System 8
System 8 is a rare system and astrophysically very interesting. It consists of two binaries orbiting one-another. Apart from a binary between an F star and an M star in a circularised synchronous orbit, there is a close binary consisting of a white dwarf and a brown dwarf, with an orbital separation of approximately 298 thousand kilometers. At this separation the brown dwarf is overflowing its Roche lobe, which has a calculated radius of 46 600 km (less than one Jupiter radius), which means it is losing matter stripped from it by the gravitational pull of the white dwarf. The white dwarf was formed from a supernova event some 10 million years ago. The gas ejected formed a double-lobed shell of gas which is now much faded but still detectable at this range as a diffuse shell of matter drifting into deep space. The brown dwarf gained some of the dying star's matter in this process, heavy elements originating from the shed envelope of the dying star are still detectable in the brown dwarf's atmosphere. The brown dwarf is cool enough to have a weak magnetic field, causing it to lose coupling to the white dwarf. (In many close binaries the two stars are magnetically linked as their magnetic fields interact like two bar magnets). Such coupling would lock the spins of the two stars, but their absence in this case has caused the white dwarf to spin-up, that is to rotate faster as it accreted matter from the brown dwarf, increasing its angular momentum. The white dwarf is currently rotating once every 36 seconds.

With the passing of time the white dwarf exceeded a critical rate of rotation at which it could no longer accrete most of the matter from the accretion stream, but instead ejected the matter from the system: this system is a so-called propeller system. The movie below is a time-lapse recording of three minutes of mass transfer. The blobs of plasma streaming from the atmosphere of the brown dwarf are moving at a mean speed of 948 km/s at their closest approach to the white dwarf. The matter continues to spiral into deep space.

Essentially, the white dwarf is dragging its magnetic field around with it. This magnetic field becomes stronger nearer to the white dwarf. Thus, as the blobs of matter fall towards the white dwarf, under the influence of its gravity, there comes a point when the ram pressure of the in-falling stream of matter becomes insufficient to cross the magnetic field of the white dwarf. Instead the charged particles of plasma spiral around the magnetic field lines of the white dwarf, but as these field lines are rotating fast, they impart angular momentum to the blobs and propel them out into deep space. Currently, only about 1% of the incoming matter reaches the white dwarf surface.
System 8
propeller system animation
Eventually, the white dwarf will lose angular momentum as it propels the blobs of plasma from the system: it is gradually spinning down. There will come a point at which more of the matter is able to reach the white dwarf's surface, causing it to spin-up again and eject the matter. It is expected to repeat this cycle until the brown dwarf is no longer over-filling its Roche lobe.

Sensors detect a total of 90 planets in this system, but only nine of those remain bound. The remaining 81 were probably former bound planets and moons which became ejected both as the orbits in this double-binary settled down (many of the orbits would have been transient and unstable) and also when the primary star passed through the red giant and supergiant stages and finally going supernova, disrupting most of the planetary orbits. Of those planets still bound, the M-class planet with five satellites, orbiting the M-F binary is sufficiently warm for life, with a mean surface temperature of 8.8 Celsius. It was probably warmed by a planetary collision. However, it is so remote from its stars, that it will likely freeze over before life manages to evolve upon it.

Recommendation: remain for one circadian cycle to make measurements of accretion stream and orbital kinetics to refine our computer models of propeller systems and then set a new course. In particular, we would like to analyse the fluid plasma motion and test theories on how easily the blobs of matter disrupt into a particle fluid upon passing the white dwarf. We would like to test the effects of Kelvin-Helmholtz instability and the effects of magnetic drag on the plasma flow.