Every eleven years, the Sun’s magnetic field flips. Sunspots — dark, cooler regions on the Sun’s surface that mark intense magnetic activity and often trigger solar eruptions —appear at mid-latitudes and migrate toward the star’s equator in a butterfly-shape pattern before fading as the cycle resets.
While this spectacle on the star’s surface has long been visible to astronomers, where this powerful cycle begins inside the star has remained hidden — until now.
Researchers at the New Jersey Institute of Technology (NJIT) analyzed nearly three decades of solar oscillation data to trace the Sun’s interior dynamics, and have now pointed to the likely location of the star’s magnetic engine deep beneath its surface — roughly 200,000 kilometers down, about the length of stacking 16 Earths end to end.
The findings , published in Nature Scientific Reports , provide one of the clearest observational windows yet into the Sun’s magnetic engine — the solar dynamo — shedding light on hidden forces shaping space weather patterns linked to the solar cycle, not only on Earth’s nearest star but potentially on other stars across the galaxy.
“Until now, we simply hadn’t heard enough from inside the star to be certain where the Sun’s intense magnetic fields are organized,” said Krishnendu Mandal, lead author and NJIT research professor of physics . “Sunspots are the visible footprints of magnetic fields that drive space weather on the Sun’s surface, but what solar oscillation data tells us is that the actual ‘engine room’ responsible for generating them originates much deeper.”
Sounding the Sun’s Interior Across Solar Cycles
To tune into the Sun’s interior, the team bridged roughly 30 years of observations from the Michelson Doppler Imager (MDI) on board NASA’s Solar and Heliospheric Observatory (SOHO) satellite, the Helioseismic and Magnetic Imager (HMI) on board the Solar Dynamics Observatory (SDO) , and the ground-based Global Oscillation Network Group (GONG) .
The instruments have been recording sound waves generated by turbulent plasma motions within the star every 45 to 60 seconds since the mid-1990s.
By combining these observations, researchers analyzed billions of individual measurements, creating one of the longest and most detailed records of the Sun’s internal vibrations.
“Helioseismology is still a young field … reliable observations only began in the mid-1990s when GONG first came online,” Mandal explained. “Now, with nearly three 11-year solar cycles of data, we’re finally seeing clear patterns take shape that give us a window inside the star.”
Much like seismologists studying earthquakes on Earth, the researchers analyzed sound waves rippling through the Sun — measuring shifts in the waves’ travel times through the solar interior that reveal how hot plasma inside the star moves and rotates, exposing bands of faster and slower rotation beneath the surface.
The team's analysis revealed that these migrating rotation bands in the deep solar interior form a butterfly-shaped flow pattern, mirroring the sunspot migration that later emerges at the surface.
Analyzing these flow patterns through the interior pointed the team toward a critical transition layer nearly 200,000 kilometers beneath the surface — called the tachocline.
This thin boundary separates the Sun’s turbulent outer convection zone — where plasma churns and rises — from its stable radiative interior below. Across the tachocline, the Sun’s rotation changes abruptly, generating powerful shearing flows capable of powering the Sun’s magnetic fields.
“Rotation bands originating from magnetic structural changes near the Sun's tachocline can take several years to propagate to the surface,” Mandal said. “Tracking these internal changes gives us a clearer picture of how the solar cycle unfolds.”
The revealed correlation between the flow patterns across all three instruments and the degree to which they match the surface sunspot migration shows a clear connection between dynamics in the deep solar interior and solar activity on a global scale.
“For years, we suspected the tachocline was important for the solar dynamo, but now we have clear observational evidence,” Mandal said.
Clarifying where the dynamo operates could help scientists refine models used to forecast solar activity. Powerful solar eruptions — including flares and coronal mass ejections — can disrupt satellites, communications systems, navigation signals and power grids on Earth.
“While our findings do not yet enable precise predictions of future solar cycles, they highlight the importance of including the tachocline in space weather prediction models,” Mandal said. “Many current simulations account for processes only on near-surface layers, but our results show the entire convection zone, especially the tachocline, must be considered.”
The findings may also have implications beyond the Sun.
“Many stars exhibit magnetic cycles similar to the Sun's, but the high-resolution data achievable for the Sun due to its proximity to Earth is unattainable for others,” Mandal said. “Understanding the solar dynamo gives us a framework to study magnetic activity in other stars across the galaxy.”
The team at NJIT’s Center for Computational Heliophysics , led by study co-author and NJIT Distinguished Professor Alexander Kosovichev, plans to extend the team’s analysis and numerical simulations to refine their understanding of how the dynamo evolves and drives solar activity.
“There’s still much we don’t know about how the Sun’s internal magnetism evolves,” Mandal said. “With longer datasets and better observations, we hope to track these patterns across this and future solar cycles, potentially giving us better forecasts of space weather that can affect our daily life.”
The study, Helioseismic Evidence that the Solar Dynamo Originates Near the Tachocline , was supported by funding from NASA, including a grant “Consequences Of Fields and Flows in the Interior and Exterior of the Sun” from the NASA DRIVE Science Center — a collaboration of 13 U.S. universities and research centers that includes NJIT among its contributing institutions.
Helioseismic evidence that the solar dynamo originates near the tachocline
12-Jan-2026