The Gaia Satellite, White Dwarf Stars, and the Age of the Galaxy

Embry-Riddle Aeronautical University, Daytona Beach FL

Investigators

Abstract

The Milky Way is pictured as containing four major populations of stars known as the thin disk, thick disk, bulge, and halo. All these populations formed more than 8 billion years ago and must be younger than about 13.7 billion years old, the age of the Universe. For perspective, the Sun is about 4.5 billion years old. Yet, the ages of each of these Galactic populations is uncertain to one or two billion years. Without better knowledge of the ages of these populations, astronomers cannot answer fundamental questions about the formation of the Galaxy. To progress on these questions, astronomers need to improve how they determine the ages of stars. The investigators developed a new technique that more precisely determines the ages of stars than any prior technique. This technique takes advantage of data from the Gaia satellite and advanced Bayesian statistics. The project will train physics, mathematics, and software engineering students at Embry Riddle Aeronautical University in modern statistical and analysis methods. The students will gain valuable experience working with researchers and students abroad. The team includes the statistics group at Imperial College in London, England, and the Gaia research group at the Max Planck Institute in Heidelberg, Germany. The project is committed to including the full participation of women and underrepresented minorities. Therefore, the project will improve Science, Technology, Engineering, and Mathematics (STEM) education in the United States. It will also contribute to a diverse and globally competitive STEM workforce. Many types of stars are presently used as age proxies, yet among them white dwarf stars hold the most promise. A white dwarf's luminosity directly encodes its age, but this relies on accurately measuring its distance. The Gaia satellite is currently measuring the most accurate and precise trigonometric parallax distances ever obtained. Among the ~1.7 billion stars that Gaia is observing, there will be ~15,000 white dwarfs within 100 pc with typical distance uncertainties < 1%. This compares to only two white dwarfs with distances presently known this accurately. The proposers will combine these Gaia data with optical and near-infrared photometry from ground-based surveys. They will analyze these data with their well-tested modeling technique, which relies on Bayesian statistics and state-of-the-art model ingredients. These unprecedented data and new modeling technique will allow the proposers to (1) derive ages for thousands of white dwarfs with typical age precisions of 1 to 5%, and then subsequently determine (2) the star formation history in the disk, (3) the onset and cessation of star formation in the thick disk, and (4) the mean age and age dispersion of the halo.