SR is short for Synchrotron Radiation. It's emitted when a charged particle encounters a strong magnetic field. The particle then accelerates along a spiral path following the magnetic field and emitting radio waves in the process. The result is a distinct radio signature revealing the strength of the magnetic field.
SR is produced by the spiraling electrons along Birkeland currents. Non-relativistic moving particles produce radiation called cyclotron emission. Cyclotron radiation is electromagnetic radiation emitted by accelerating charged particles deflected by a magnetic field. The Lorentz force (F = qE +qv X B) on the particles is perpendicular to both the magnetic field and the particles' motion through them. The force makes the charged particles accelerate and, therefore, emit radiation as they spiral around the magnetic field lines.
This radiation originates from the cyclotron – a particle accelerator that produces highly energetic particles. The cyclotron makes use of the circular orbits taken by charged particles in a uniform magnetic field.
The orbit period is independent of particle energy, permitting the cyclotron to operate at a set frequency. Cyclotron radiation is emitted by all charged particles traveling through magnetic fields, not just those in cyclotrons.
Radiation from plasma in the interstellar medium provides information about distant magnetic fields.
Synchrotron emission is generated by astronomical objects around which relativistic electrons spiral (and hence change velocity) through magnetic fields. The radiation produced has a characteristic polarization, and the frequencies generated can range over the entire electromagnetic spectrum. This radiation is called continuum radiation.
In astrophysics, synchrotron emission is said to occur due to the ultra-relativistic motion of sources around so-called ‘black holes.’ Those are fictitious entities that conveniently can't be seen! When the source performs a circular geodesic around a black hole, the synchrotron radiation occurs for orbits close to the photosphere where the motion is in the ultra-relativistic regime. A geodesic, by the way, is a “straight line” in curved spacetime.
What a load of nonsense! It’s mathemagics and an unverifiable thought experiment. Spacetime is a mathemagical construct with no presence in physical reality. How does matter tell space and time how to curve? Indeed, what does it mean to curve time when it has no physical dimension or direction?” It's laughable. The word 'space' signifies locations in three-dimensions, so how can a fabric of spacetime be woven out of non-physical concepts? No wonder main steam astroscience is so mysterious to laypeople.