English: G11.2-0.3 is a circularly symmetric supernova remnant that contains a dense, rotating dead star at its center, representing a textbook case of what the remnant of an exploding star should look like after a couple thousand years. When a massive star collapses, the outer layers of the star are blown away in an extremely energetic explosion. Depending on the mass of the original star, a dense object such as a neutron star or a black hole, can form and be left behind at the explosion's center. Such a neutron star, known as a "pulsar" when it rapidly rotates, can be kicked by the thermonuclear shock wave created when the star exploded, causing it to race through space at millions of miles per hour.