about both stars -- they were blasting themselves to bits as supernovae. Astronomers know that because they can see and study the remains of both stars -- expanding bubbles of gas and dust.
The first star is known as Tycho’s supernova. That’s because it was studied in detail by Tycho Brahe, the leading astronomer of the time. The star exploded when the small corpse of a once normal star stole gas from a companion star. When enough gas built up, the star blasted itself to smithereens. Debr