Plate Nº 46 · recorded October 9, 2026
Space & AstronomyReported finding
Strong magnetic fields can push white dwarfs past the Chandrasekhar limit
Strong internal magnetic fields can let white dwarfs grow to roughly 2.4 solar masses — about 70% above the classical Chandrasekhar limit — according to new IISc simulations.
By James Calloway3 min read697 words
In brief
- Simulations show magnetized carbon-oxygen white dwarfs can reach about 2.4 solar masses, versus the 1.4-solar-mass Chandrasekhar limit for nonmagnetized models
- Some unusually bright Type Ia supernovae point to progenitor masses as high as 2.8 solar masses
- The modeled white dwarf accreted matter at 10⁻⁹ solar masses per year, starting from 1.02 solar masses
- The idea traces to a 2011 summer-student project in Banibrata Mukhopadhyay's group at IISc
- The study was published in The Astrophysical Journal Letters (2026), DOI 10.3847/2041-8213/aea97e
Strong internal magnetic fields can let white dwarfs grow to roughly 2.4 times the mass of the sun — about 70% above the well-known 1.4-solar-mass ceiling — according to new simulations from researchers at the Indian Institute of Science (IISc) in Bengaluru. The study, published in The Astrophysical Journal Letters, suggests some stars can evolve into so-called super-Chandrasekhar white dwarfs.
White dwarfs are the dense, Earth-sized remnants left behind when stars like the sun exhaust their fuel and shed their outer layers. For most of these objects, a mass limit of about 1.4 solar masses, first derived by physicist Subrahmanyan Chandrasekhar in 1930, holds firm.
What did the researchers actually find?
The team modified STARS, an evolution code developed at the University of Cambridge, to follow magnetized stars from the hydrogen-fusing main-sequence phase all the way to the white-dwarf stage. They then modeled a binary system in which the white dwarf pulls gas from a companion.
In one run, a 1.02-solar-mass carbon-oxygen white dwarf — descended from an 8-solar-mass main-sequence star — accreted matter at 10⁻⁹ solar masses per year. The magnetized version reached about 2.4 solar masses, while an otherwise identical nonmagnetized model topped out near the familiar 1.4-solar-mass ceiling.
The mechanism is mechanical. As the white dwarf packs on mass, it shrinks, and that compression amplifies its internal field. The stronger field exerts extra outward pressure, letting the star hold up under its own gravity.
"The idea started in 2011, when a summer student came to me and I gave him a problem quite casually: to check whether the Chandrasekhar limit can be violated by a magnetic field," said Banibrata Mukhopadhyay, a physics professor at IISc and the study's corresponding author.
How does this connect to real observations?
Two strands of evidence have long hinted at the possibility. Theorists predicted super-Chandrasekhar white dwarfs decades ago. Astronomers have also spotted unusually bright Type Ia supernovae whose light curves point to progenitor masses as high as 2.8 solar masses — far above the classical limit.
Type Ia supernovae matter because they explode with near-uniform peak brightness, a property that has made them a cornerstone "standardizable candle" for measuring cosmic distances. If some explosions start from heavier, magnetized progenitors, their intrinsic brightness could vary more than cosmologists assume, with knock-on effects for measurements of the universe's expansion rate.
Could stars really evolve into such objects?
That was the central puzzle, says first author Zenia Zuraiq, a Ph.D. student in IISc's Department of Physics.
"The important question was not simply whether a super-Chandrasekhar white dwarf is possible, but whether a star can actually evolve into one," Zuraiq said. "Our simulations allowed us to follow that evolutionary pathway from the main-sequence star to the white dwarf and show that under certain conditions, such a pathway is possible."
The work does not claim every white dwarf is supermassive. The mass boost depends on the strength and configuration of the internal field, and the researchers stress that their new limits hinge on the specific magnetic physics built into the model.
What about those oddly large white dwarfs?
The simulations also offer a possible explanation for a separate puzzle. Several well-studied white dwarfs appear noticeably larger than standard models predict for their measured masses. A stronger internal field, the team argues, changes the mass-to-size relationship and could account for the swollen radii.
What comes next?
The group plans to vary the magnetic-field geometry and accretion rate to see how the eventual mass limit shifts. They also want to fold in more realistic binary physics, since donor stars, mass transfer, and stellar winds can all alter the outcome.
For now, the message is modest. The 1.4-solar-mass ceiling may not be the whole story, at least not for white dwarfs that happen to be strongly magnetized. Cosmic distance measurements built on Type Ia supernovae may eventually need to account for that variation.
The study appeared in The Astrophysical Journal Letters (2026); its DOI is 10.3847/2041-8213/aea97e.
via Phys.org Space & Astronomy (Source)
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