Binary systems with living and dead stars reveal stellar secrets 

Astronomers at the University of Toronto (U of T) have identified, for the first time, pairs of white dwarf and main sequence stars within young star clusters. 

This significant finding, published in The Astrophysical Journal, opens a new window into an extreme phase of stellar evolution, offering a critical link in understanding the lifecycle of binary star systems. These insights may also shed light on cosmic events such as supernova explosions and gravitational waves.

Binary systems – where two stars orbit a shared center of gravity – are central to the universe’s evolution. 

The discovery of these rare systems could help astronomers piece together the transition between the early and final stages of binary stars, advancing our understanding of how stars and galaxies evolve and how elements are created.

Mysterious stage of stellar evolution 

Binary star systems are widespread, with about half of all stars similar to the Sun existing in such pairings. 

Typically, these stars vary in mass, which influences how they evolve. Massive stars age more rapidly, transitioning through life stages far faster than their lower-mass companions.

In the later stages of a massive star’s life, it swells dramatically during the red giant or asymptotic giant branch phases. 

In close binary systems, this expansion can engulf the smaller companion star in a shared layer of material, a phenomenon known as the common envelope phase. 

This mysterious stage plays a critical role in stellar evolution, but its details have long eluded scientists.

The role of binary star systems 

White dwarfs – the dense remnants of dead stars – provide a unique opportunity to study this phase. 

Identifying systems that pair white dwarfs with main sequence stars, known as white dwarf-main sequence binaries, offers critical clues about what happens during and after the common envelope stage.

“Binary stars play a huge role in our universe,” said lead author Steffani Grondin, a graduate student at the University of Toronto’s David A. Dunlap Department for Astronomy & Astrophysics. 

“This observational sample marks a key first step in allowing us to trace the full life cycles of binaries and will hopefully allow us to constrain the most mysterious phase of stellar evolution.”

Machine learning and star pair discovery

Despite their predicted abundance, white dwarf-main sequence binaries have been notoriously difficult to find. Before this study, only two candidates had been confirmed within star clusters. 

Using machine learning, the researchers analyzed data from three astronomical surveys: the European Space Agency’s Gaia mission, the 2MASS infrared survey, and the Pan-STARRS1 optical survey. This innovative approach uncovered 52 potential binaries across 38 star clusters.

Study co-author Joshua Speagle is a professor in U of T’s David A. Dunlap Department for Astronomy & Astrophysics and Department of Statistical Sciences. 

“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 datapoints alone,” said Speagle. 

“It also allowed us to automate our search across hundreds of clusters, a task that would have been impossible if we were trying to identify these systems manually.”

Evolutionary timeline of binary star systems

Star clusters are invaluable for studying the evolution of stars because all stars in a cluster are believed to have formed simultaneously. Finding white dwarf-main sequence binaries within these clusters allows researchers to determine the systems’ ages and trace their evolutionary paths.

“It really points out how much in our universe is hiding in plain sight – still waiting to be found,” said co-author Maria Drout, an astronomer at U of T. 

“While there are many examples of this type of binary system, very few have the age constraints necessary to fully map their evolutionary history. While there is plenty of work left to confirm and fully characterize these systems, these results will have implications across multiple areas of astrophysics.”

Implications for astrophysics and beyond

Binary systems containing compact stellar remnants are linked to some of the universe’s most dramatic events, such as Type Ia supernovae and gravitational wave-producing mergers. 

Type Ia supernovae are crucial tools for measuring cosmic distances, while gravitational waves – ripples in spacetime – are detectable by instruments like the Laser Interferometer Gravitational-Wave Observatory (LIGO).

The team plans to refine their findings using data from telescopes such as Gemini, Keck, and Magellan. 

As they confirm and measure the properties of these binaries, the researchers hope their work will provide a deeper understanding of the transient phenomena that shape our universe.

Image Credit: ALMA (ESO/NAOJ/NRAO), Olofsson et al. Acknowledgement: Robert Cumming.

—–

Like what you read? Subscribe to our newsletter for engaging articles, exclusive content, and the latest updates.

Check us out on EarthSnap, a free app brought to you by Eric Ralls and Earth.com.

—–