Hubble’s Ultraviolet Legacy Library of Young Stars as Essential Standards
Introducing Hubble’s ULLYSES Program
Detailing the lives of young stars
For centuries, astronomers have studied the stars, gathering information about their precise positions and compositions to learn how they form. But it wasn’t until telescopes were launched into space that we could begin to capture some of the most important information – which is delivered by ultraviolet light.
Ultraviolet emissions highlight part of the hottest material and the most energetic processes of stars that recently formed or are still forming. Only the Hubble Space Telescope is currently capable of making high-resolution ultraviolet light observations, which is why it has embarked on an extensive three-year program, known as Hubble’s Ultraviolet Legacy Library of Young Stars as Essential Standards (ULLYSES), to observe a set of high- and low-mass young stars.
Hubble will build this dataset not with images, but by gathering spectra, which spread light into its component wavelengths and reveal details about each star’s size, temperature, speed, distance and composition. These data will help astronomers learn how stars form and what their compositions are just after forming.
With these data, researchers will also be able to trace material as it follows magnetic fields onto young stars, measure the strength and makeup of their stellar winds, and learn how the stars impact their environments as or soon after they form.
Hubble’s ULLYSES program will observe the ultraviolet light stars emit—and spread that light into its component wavelengths, which are known as spectra. This graph, which shows two spectra, maps how much far-ultraviolet light the two stars are emitting through the gas in their surrounding galaxies. The star in the dwarf galaxy Sextans A, represented in purple, has emitted light, but there isn’t much gas nearby absorbing it. In contrast, the star in the Large Magellanic Cloud, represented in teal, shows that there is sulfur blocking some of its light. By analyzing the elements between us and the stars, researchers can learn about the conditions and history of the gas and dust surrounding stars in distant galaxies. Download this image.
These spectra reflect the intense winds of massive stars in N11 in the Large Magellanic Cloud, set off in teal, and NGC 346 in the Small Magellanic Cloud, set off in purple. By tracing the width of the dips shown on the graph, we can measure the wind speeds. Narrower vertical dips reflect slower winds and wider vertical dips reflect faster winds. The star represented by the purple line is emitting a slower wind, while the star represented by the teal line has intense, faster winds, which means it is losing mass at a faster speed. Download this image.
These spectra show the presence of iron in two stars. The star in Sextans A, represented in purple, doesn’t contain much iron, which implies that it may have formed from elements that made up the early universe, which contained a higher percentage of hydrogen and helium. The star in the Large Magellanic Cloud, represented in teal, has dips that reflect the presence of iron. This star is made from the elements expelled into its environment from previous generations of stars. The amounts of heavier elements, such as iron, can affect the life of the star and the strength of its winds. Download this image.
Examining the Lives of Young Stars in Unprecedented Detail
Hubble’s ULLYSES program will observe approximately 200 stars in 10 star-forming regions in our Milky Way galaxy and in nearby low-metallicity dwarf galaxies. Its targets are a mix of high- and low-mass young stars.
The young high-mass stars are extremely active. These stars inject an amazing amount of energy into their surrounding environments through ultraviolet radiation and stellar winds, which impact local star formation. Their activity is matched by how long they take to form: Young high-mass stars form rapidly over thousands of years. Hubble’s observations will help researchers learn more about how their makeup, specifically their metallicities, control the strengths of the winds they emit as well as how easily these stars can eject matter.
In contrast, young low-mass stars can take a few million years to form. Hubble will observe several of these young low-mass stars repeatedly, tracing how they gather material and emit UV radiation, and change over short timescales. The observatory’s ultraviolet spectra will show where the stars are most actively collecting this new material and how they are impacting their immediate environments. For example: Why do these young low-mass stars launch opposing jets? How do those jets inject energy into their environments?
Stimulating Research for Decades to Come
Hubble’s ULLYSES program was built by and for the research community, and its data will be quickly released following each set of observations. The goal is for researchers around the world to download and analyze them, publishing new breakthroughs about how young stars form.
Astronomers may also go on to compare this ultraviolet data with complementary data – in radio and infrared to visible and X-rays – from a range of observatories that are both on the ground and in space. The program’s overarching goal is to provide a definitive data set on the first 10 million years of stellar evolution and help researchers understand the complexity of ultraviolet spectra.
The program, which will ultimately be a library that researchers continue to reference for decades to come, will also support the exploration of a range of research topics. More fully understanding the formation and lives of young stars has connections to many other areas in astronomy, including galaxy formation and evolution, the mechanics and mass loss of supernovas, how stars’ environments impact planet formation, and how their emissions may play a role in the makeup of the interstellar medium. Hubble’s ULLYSES data applications are practically endless – and will influence our understanding of the universe in ways we cannot yet predict.
