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

When a dying star runs out of fuel and sheds its outer layers, its remaining core can become an extremely dense remnant of a star about the size of Earth called a “white dwarf.” | Photo credit: K. MURALI KUMAR

Simulations by researchers at the Indian Institute of Science (IISc) and their collaborators show that strong internal magnetic fields could allow some white dwarfs to grow to masses significantly higher than the Chandrasekhar limit.

When a dying star runs out of fuel and sheds its outer layers, its remaining core can become an extremely dense remnant of a star about the size of Earth, called a “white dwarf.” For a white dwarf that is not strongly rotating or unmagnetized, there is a well-known upper mass limit of about 1.4 times the mass of the Sun, known as the “Chandrasekhar limit”.

In one of their simulations, the researchers found that a magnetized carbon-oxygen white dwarf could reach about 2.4 times the mass of the Sun—well above the limit.

“The idea started in 2011 when a summer student came to me and I casually gave him a problem: to check whether the Chandrasekhar limit can be violated by a magnetic field,” said Banibrata Mukhopadhyay, a professor in the Department of Physics and corresponding author of the study published in The Astrophysical Journal Letters.

Predicted for decades

IISc said theorists had been predicting the possibility of such “super-Chandrasekhar” white dwarfs for decades. Observations of unusually bright Type Ia supernovae have added support, suggesting the possibility that progenitor white dwarfs have a mass and mass limit of up to 2.8 times the mass of the Sun.

“The important question was not only whether a super-Chandrasekhar white dwarf is possible, but whether a star can actually evolve. Our simulations allowed us to trace this evolutionary path from a main-sequence star to a white dwarf and show that under certain conditions such a path is possible,” said Zenia Zuraiq, first author of the study and a PhD student in the Department of Physics.

As they watched

To track this evolution, the team adapted STARS, a computer code developed at the University of Cambridge to model how stars evolve. They incorporated the effects of the white dwarf’s magnetic field and cooling, allowing them to follow magnetized stars from the main sequence – the long phase when stars generate energy by hydrogen fusion – to their later evolution into white dwarfs. They then modeled a binary system in which the white dwarf gains additional mass from the companion star.

The simulations showed that the magnetic field, which is initially too weak, can become increasingly important as the white dwarf gains mass. As mass accumulates, the white dwarf becomes denser and contracts, strengthening its magnetic field. The stronger field provides additional pressure inside the star, helping it resist its own immense gravity and supporting more mass. This changes the usual relationship between white dwarf mass and size, with a new mass limit(s) depending on the exact physics of magnetic fields.

Published – 9 Oct 2026 20:21 IST