However, electrons and protons are charged particles. When travelling through interstellar space, the direction of their travel is influenced by the magnetic field of the Milky Way Galaxy. The known forms of radiation are electromagnetic and gravitational. Gravitational radiation results from the acceleration of massive objects. Gravitational radiation has never been detected directly, and its indirect detection resulted in the 1993 Nobel Prize.
Gravity is a much weaker force than electromagnetism.
Thus, detectable amounts of gravitational radiation result only from events like the explosion of a massive star or the gravitational interaction between two closely orbiting neutron stars or black holes. Again, it is possible that a future technology might result in gravitational radiation becoming easier to detect. It is still difficult to imagine that it would not also result in electromagnetic radiation. Gamma rays are extremely energetic and are produced by events like the explosion of nuclear bombs. Radio radiation is far less energetic.