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The NASA New Horizons spacecraft has achieved a significant milestone by creating the first map of Lyman-alpha emissions from the galaxy, providing unprecedented insights into the ultraviolet landscape surrounding our solar system. This groundbreaking research is presented in a recent study by the New Horizons team, led by the Southwest Research Institute (SwRI).
Dr. Randy Gladstone, the lead investigator and primary author of the study, remarked, “Gaining a better understanding of the Lyman-alpha background illuminates the structures and processes of nearby galaxies. Our findings suggest that the hot interstellar gas bubbles, like the one our solar system resides in, may represent areas of heightened hydrogen gas emissions detected at the Lyman-alpha wavelength.”
Lyman-alpha is a specific ultraviolet wavelength emitted and scattered by hydrogen atoms. It holds particular significance for astronomers as it aids in examining distant celestial objects, allowing them to probe the composition, temperature, and motion of stars, galaxies, and the interstellar medium.
During its voyage to Pluto, New Horizons gathered essential baseline data on Lyman-alpha emissions utilizing the Alice instrument, a specialized ultraviolet spectrograph developed by SwRI. A spectrograph is designed to dissect light into its constituent colors, and Alice operates within the far-ultraviolet wavelength range.
Following the completion of its primary mission objectives at Pluto, scientists redirected Alice to conduct more expansive and frequent surveys of Lyman-alpha emissions as New Horizons journeyed further away from the Sun. This ambitious effort included comprehensive scans in 2023 that mapped approximately 83% of the observable sky.
To accurately identify emissions from the galaxy, the New Horizons team created models of scattered solar Lyman-alpha emissions, subtracting this data from what the spectrograph recorded. Their findings revealed a nearly uniform background brightness of Lyman-alpha emissions that is about ten times stronger than previous expectations.
According to Gladstone, “These findings indicate that Lyman-alpha photons are emitted and scattered by hydrogen atoms present in a hot bubble surrounding our solar system, a structure formed by supernova events millions of years ago.”
The study also determined that there was no significant evidence supporting the existence of a hydrogen wall hypothesized to encircle the Sun’s heliosphere, contributing to Lyman-alpha emissions. Previous theories suggested that interstellar hydrogen atoms could compile at the edge of the heliosphere, a vast area influenced by solar wind interacting with the interstellar medium. However, the data from New Horizons did not support this notion as a crucial source of Lyman-alpha emissions.
Co-author and New Horizons Principal Investigator Dr. Alan Stern stated, “These observations are groundbreaking, offering a clear view of the surrounding sky at these wavelengths. Not only do they unveil new characteristics of that sky, but they also challenge earlier theories that the Alice New Horizons data does not endorse. This Lyman-alpha map establishes a robust base for future studies aimed at uncovering even more.”
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