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New Horizons Unveils First Lyman-Alpha Map of Our Galactic Neighborhood
The NASA New Horizons mission has successfully generated the first comprehensive map of Lyman-alpha emissions emanating from our galaxy, marking a significant milestone in our understanding of the cosmic environment surrounding the solar system. This groundbreaking achievement is detailed in a recent study produced by the Southwest Research Institute (SwRI)-led New Horizons team.
The newly published research, titled “The Lyman-alpha Sky as Observed by New Horizons at 57 AU,” appears in The Astronomical Journal. Lead investigator Dr. Randy Gladstone emphasizes the significance of this research for understanding the structures and dynamics of nearby galaxies. “Understanding the Lyman-alpha background helps shed light on nearby galactic structures and processes,” he stated, adding that hot interstellar gas bubbles might signify regions of elevated hydrogen emissions at Lyman-alpha wavelengths.
Lyman-alpha represents a particular ultraviolet wavelength produced by hydrogen atoms. Astronomers utilize this wavelength extensively to study distant stars, galaxies, and the interstellar medium since it offers insights into their composition, thermal states, and movement.
During its journey to Pluto, New Horizons gathered fundamental data regarding Lyman-alpha emissions via the Alice instrument, an ultraviolet spectrograph developed by SwRI. This device effectively breaks down light into its various spectral components, particularly focusing on far-ultraviolet wavelengths.
Upon completing its primary mission at Pluto, the New Horizons team leveraged Alice to conduct broader explorations of Lyman-alpha emissions as the spacecraft ventured deeper into the solar system. A comprehensive series of observations in 2023 facilitated the mapping of approximately 83% of the sky.
To differentiate emissions specific to the galaxy, the team modeled solar Lyman-alpha emissions and systematically subtracted this data from their findings. The results revealed a uniform brightness in the Lyman-alpha background, estimated to be ten times greater than previous calculations suggested.
“These results indicate that the emission and scattering of Lyman-alpha photons arise from hydrogen atoms in a hot gas bubble enveloping our solar system and neighboring stars, likely formed by supernovae millions of years ago,” noted Gladstone.
Interestingly, the study found no substantial evidence supporting the existence of a hydrogen wall surrounding the sun’s heliosphere that would significantly contribute to Lyman-alpha emissions. Prior theories proposed that interstellar hydrogen would accumulate at the boundary of our heliosphere, the area dominated by solar wind interacting with the interstellar medium. However, New Horizons data did not validate these assumptions.
“These observations are a landmark achievement, offering the first clear perspective of the sky surrounding our solar system in Lyman-alpha wavelengths,” remarked Dr. Alan Stern, Principal Investigator for the New Horizons project. He emphasized that these findings not only reveal new attributes of the galactic sky but also challenge previous scientific ideas, establishing a robust base for future studies.
More information: G. Randall Gladstone et al, The Lyα Sky as Observed by New Horizons at 57 AU, The Astronomical Journal (2025). DOI: 10.3847/1538-3881/adc000
Citation: New Horizons observations lead to first Lyman-alpha map from the galaxy (2025, April 28) retrieved 28 April 2025 from https://phys.org/news/2025-04-horizons-lyman-alpha-galaxy.html
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