By Ron Cowen
In 1572, the Danish astronomer Tycho Brahe created a sensation when he reported that a star suddenly appeared in the sky, blazing brighter than Venus, and then faded from view. Tycho’s “new star” was in fact a supernova, an exploding old star. More than 4 centuries later, observations of the remnant of Tycho’s supernova are still revealing information to astronomers. High-resolution X-ray images now offer evidence that shock waves from that and other supernovas generate most of the cosmic rays that bombard Earth.
X-ray images taken a decade ago showed that shock waves from supernova remnants can accelerate electrons to cosmic ray energies, but electrons make up only about 10 percent of cosmic rays. Energetic ions, the main component of cosmic rays, don’t generate much light and are much more difficult to trace than electrons. Some cosmic ray researchers have presumed that these heavier cosmic particles also have a supernova origin, but astronomers have had scant evidence.