Reverse Shock Wave Keeps Tycho’s Supernova Bright

In 1572, Danish astronomer Tycho Brahe noticed a bright new body that had appeared in the heavens. He called it a new star—stella nova—though it was actually the explosive end of a very old one—what we now call a supernova.

Today, Tycho’s supernova still burns bright, despite having first appeared hundreds of years ago. It’s been something of a mystery, though astronomers Hiroya Yamaguchi and Randall Smith now think they know why the explosion hasn’t flamed out.

Tycho's supernova, as seen by the Chandra X-ray Observatory

A reverse shock wave—caused when the initial shockwave from the explosion hit interstellar gas surrounding the former white dwarf—is ripping through the star’s remnants, heating the remaining gas and causing throw off x-rays. Here’s John P. Millis, writing for RedOrbit:

This is significant because of the reverse shock were to cease, or not arise in the first place, the inner volume of the remnant would fade much more quickly – a phenomenon that has been observed in other systems. “Thanks to the reverse shock, Tycho’s supernova keeps on giving,” says Smith.

Yamaguchi and Smith don’t know how, exactly, the electrons involved in the fluorescence are heated, but they plan to study other supernovae to find out.