Scientists have made a critical discovery that bridges the gap between binary star systems’ early and final stages—pairs of stars orbiting a common center of gravity. This breakthrough enhances our understanding of star formation, galaxy evolution, and the creation of most elements on the periodic table.
It could also provide insights into cosmic events like supernovae and gravitational waves, as binaries containing compact dead stars are believed to be the origin of these phenomena.
Nearly half of stars like our Sun exist in binary systems, often with one star more massive than the other. While they may appear to evolve at the same rate, more massive stars have shorter lifespans and progress through stellar stages faster.
As a star nears the end of its life, it expands significantly during the red giant phase, sometimes engulfing its companion in close binary systems—a phenomenon called the common envelope phase.
This phase remains a significant mystery in astrophysics, as scientists are still determining how the stars’ interactions during this stage influence their evolution. New research may help solve this puzzle.
When stars die, they leave behind compact remnants called white dwarfs. Discovering binary systems with a “dead” white dwarf and a “living” star, known as white dwarf-main sequence binaries, offers a unique opportunity to study the extreme phase of stellar evolution.
Lead author Steffani Grondin from the University of Toronto explains that this research marks a key step in tracing the complete life cycles of binary stars and understanding the mysterious phases of stellar evolution. Using machine learning, the researchers analyzed data from the European Space Agency’s Gaia mission, 2MASS, and Pan-STARRS1 surveys to identify new binary systems in star clusters.
While these binaries should be common, they have been difficult to find, with only two confirmed before this study. This research could increase the known count to 52 binaries across 38 clusters.
Since the stars in open star clusters are believed to have formed at the same time, discovering white dwarf-main sequence binaries in these clusters helps astronomers determine the systems’ age. This enables them to trace the binaries’ full evolution from before the common envelope phase to their current state in the post-common envelope phase.
Co-author Joshua Speagle, a professor in the David A. Dunlap Department for Astronomy & Astrophysics and Department of Statistical Sciences at U of T, said, “The use of machine learning helped us to identify clear signatures for these unique systems that we weren’t able to easily identify with just a few data points alone. It also allowed us to automate our search across hundreds of clusters, which would have been impossible if we were trying to identify these systems manually.”
Co-author Maria Drout, also a professor in the David A. Dunlap Department for Astronomy & Astrophysics at U of T, said, “It really points out how much in our universe is hiding in plain sight—still waiting to be found. While there are many examples of this type of binary system, very few have the age constraints necessary to map their evolutionary history fully. While there is plenty of work left to confirm and fully characterize these systems, these results will have implications across multiple areas of astrophysics.”
Binaries containing compact objects are key progenitors of Type Ia supernovae and mergers that generate gravitational waves detectable by instruments like LIGO. By using data from the Gemini, Keck, and Magellan Telescopes to confirm and analyze these binaries, the research team aims to create a catalog that will provide insights into elusive transient phenomena in the universe.
Journal Reference:
- Steffani M. Grondin et al., The First Catalog of Candidate White Dwarf–Main-sequence Binaries in Open Star Clusters: A New Window into Common Envelope Evolution, The Astrophysical Journal (2024). DOI: 10.3847/1538-4357/ad7500