IISc study says strong magnetic fields could allow white dwarfs to grow beyond the Chandrasekhar limit

Researchers from the Indian Institute of Science (IISc) have discovered that strong magnetic fields could enable white dwarfs to surpass the traditional Chandrasekhar limit. A white dwarf is a small, extremely dense stellar remnant left behind after a dying star exhausts its fuel. Generally, a non-magnetized white dwarf cannot exceed 1.4 times the mass of the Sun, known as the Chandrasekhar limit.

However, simulations by the IISc team found that a magnetized carbon-oxygen white dwarf could reach up to 2.4 times the mass of the Sun, significantly exceeding the limit. The study's lead author, Zenia Zuraiq, explained that the researchers initially considered the idea in 2011 when a summer student approached him with the question of whether a magnetic field could violate the Chandrasekhar limit.

The findings support previous predictions made by theorists and are further supported by the observation of unusually luminous Type Ia supernovae, which may indicate progenitor white dwarfs with masses up to 2.8 times that of the Sun. To model this phenomenon, the team modified an existing computer code, STARS, to account for magnetic field effects and white dwarf cooling.

This allowed them to trace the evolution of magnetized stars from the main sequence – when stars generate energy by fusing hydrogen – to their eventual formation as white dwarfs. They also simulated a binary system where the white dwarf accumulates additional matter from a companion star. The simulations revealed that a weak initial magnetic field becomes more significant as the white dwarf gains mass.

As the star becomes denser and contracts under the influence of its magnetic field, the field strengthens, providing additional pressure that helps the star withstand its immense gravity and support greater mass. This discovery alters the usual relationship between a white dwarf's mass and size, introducing new mass limits depending on the specific magnetic field dynamics.