The light of supernova SN 1604 first reached Earth 416 years ago, described by the German astronomer Johannes Kepler, after whom it is named. Kepler’s supernova now appears as an expanding nebula, and after four centuries, shows no sign of slowing down at all.

New observations of the expanding supernova remnant have been published in The Astrophysical Journal, revealing one piece was recorded moving away from the star at astonishing speed. The team looked at 15 “knots,” blobs of debris in the nebula, measuring how fast they are moving. The fastest observed is traveling with a velocity of up 37 million kilometers per hour (23 million miles per hour).

Such high speed was previously determined using data from the same telescope, NASA’s Chandra X-ray observatory, but with a different instrument. This independent confirmation shows that this supernova was extremely powerful and that the expanding nebula has barely been slowed down by interaction with interstellar material.

The data from Chandra also revealed hints at possible asymmetry in the distribution of matter around the supernova remnant. Eight of the 15 knots are certainly moving away from Earth. Only two are moving towards us and the other five haven’t got a clear direction.

Fifteen knots is too small a number to confirm if the nebula can expand more easily away from us than towards us. More observations will be necessary to clarify that.

SN 1604 is located 6,000 light-years away in the constellation of Ophiuchus. It is believed to be a Type Ia supernova, an unusually powerful kind of stellar explosion. These happen when a white dwarf, the exposed core of an evolved star, steals enough material from a companion that it collapses under its own weight. The resulting explosion has a characteristic luminosity and so can serve as a “standard candle,” a way for scientists to measure intergalactic distances.

Back in 1604, the event was called a Stella Nova, Latin for "new star". It shone so brightly at first that for three weeks it was visible to the naked eye during the day.