System 89
This system has no detected planets (the possibility of small and hard to detect dwarf rogue planets existing on the edge of the system
can never be entirely ruled out). The system consists of a
white dwarf orbiting with a hot whitish F-class star.  Existing by itself, an F-class
star is a good candidate for a planetary system, due to the presence of sufficient mass in the protostellar nebula and the fact that
F-class stars are not so hot as to evaporate all this material before planets form. However, the death of the star that is now a cooling
white dwarf may have incinerated any planets in this system. The planetary nebula material has also swept past the F-star (dotted line
indicates the inner edge of this material) and this star probably accreted some of this material, enlarging itself.

The white dwarf is unusually large (at 1.43 solar masses) and very close to the maximum or Chandrasekhar mass limit for a white dwarf
(the precise limit depends upon chemical composition). Had it retained slightly more mass, when it formed, then we would expect it to
have become a neutron star. Stellar wind-driven mass transfer is now occurring in this system, with the white dwarf accreting mass from
the stellar wind of the F-star. As the F-star leaves the main sequence and becomes a red giant and supergiant and begins to blow-off its
outer atmosphere in a superwind, then the rate of mass accretion by its white dwarf companion will increase. At some point, either before
or after the F-star reaches this stage, the white dwarf will likely accumulate enough mass to exceed the Chandrasekhar limit at which
point it is expected to detonate in a thermonuclear explosion as a type 1a supernova. The precise limit is unknown and varies slightly
according to the physical model employed. To be honest, this star could detonate at any moment!

Although the drag imposed by the planetary nebula gases on the F-star would have reduced the separation between the two stars, it was
insufficient to cause the F-star to fill its Roche lobe and thus there is no accretion stream driving the formation of an accretion disc about
the white dwarf.

The data obtained from the ship's sensors should help us to understand better white dwarfs close to the Chandrasekhar limit and help
refine our estimates of this critical mass.

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