The GALAH Fourth Data Release Provides Vital Data on One Million Stars in the Milky Way.

For the past ten years, Australia’s ARC Centre of Excellence in All Sky Astrophysics in 3 Dimensions (ASTRO 3D) has been investigating star formation, chemical enrichment, migration, and mergers in the Milky Way with the Anglo-Australian Telescope (AAT). Their work is part of the GALactic Archaeology with HERMES (GALAH) project, an international collaboration of more than 100 scientists from institutes and universities worldwide. These observations have led to the highest spectral resolution multi-dimensional datasets for over a million stars in the Milky Way.

Previous GALAH data releases have led to many significant discoveries about the evolution of the Milky Way, the existence of exoplanets, hidden star clusters, and many more. In the fourth data release (DR4), the GALAH team released the chemical fingerprints (spectra) for almost 1 million stars. This data is the pinnacle of the 10-year project and was released during the 50th anniversary celebration of the AAT. According to the study that accompanied the release, the data will inform decades of research into the formation and evolution of our galaxy.

The study was led by Sven Buder, a research fellow at ASTRO 3D and the Australian National University (ANU). He was joined by an international team of researchers from ANU’s Research School of Astronomy and Astrophysics, ASTRO 3D, ACCESS-NRI, the UNSW Data Science Hub, the Sydney Institute for Astronomy, Astrophysics and Space Technologies Research Centre, Space Telescope Science Institute (STScI), the Stellar Astrophysics Centre, the International Space Science Institute, and multiple universities. The paper describing the data release recently appeared in the Publications of the Astronomical Society of Australia.

The GALAH survey relies on the High Efficiency and Resolution Multi-Element Spectrograph (HERMES) working in conjunction with the 2-degree field (2dF) positioner. Both instruments are part of the Anglo-Australian Telescope (AAT) located at the Siding Spring Observatory in Coonabarabran, New South Wales. The 2dF positioner places a fiber at a star’s location in order for the light to pass to the HERMES instrument, which obtains detailed spectra of 392 objects at a time over two degrees of the sky. As Dr. Buder explained in a recent Science in Public news release:

“Our work is focused on collecting as much quality data as we can,” said ASTRO 3D’s Sven Buder, a research fellow at the Australian National University. GALAH has shown us which chemical elements make up the stars of the Milky Way. This dataset now helps further our ability to accurately age the stars in our neighborhood and understand where they came from. This data becomes a powerful tool for astronomers to test new theories and make new scientific discoveries about the Universe.”

The project scientists also rely on data from the Gaia, Kepler, and CoRoT missions, which have gathered optical data on countless stars in our galaxy. The GALAH project aims to determine the ages of these stars via their chemical signatures to get a clearer picture of the assembly of the Milky Way. This will allow astronomers to estimate a timeline of the Galaxy’s chemical and dynamical evolution and to investigate changes in the rate of star formation rate over time.

“We have measured the elements within these stars, like carbon, nitrogen, oxygen, as well as heavy elements found in our smartphones and electric vehicles,” added Dr. Buder. “This data will help us figure out how these elements are produced in stars, which is fundamental to explaining the origins of the building blocks of life.”

The spectral data consists of the visible spectrum with overlapping barcodes that indicate at which wavelengths light is being absorbed. These are the “chemical fingerprints” of the star, revealing their overall composition. This data will also help astronomers understand how the elements were formed and distributed throughout the Universe, offering hints about cosmic evolution. As if that wasn’t enough, the spectra can also be used for potentially detecting signatures of planetary systems.

In the past, GALAH data has shown stars that may have consumed planets as the Milky Way developed. Said co-author Professor Daniel Zucker of Macquarie University:

“The GALAH survey has detected signs that some stars may have ‘eaten’ planets that were orbiting them. This can be observed by looking at the chemical composition of the star, as the elements from the consumed planet would show up as markers in the star’s spectrum.”

The GALAH datasets have had a profound impact on the global astronomical community and led to 290 scientific studies to date. The previous data release (DR3) paper covered 300,000 stars and became the most cited work of the year for the journal responsible. With data on almost 1,000,000 stars, the scientific impact of this latest release is expected to be tremendous. The GALAH dataset is also expected to play a vital role in training the next generation of machine-learning tools, which are increasingly important to astronomy.

“We are really looking towards an incredibly exciting period over the next few years where all of these discoveries about what’s happening in our Universe are going to flow from the data that we’ve collected right here in Australia using Australian telescopes and building on Australian research,” said Associate Professor Sarah Martell of UNSW, a key member of the project. Professor Emma Ryan-Weber, the Director of ASTRO 3D, added that the GALAH project is directly aligned with ASTRO 3D’s mission:

“It helps us understand how galaxies build mass over time. The chemical information the research team has gathered is like stellar DNA – we can use it to tell where each star has come from. We can also determine their ages and movements and gain a deeper understanding of how the Milky Way and other galaxies formed and have evolved. What’s more, as the ASTRO 3D mission comes to a close, the GALAH project will leave a lasting legacy of Australian science informing astronomical discoveries about the Universe’s origins and development for decades to come.”

The DR4 release can be found here, while the entire list of GALAH datasets can be found here.

Further Reading: Science in Public