English: In a polar system such as the prototype AM Her, matter will overflow the Roche lobe of the companion star. However, the white dwarf possesses a strong magnetic field, which prevents the formation of a accretion disk. Instead, the overflowing material is directed by the magnetic field structure until it impacts on the surface of the white dwarf at its magnetic pole. Until impact, the material essentially free falls, thus reaching substantial velocities which are seen in the optical spectra. The collision generates a shock wave which is the source of hard (energetic) X-rays. Hard X-rays emitted in the direction of the white dwarf from the shock wave above its surface heat the local area around the pole sufficiently for the pole to become a source of intense soft (less energetic) X-rays. Since soft X-rays are coming only from the pole, rotation of the white dwarf can occult the X-ray source on its surface. Polars are generally much stronger sources of soft X-rays than hard X-rays. Most likely, this is due to uneven matter streaming. Clumps in the accretion flows would most likely cause energy to also be liberated deep within the atmosphere of the white dwarf, resulting in more soft X-ray emission. The strong magnetic field will also lock the orientation of the white dwarf relative to the companion, so that orbital and rotational periods are identical. X-ray emission from polar systems is entirely due to the accretion column and its impact, so in quiscient times when matter is not accreting onto the system, the entire system is much dimmer. Spectral lines measured at these times show the Zeeman effect which measures the magnetic field strength in the megagauss range.