Maude Gull and her team discovered an extraordinary star system in the nearby Wolf-Lundmark-Melotte (WLM) galaxy. Using archival data from both the Hubble Space Telescope (HST) and the James Webb Space Telescope (JWST), they identified a candidate for a "contact binary," a system where two stars orbit so closely that they touch. This finding is significant because it represents the lowest metallicity contact binary discovered to date, offering insight into how stars evolve and merge in environments with very little metal content.

What are Contact Binaries?

A contact binary is a system where two stars are so close that they share a common atmosphere, eventually leading to a merger. This system, named WLM-CB1, is composed of two massive stars, with one being about 16 times the mass of the Sun, and the other around 7 times that size. Contact binaries are crucial for understanding the evolution of massive stars, which often end in phenomena like supernovae or the formation of black holes.

Observing the Binary in WLM

WLM-CB1 was discovered through time series data collected by Hubble and Webb, initially aimed at studying different types of variable stars. The researchers measured changes in brightness over time, suggesting that these stars eclipse each other as they orbit. By using sophisticated software, they modeled the system's light curve and estimated the temperatures and masses of the stars. The system has a relatively short orbital period of about 1.1 days, meaning the stars complete a full orbit around each other very quickly.

Importance of Low Metallicity

WLM is a metal-poor galaxy, meaning its stars formed with only a small fraction of the heavier elements found in galaxies like our Milky Way. Metallicity is an important factor in stellar evolution because it affects how stars lose mass and energy. The stars in WLM-CB1 are low in metals, which gives astronomers a unique opportunity to study how these stars behave differently from their higher-metallicity counterparts.

Modeling the Future of WLM-CB1

The team used simulations to predict the future of WLM-CB1. They suggest the stars are currently in a contact phase and may eventually merge into a single massive star. This merger would be dramatic, potentially leading to a supernova or even the formation of a black hole. While the exact future is uncertain, the system’s evolution will help refine models of stellar interactions and the role of binaries in the production of gravitational waves.

Challenges and Next Steps

Although the current data provides strong evidence for WLM-CB1 being a contact binary, more observations are needed. Spectroscopic data could confirm the mass and composition of the stars. Such data would help clarify whether the stars are truly in contact or merely very close. Future observations from new telescopes, like those coming from the Vera C. Rubin Observatory, could uncover even more systems like WLM-CB1, deepening our understanding of binary star evolution in metal-poor environments.

Conclusion

The discovery of WLM-CB1 provides a rare glimpse into the early phases of a stellar merger in a low-metallicity environment. It’s a powerful example of how advanced telescopes like Hubble and Webb can open new windows into the universe, especially as astronomers continue to push the limits of what we know about the life and death of massive stars.

Source: Gull