Massive, super-hot stars are an essential part of the Universe’s history and evolution. These stars emit powerful ultraviolet energy that the Hubble Space Telescope can detect from its vantage point in Low-Earth Orbit. In December 2023, astronomers completed a groundbreaking three-year survey of these hot stars, known as the ULLYSES (Ultraviolet Legacy Library of Young Stars as Essential Standards) program. This ambitious survey collected detailed information on nearly 500 stars, providing valuable insights into the processes occurring inside these intense stellar bodies.

One of the key advantages of observing these stars in ultraviolet light is that it offers a window into their internal workings that cannot be observed from Earth due to the ozone layer blocking UV radiation. By utilizing the Hubble’s capabilities to capture high-resolution UV images, astronomers were able to gather spectra from 220 stars and combine them with archival data on an additional 275 stars. This rich dataset contains detailed information on both hot, bright, massive stars and cool, dim, low-mass stars.

Julia Roman-Duval, Lead of the ULLYSES Implementation Team at the Space Telescope Science Institute (STScI), highlighted the transformative nature of the project, stating that it would impact various fields of astrophysics, from exoplanets to the evolution of galaxies. The stellar data collected through ULLYSES has the potential to uncover new insights and open up avenues for further research in astrophysics.

Spectra obtained from the hot blue stars not only reveal their metallicity but also provide information about the powerful stellar winds they emit. By studying the iron content in stars, astronomers can determine their age relative to the Sun and gain insights into their evolutionary stage. The ULLYSES survey specifically targeted hot blue stars in low metallicity galaxies, resembling the early Universe conditions when heavier elements were scarce.

In addition to studying massive stars, ULLYSES also observed cool, red, low-mass stars known as T-Tauri stars, which are still in the process of formation. These stars emit powerful radiation during their growth phase and play a crucial role in shaping their surrounding environments. The data collected through ULLYSES will provide valuable insights into the energy release and wind dynamics of T-Tauri stars.

Overall, ULLYSES aims to create a comprehensive database of detailed spectra from young stars within the first 10 million years of their existence. This data will not only advance our understanding of stellar formation and evolution but also contribute to various areas of astronomy, including galaxy formation, supernova mechanics, and planet formation. By fostering collaboration and utilizing observations from multiple telescopes, ULLYSES represents a significant step forward in unraveling the mysteries of the Universe.

As we delve deeper into the lives of these enigmatic stars, we gain a better understanding of the intricate processes that govern the cosmos. The ULLYSES program serves as a testament to human curiosity and the relentless pursuit of knowledge about the universe we inhabit.