by In December 2023, the Hubble Space Telescope completed its largest program since its launch in 1990. With this program, the telescope observed 500 individual stars over a period of three years – and scientists are now ready to dive into the Cosmic details this Easter egg.
The comprehensive Hubble Telescope survey, or ULLYSES, is known as the Ultraviolet Legacy Library of Young Stars as Essential Standards; ULLYSES operators considered Hubble to be the only active telescope capable of carrying out such a pioneering effort.
However, these ultraviolet observing feasts will last well beyond the Easter holidays, keeping researchers busy for years to come as they offer fresh insights into star formation, stellar evolution and the impact of stars on their environment.
“I believe that the ULLYSES project will be transformative, affecting the whole of astrophysics, from exoplanets to the effects of massive stars on galaxy evolution, to understanding the earliest stages of the developing universe,” Julia Roman-Duval, leader of the ULLYSES Implementation Team at the Space Telescope. The Science Institute (STScI) in Baltimore, Maryland, said in a statement. “In addition to the specific goals of the program, the constellation data can also be used in the fields of astrophysics in ways we cannot yet imagine.”
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The ULLYSES team first used Hubble to study 220 stars, then went into the space telescope’s archive to find observations of another 275 stars. The researchers also incorporate data about stars from plenty of other space telescopes and ground-based observatories.
The completed ULLYSES data set consists of stellar spectra containing information about each star’s temperature, chemical composition and the speed at which it is spinning.
Hubble and ULLYSES see red (and blue)
Of particular interest to the ULLYSES team are the big hot and massive blue stars that can be a million times brighter than our sun. These scorching stars glow strongly in ultraviolet light, meaning Hubble can easily distinguish them.
Blue giant stars live fast and die young, rapidly burning through the fuels needed for their intrinsic nuclear fusion processes and creating “metals”, the term astronomers use to describe elements heavier than hydrogen and helium. Hydrogen and helium are the main elements that stars are made of at the beginning of their lives.
Constellation spectra of blue giant stars can reveal details about the speeds of the stellar winds that escape from them. After massive stars explode in supernova explosions, these massive winds scatter the elements that formed those stars. The elements are then dispersed throughout the cosmos – therefore, understanding these winds would be a major step towards understanding the galactic distribution of the heavy elements that will be the building blocks of the next generation of stars and the planets. Those elements may be the basis for life in the universe, too.
Because of this dispersal process, each subsequent stellar generation has a greater concentration of metals than the last. Founded when most of the atoms in the universe were hydrogen and a little helium, the first generation of stars is considered “metal-poor,” and the later generations of stars, including the sun, are “metal-rich. “
ULLYSES and Hubble focused on blue stars in galaxies close to the Milky Way that appear to lack metal. These stars can therefore act as proxies for the earliest stars, helping scientists to probe the stars that existed in the infant universe and are now beyond the range where we can see in deep detail. see easily.
“The ULLYSES observations are a step forward in understanding the first stars and their winds in the universe and how they influence the evolution of their host galaxy,” said Roman-Duval.
At the other end of the color (and size) spectrum, the ULLYSES project also focused on young stars that are cooler, smaller and redder than the sun. These stars were also located closer to home, in active star-forming regions of the Milky Way.
During their formative years, as they gathered mass from the disks of gas and dust that contained them, these young, red stars created turbulence in their systems by exploding ultraviolet and high-energy X-ray light. This would affect the planet-forming disks around these stars, and it would affect whether the planets born around these stars can ever be habitable.
The Hubble observations collected for ULLYSES could help scientists better understand the processes by which these young stars accumulate material from their surroundings to accumulate the mass needed to fuel the nuclear fusion of hydrogen with helium. If that process were to begin, the young star would become a full-fledged star.
This could also reveal the effect these stars have on the disks around them, which will eventually go on to form planets. Therefore, studying the survey could help scientists better understand the systems most suitable for the search for life.
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“ULLYSES was originally conceived as an observing program using Hubble’s sensitive spectrographs. However, the program has greatly contributed to coordinated and complementary community-led observations with other ground-based and space-based observatories,” said Roman-Duval. “Such broad coverage allows astronomers to explore the lives of stars in unprecedented detail and paint a more comprehensive picture of the properties of these stars and how they affect their environment.”
Even before ULLYSES data offers new insights into the lives of stars and their environments, this survey shows that Hubble is still delivering cutting-edge science even after more than two decades of cosmic observations.
