Puppis A is now called a supernova remnant. It is about ten light-years in diameter. The explosion that caused Puppis A occurred about 3,700 years ago.

Referred commonly as a “Cosmic Cannonball,” RX J0822-4300 is estimated by astronomers to be on a course to take it out of the Milky Way galaxy in millions of years. It is a neutron star, or a star formed from the collapsed remnant of a massive star. Neutron stars are thought to contain mostly neutrons.

U.S. astrophysicist Robert Petre, of the NASA Goddard Space Flight Center (Greenbelt, Maryland), and U.S. physicist Frank Winkler, of the Department of Physics, Middlebury College (Vermont), were the two astronomers who used the Chandra X-ray Observatory over a five-year period to observe this extremely fast moving star. They say that astronomers have found over stars moving millions of miles per hour.

These stars, commonly called “hypervelocity stars,” are thought to gain their speeds from gravitational interactions with huge black holes. One such black hole at the center of the Milky Way galaxy is thought to have ejected stars on a course out of the galaxy at such fast speeds. However, RX J0822-4300 got its speed in a different way. It was ejected by the explosion of a supernova.