Remnants from the explosions of stars in the 16th and 17th centuries are seen today.
Tycho Brahe’s observations of a supernova that flashed into view in 1572 are standard astronomical lore. Now astronomers have seen for themselves the light that Tycho saw 436 years ago. Some of the light from that exploding star 10,000 light-years away has been bouncing around our galaxy, scattering off dust clouds, and only now has it reached Earth. So too has light from another well known supernova – Cassiopeia A (Cas A).
As announcements from two research teams pointed out last month, the ability of modern telescopes to observe these faint and fleeting light echoes is a kind of time machine. It reveals what happened in an old supernova explosion when the opportunity for direct observation seems long gone.
The gaseous remnant of Cas A 11,000 light-years away is one of the most thoroughly studied objects in our galaxy. Astronomers would love to know what happened when its star blew up. It would let them trace the evolutionary journey from the unknown circumstances of the explosion to the well-known circumstances of the remnant they know today. Now they are getting the kind of data they need to find out.
Such knowledge is basic for understanding the evolution of planetary systems and even of organic life itself. Many key elements we take for granted on Earth were formed as shock waves from supernova explosions plough through the interstellar medium. They include such elements as bone-building calcium or tool-forming iron.