Scientists Discover Magnetic Fossil Fields in Dead Stars

Ancient Magnetism Survives Stellar Death

Scientists have uncovered compelling evidence that magnetic fields born in a star's youth can survive billions of years, persisting through every stage of stellar evolution to emerge as "fossil fields" on the surfaces of white dwarf remnants. This groundbreaking discovery links magnetic fields that form early in a star's life to the magnetism observed on long-dead stellar remnants, suggesting these ancient forces endure throughout a star's entire existence.

The research, led by astrophysicists at the Institute of Science and Technology Austria, represents the first time scientists have connected magnetic fields observed at the surfaces of white dwarfs to magnetism detected deep within red giants—the dying stars that eventually become those compact remnants. For the first time, they connect the evidence of magnetic fields reaching the surface of older white dwarfs to recent findings of magnetism in the cores of red giants—the dying progenitors of those remnants.

Starquakes Reveal Stellar Secrets

The breakthrough came through asteroseismology, the study of stellar oscillations or "starquakes" that ripple through a star's surface much like earthquakes reveal Earth's interior structure. Similar to earthquakes, starquakes are natural phenomena that allow scientists to obtain measurements of the insides of stars. These measurements have revealed that magnetic fields exist at the cores of red giants, while white dwarfs seem to have magnetic fields at their surfaces.

The team's theoretical models show that these magnetic fields don't concentrate at a star's core like a bar magnet, but instead form hollow, shell-like structures resembling a basketball's surface. Rather than being centered at one point, their simulations suggest that magnetic fields can form shell‑like structures—resembling the surface of a basketball—where the field is strongest near the shell rather than at the core. These structures persist through the red giant phase and eventual collapse into a white dwarf, with the ancient fields migrating outward over billions of years to appear at the surface.

Implications for Our Sun's Future

In around 5 billion years, the sun will have exhausted the hydrogen in its core, no longer able to perform its nuclear fusion process that converts this element into helium. This research could fundamentally change our understanding of what happens next. If magnetic fields can indeed extend a star's lifespan by mixing hydrogen from outer layers into the core, "If the Sun can somehow bring hydrogen from its outer layers into its core, it would be able to live longer. One way to do this would be through strong magnetic fields," explains lead researcher Lukas Einramhof.

However, scientists remain largely in the dark about our own star's magnetic interior. "We still don't know whether the Sun's core is magnetic. Even though it's our own star, we're practically blind to what happens at its center," Einramhof notes. "Current predictions assume that the Sun's core is not magnetic. But if it turns out to be, this information would change everything we know and all the models we've based our work on."

A New Chapter in Stellar Physics

The fossil field theory helps explain a puzzling observation: "Generally, more of the older white dwarfs tend to be more magnetic than younger white dwarfs." This pattern makes sense if magnetic fields are ancient features that gradually emerge at the surface as white dwarfs cool and evolve over cosmic time scales.

The research suggests that magnetism may be far more common in stars than previously thought. "Given how little we know at this stage, our work suggests that stars are most likely all magnetic. But we can't always detect this magnetism," Einramhof concludes. As astronomers develop better techniques to probe stellar interiors, these ancient magnetic fossils may unlock new secrets about how stars live, evolve, and ultimately die across the universe.