In Hoyle's model from 1944, the companion went nova with ejected material captured by the Sun and planets forming from this material. In a version a year later it was a supernova. In 1955 he proposed a similar system to Laplace, and again proposed the idea with more mathematical detail in 1960. It differs from Laplace in that a magnetic torque occurred between the disk and the Sun, which came into effect immediately; otherwise, more and more matter would have been ejected, resulting in a massive planetary system exceeding the size of the existing one and comparable to the Sun. The torque caused a magnetic coupling and acted to transfer angular momentum from the Sun to the disk. The magnetic field strength would have to have been 1 gauss. The existence of torque depended on magnetic lines of force being frozen into the disk, a consequence of a well-known magnetohydrodynamic (MHD) theorem on frozen-in lines of force. As the solar condensation temperature when the disk was ejected could not be much more than 1,000 K (730 °C; 1,340 °F), numerous refractories must have been solid, probably as fine smoke particles, which would have grown with condensation and accretion. These particles would have been swept out with the disk only if their diameter at the Earth's orbit was less than 1 meter, so as the disk moved outward, a subsidiary disk consisting of only refractories remained behind, where the terrestrial planets would form. The model agrees with the mass and composition of the planets and angular momentum distribution provided the magnetic coupling. However, it does not explain twinning, the low mass of Mars and Mercury, and the planetoid belts. Alfvén formulated the concept of frozen-in magnetic field lines.