# Speed of blast from supernova

How fast does the blast front of a supernova expand at? Is it close to the speed of light or is it less than a quarter of the speed of light?

The speed of the blast front depends on the initial energy release and the density of the medium into which it is expanding, see here.

Theory suggests and measurements confirm expansion rates of the order of thousands of km/s or a few $\times 10^6\ \mbox{m/s}$ or $\sim 1\% \mbox{c}$.

• The initial velocity of the blast wave is quite a bit larger, more like 10,000 to 30,000 km/s, i.e. ~10% of the speed of light. Still less than a quarter of the speed of light, though. – pela Jul 22 '15 at 10:32
• Crab nebula, remnant of SN 1054, is still expanding at 1,000 kilometers per second: apod.nasa.gov/apod/ap130905.html – Wayfaring Stranger Jul 22 '15 at 12:08