A new form of stellar energy?

The X-ray source RX J1914+24 was discovered using ROSAT and was found to vary on only one period - 569 sec. Further work by astronomers at MSSL suggested that this period represented both the spin period of the accreting white dwarf and also the binary orbital period. This short period implied that the mass donating could not be a main sequence star as found in other accreting binary systems but had to be a white dwarf. RX J1914+24 was therefore proposed as a double degenerate polar: `double-degenerate' because both binary components were degenerate stars (white dwarfs) and `polar' because polars are accreting binary systems in which the accreting white dwarf has a magnetic field strong enough (10-200MG) to synchronise its spin period with the binary orbital period (see Cropper et al 1998) and Ramsay et al 2000).

However, further observations led by astronomers at MSSL found that two of the distingushing characteristics of polars - polarised optical light and optical emission lines - were absent Ramsay et al 2002). This paper proposes several other scenarios for RX J1914+24. These include a double degenerate Algol system (also proposed independently by Marsh & Steeghs 2002), a neutron star-white dwarf pair and a unipolar-inductor model (or electric star model). The latter model would represent a third form of stellar energy after nuclear and accretion power. It is described more fully in Wu et al 2002) .

This proposal may seem rather far-fetched. However, we do know that a similar effect has been observed on Jupiter where its satellite's rotate round the magnetic field of Jupiter causing electrical currents to be driven. These are deposited in the Jovian atmosphere causing bright streaks which were imaged using the Hubble Space Telescope:


This image shows both the aurora on Jupiter (caused by the same effect as the Northern lights we observe on Earth) and also the footpoints of three of Jupiters satellites. Each footprint is represented by a bright dot. Io's footprint is at far left; Ganymede's is just below and to the right of center; and Europa's is to the right of Ganymede's signature.

In the case of RX J1914+24, the currents which are generated are much greater than that in Jupiter since the secondary white dwarf is rotating around the primary white dwarf on a much shorter timescale and its mass is much greater than that of Jupiter's satellites. The diagram below shows how the energy is liberated on the magnetic white dwarf:
This model can explain all the observed characteristics of RX J1914+24. More detail of this model can be found in Wu et al 2002) .