For decades, scientists have grappled with the challenge of accurately estimating the helium abundance in the Sun’s photosphere, the layer that emits the sunlight we observe. A recent study conducted by a team of researchers from the Indian Institute of Astrophysics (IIA) has made significant progress in this area, providing the first direct measurement of helium in the Sun’s outer layer. This finding is not just a pivotal advancement in astrophysical research; it has broader implications for our understanding of stars, their evolution, and the universe.
Traditionally, astronomers estimated the helium abundance in the photosphere indirectly. They relied on observations from hotter stars and conducted seismology studies of the Sun’s interior. An implicit assumption held that helium abundance in sun-like stars was about one-tenth that of hydrogen. However, these methods have inherent limitations due to the lack of observable helium spectral lines in the photosphere.
As a light element, helium does not easily produce distinctive absorption lines that could be measured directly in the sunlight. Instead, scientists typically observed absorption lines from heavier elements and extrapolated helium levels from those findings. This dependence on indirect methods has made it difficult to ascertain accurate measurements.
The IIA study stands out for its innovative approach. Published in the Astrophysical Journal, the research team utilized high-resolution solar spectrum observations for their analysis. By modelling the spectral lines of neutral magnesium and carbon, as well as lines from hydrogenated molecules of these elements, the researchers were able to derive a more reliable estimate of helium abundance.
First author Satyajeet Moharana, currently a PhD scholar at the Korea Astronomy and Space Science Institute (KASI), emphasized the importance of the novel technique developed by the team. “This method allows for a consistent measurement of the relative abundance of helium in the photosphere, overcoming the limitations of previous estimates,” he stated.
The accurate measurement of helium abundance in the Sun has significant implications for various fields of astrophysics. For one, it can refine models of solar opacity, affecting our understanding of the Sun’s structure and temperature distribution. This knowledge is crucial for deciphering stellar behaviour, the formation of stars, and the evolution of galaxies.
Moreover, understanding the chemical composition of the Sun provides vital context for studying other stars. Since the Sun is considered a benchmark for solar-like stars, improving our helium abundance estimates helps astronomers better comprehend the lifecycle of stars throughout the universe.
-Raja Aditya
