A supernova that once rivaled Venus in the sky has a unique reason for being so observable: a reverse shockwave speeding back towards the explosion's center at speeds of up to Mach 1000.

Mach 1000 translates to around 340,000 meters per second, or around 760,000 miles per hour. Cosmic proportions, no matter how you look at it.

"We wouldn't be able to study ancient supernova remnants without a reverse shock to light them up," says Hiroya Yamaguchi, a research team member from the Harvard-Smithsonian Center for Astrophysics (CfA).

Supernovas, which are the brilliant explosions of a dying star, can light up an entire galaxy and emit as much energy as the sun does in an entire lifetime in one instant. The actual explosion is short-lived, but the remnants and stellar material can be seen for hundreds of thousands of years later. While there are many possible reasons for the visibility of a supernova's aftermath, it seems a Mach 1000 reverse shockwave is causing the supernova remnants of the Tycho supernova to heat up and emit X-ray light.

"It's like the wave of brake lights that marches up a line of traffic after a fender-bender on a busy highway," explains Randall Smith, also from the CfA. "Thanks to the reverse shock, Tycho's supernova keeps on giving."

The Tycho supernova was discovered by astronomer Tycho Brahe in 1572, and at its peak was as luminescent as Venus in the night sky. Tycho is believed to have been caused by the explosion of a white dwarf star, when innumerable amounts of cosmic matter were ejected at speeds of 11,000,000 miles per hour. Tycho's outward-traveling shockwave is still chugging along today at speeds of up to Mach 300.

The findings concerning the Tycho supernova and its Mach 1000 reverse shockwave have been accepted for publication in The Astrophysical Journal.