A relativistic speed is considered to be one that represents a significant percentage of the speed of light and that therefore makes it necessary to take into account the effects of special relativity.
This is apparently the case with many of the meteorites that reach Earth’s atmosphere.
A fraction of the speed of light
According to a new study by astronomers at Harvard University, meteors larger than single grains (between one to ten centimeters in diameter) could be the result of nearby supernovae that cause particles to accelerate to sub-relativistic speeds or even relativistic , several thousand times the speed of sound at a fraction of the speed of light.
As one of the study’s authors, Amir Siraj , explains:
Empirical evidence indicates that at least one supernova has precipitated heavy elements on Earth in the past. Supernovae are known to release significant amounts of dust at sub-relativistic speeds. We also see evidence of clumping or "bullets" in the supernova ejection. The mass fraction contained in small clumps is unknown, but if only 0.01% of the dust ejection is contained in objects of millimeter size or larger, we would expect one to appear in Earth’s atmosphere as a sub-relativistic meteorite. each month, based on the rate of supernovae in the Milky Way galaxy.
Meteorites generally travel about 0.01% of the speed of light. Supernova meteors would travel a hundred times faster (about 1% the speed of light).
All of this still remains at the theoretical level : an infrastructure that does not yet exist is needed that would allow astronomers to confirm the existence of these objects and study them.
The new studies could incorporate infrasound microphones and optical infrared instruments that could detect the acoustic signature and optical flashes, since a sub-relativistic meteorite would give rise to a shock wave that could be picked up by a microphone, and also a bright flash visible radiation.