This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: The more astronomers learn about the universe's earliest galaxies, the stranger they seem. Many of their surprising properties may be explained by differences between their massive stars and those in galaxies like our own Milky Way.
A new University of Utah-led survey with the Hubble Space Telescope is shedding light on the stellar astrophysics operating in early galaxies. The survey, called the Treasury of Extremely Metal-Poor O Stars (TEMPOS), uses ultraviolet (UV) observations from Hubble's Cosmic Origins Spectrograph (COS) to study massive stars in nearby galaxies that are the best available analogs of stars in the early universe. The unprecedentedly large dataset from TEMPOS could help astronomers build better models of massive stars to understand how they shaped galaxies when the universe was young.
Such models are essential to interpret observations of early galaxies now coming from the James Webb Space Telescope, which launched in 2021. "Webb opened up a whole bunch of new questions about the evolution of these early galaxies—they're weird," said Grace Telford, assistant professor in the Department of Physics & Astronomy at the University of Utah and lead author of the study. "That's the scientific motivation behind the TEMPOS program: to help understand what is going on in these early galaxies." The survey is published in The Astrophysical Journal Supplement Series.
Massive stars—those with masses more than 10 times greater than the sun—are rare but powerful engines of galactic change. They produce intense radiation, shed material through stellar winds and eventually explode as supernovae. "They burn very hot, bright and fast and they end their short lives as supernova explosions that deposit a lot of energy and material into the surrounding gas," Telford said.
"They govern the evolution of their host galaxies by heating and essentially regulating the gas that's then available to cool and form into new stars." Astronomers use the term metallicity to describe the abundance of elements heavier than hydrogen and helium. The universe's earliest galaxies contained far fewer heavy elements than galaxies like the Milky Way do today. The massive stars forming in those galaxies likely also had different physical properties.
"Massive stars at low metallicity are particularly important for building accurate models of early galaxies," Telford said. "And we can't just study how metal-rich massive stars in the Milky Way behave to interpret those observations." Instead, TEMPOS looked to nearby, low-mass dwarf galaxies, which have low metallicities more typical of galaxies near the dawn of the universe. TEMPOS surveyed 29 massive stars across six local dwarf galaxies that all have metallicities below one-fifth that of the sun.
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