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Aman in graduation attire.
Aman in graduation attire.
Aman on top of a mountain.
Aman on top of a mountain.
Aman Priyadarshi Kumar, a recent University of Colorado Boulder alum, graduated Magna Cum Laude with degrees in Astrophysics and Physics. His distinguished undergraduate thesis on magnetic structures on the Sun earned him the “Amazing Grads 2024” accolade and a platform to give the student address at the graduation ceremony, reflecting on his journey as an international student from Nashik, India. Currently pursuing a PhD in Astronomy at NMSU, Aman’s research spans solar physics, helioseismology, and magnetohydrodynamics. His work at CU Boulder’s LASP and participation in NASA’s L’SPACE Academy underscore his academic dedication. Outside academia, Aman is passionate about hiking, camping, rock climbing, basketball, cricket, and chess. The picture on the left, in fact, features Aman atop Mount Elbert, the highest peak in Colorado, celebrating one of his many hiking achievements. This Astrobites post dives into his undergraduate thesis research.
A graph of time vs. total solar irradiance that peaks every 11 years, demonstrating the solar cycle.
Figure 1: Variations in Total Solar Irradiance, 1850-2012. This graph, based on data from the GISS CMIP5 TSI model and modifications by Lean (2015), illustrates the periodic fluctuations in solar irradiance over the last 162 years, highlighting the cyclical nature of solar activity tied to the 11-year sunspot cycle. Image credit: NASA/Goddard Space Flight Center, https://data.giss.nasa.gov/modelforce/solar.irradiance/
The Sun, often considered a constant source of energy, exhibits subtle yet significant variations in its radiative output, particularly over the course of its 11-year activity cycle as is shown in Figure 1.
These variations, driven by dynamic solar activities such as sunspots and faculae, are not merely of academic interest but have practical implications for space weather forecasting, climate studies, and the protection of Earth’s technological infrastructure. At the heart of these phenomena is the solar dynamo process, where conductive plasma movements inside the Sun generate and modify magnetic fields. Figure 2 demonstrates how the Sun’s differential rotation—faster at the equator than at the poles—complicates this process, stretching and twisting magnetic field lines.
Three diagrams of the Sun's magnetic field lines, which warp around the Sun as it rotates.
Figure 2: This sequence of diagrams illustrates the solar dynamo process, where differential rotation across the Sun’s latitude causes magnetic field lines to stretch, twist, and eventually loop outward, exemplifying the complex life cycle of solar magnetic fields. Image credit: Astronomy – UCF Pressbooks,https://pressbooks.online.ucf.edu/astronomybc/chapter/15-2-the-solar-cycle/, licensed underCC BY-SA 4.0
An image of the Sun with black sunspots, and white groups of faculae.
Figure 3: While the sunspots tend to make the Sun look darker, the faculae make it look brighter. Image credit: NASA/Goddard Scientific Visualization Studio, https://svs.gsfc.nasa.gov/2656
This interaction, coupled with convection currents and turbulent motions from the Sun’s nuclear fusion core, not only amplifies these fields but also affects solar brightness. Sunspots and faculae are both magnetic areas, but the magnetic fields in faculae are concentrated in much smaller bundles than in sunspots.
Interestingly, during peak sunspot cycles, the brighter faculae tend to dominate over darker sunspots, leading to a slight increase in solar brightness (about 0.1%). Understanding how the size and strength of these magnetic structures, particularly faculae, influence solar irradiance is crucial for making sense of the Sun’s impact on our planet.
Methodology
This research leveraged two advanced observational platforms: the Sunrise Balloon-Borne Solar Observatory and the Precision Solar Photometric Telescope (PSPT). Operating at altitudes between 35-40 km above Earth’s atmosphere, Sunrise employs a one-meter aperture telescope, achieving a high resolution of 0.055 arcsecond/pixel. This allows for precise measurements using instruments like the Sunrise Filter Imager (SuFI) and the Imaging Magnetograph eXperiment (IMaX), which captures images and magnetic field data of the Sun’s surface.
An image of a sunspot, overlayed with contours representing magnetic field intensity.
Figure 4: Red contours created using our formula highlight the sunspot, showing that our method effectively traces the sunspot’s magnetic field. Image credit: Aman Priyadarshi Kumar
Simultaneously, the PSPT located at the Mauna Loa Solar Observatory in Hawaii, captures full-disk solar images at ~1 arcsecond/pixel in three key wavelength bands: blue and red continuum, and Ca II K. The Ca II K line, which is particularly sensitive to magnetic field strengths, is crucial as PSPT does not possess a magnetograph. By integrating these observations with a rigorous empirical method to convert Ca II K-line emission data into actual magnetic field strengths, we established a robust basis for understanding solar magnetic dynamics. Figure 4 demonstrates that the magnetic fields found correspond with the location of sunspots, highlighting that our method effectively traces the sunspot’s magnetic field.
Analysis
In analyzing the solar magnetic fields, a critical threshold was established to identify where the magnetic fields begin to concentrate significantly. This threshold, shown in Figure 5, set at an unsigned vertical magnetic flux greater than 20 Gauss, pinpointed pixels where magnetic fields start accumulating in the flow lanes, leading to the formation of magnetic structures. The analysis utilized 42 timesteps of Sunrise 1 data, taken 33 seconds apart, with a spatial sampling of 1 arcsecond per pixel, approximately 280 km on the solar surface.
A graph of magnetic flux vs. intensity, showing that the flux threshold of 20 Gauss corresponds with the minimum mean intensity.
Figure 5: Threshold was chosen based on the location of the minimum mean intensity, and represents the pixels where the magnetic field has begun to concentrate in the flow lanes to form magnetic structures (as inferred from the increase in mean intensity of pixels with Bz larger than ~20 Gauss). Image credit: Aman Priyadarshi Kumar
Using this, we constructed a plot showing the average intensity and mean magnetic field magnitude of these structures as a function of their width, shown in Figure 6. This visual representation helped highlight how larger solar features, which are often areas of intense magnetic activity, correspond to stronger magnetic fields.
Figure 6: These plots show the average intensity and the mean magnetic field magnitude of magnetic structures as a function of width for Sunrise 1 data (left) and PSPT data (right). Image credit: Aman Priyadarshi Kumar
The analysis was complemented by a series of 28 PSPT images, shown in Figure 6, which required alignment and correction for limb-darkening to ensure accurate comparative analysis across observational platforms.
Results
Our observations from the Sunrise 1 and Precision Solar Photometric Telescope (PSPT) revealed a direct relationship between the size of solar structures and their magnetic field strength. However, this study did not establish a definitive quantitative correlation between the magnetic field strength and the brightness of these solar structures. While magnetic structures typically appear visually brighter on the Sun’s surface, the opportunity remains to further study and quantify the exact relationship between their magnetic field strength and intensity.
Astrobite edited by: Annelia Anderson
Featured image credit: NASA/Goddard Space Flight Center Scientific Visualization Studio, https://svs.gsfc.nasa.gov/4892