Astronomers from Russia have recently conducted an extensive set of photometric observations of an exceptionally rare star, DDO68-V1, shedding light on its behavior and variability. This unique star, a luminous blue variable (LBV), has been the subject of intense study due to its extreme characteristics. The findings, published on January 28 on the arXiv pre-print server, provide a deeper understanding of this star’s dramatic variability, offering important insights into the evolution of massive stars and the processes at play in their later stages.
Understanding Luminous Blue Variables (LBVs)
Luminous blue variables are massive, unstable stars in one of the final evolutionary stages of their life cycle. These stars are rare, and their defining characteristic is their photometric and spectroscopic variability. They undergo massive, transient eruptions that significantly alter their luminosity and spectral characteristics. Due to their unstable nature, LBVs are thought to play an essential role in the stellar evolution of massive stars, particularly in how they lose mass. Their study helps astronomers understand the final phases of high-mass stars before they end their lives, either through supernova explosions or by shedding vast amounts of material.
What makes LBVs especially intriguing is the extreme variability they exhibit. Some LBVs undergo outbursts, dramatically altering their brightness over short periods. These eruptions often result in significant mass loss, and the material ejected can influence the surrounding interstellar medium. Therefore, understanding how LBVs behave during these outbursts is crucial for better modeling the life cycle of massive stars.
DDO68-V1: A Star with Extreme Characteristics
DDO68-V1 is an extremely metal-poor LBV located in the dwarf irregular galaxy DDO 68, situated about 41.2 million light-years from Earth. What makes this star particularly notable is its incredibly low metallicity, which is a key feature of the galaxy it inhabits. DDO 68 is one of the most metal-poor galaxies ever discovered, making it a valuable object of study for astronomers seeking to understand the conditions that existed in the early universe.
Discovered in 2008, DDO68-V1 underwent a significant eruption between 2008 and 2011, during which its brightness increased dramatically. This outburst is one of the most remarkable features of the star, as such eruptions are a hallmark of LBVs. The eruption made DDO68-V1 one of the few LBVs to have been observed in such a dramatic phase, providing a rare opportunity to study this kind of event in a star with extremely low metallicity.
New Observations and Study Goals
The study led by Simon A. Pustilnik and his team at the Special Astrophysical Observatory (SAO) in Russia aimed to investigate the behavior of DDO68-V1 over an extended period. The team analyzed archival data spanning over 36 years, with the goal of gaining a more detailed understanding of this star’s variability. In doing so, they sought to improve their knowledge about the evolutionary stage of LBVs and the underlying mechanisms that cause the powerful variability and mass loss observed in such stars.
The study found that DDO68-V1 exhibits a high degree of variability. Over the span of more than three decades, the star was in a “low” state—a phase where its brightness was relatively stable—only during six short intervals, each lasting less than one year. This suggests that the star remains in a highly active state for the majority of the time, experiencing significant changes in luminosity.
Key Findings and Light Curve Behavior
The light curve of DDO68-V1, which charts the star’s brightness over time, showed a wide range of variability. In particular, the star’s brightness in the V-band (a specific band of light in the visible spectrum) fluctuated between 20.0 and 25.0 magnitudes. This is a considerable variation, corresponding to an absolute magnitude range between -5.9 and -10.8, indicating large changes in its luminosity.
The most striking feature of the study was the major brightening of DDO68-V1 during the eruption that took place between 2008 and 2011. After the eruption, the star began to fade, losing about 2.0 magnitudes by 2013. However, the light variations that followed this major event were characteristic of typical LBVs. The amplitude of these variations, which reached between 3.0 and 3.5 magnitudes, is much larger than what has been observed in other well-studied LBVs, suggesting that DDO68-V1 may exhibit more dramatic and frequent changes than most stars in this category.
These findings point to the fact that DDO68-V1 is not just an ordinary LBV, but rather one with highly exaggerated fluctuations in brightness. This highlights the uniqueness of the star and emphasizes the need for further study to understand its behavior more thoroughly.
Future Monitoring: The Path Forward
Given the high degree of variability observed in DDO68-V1, the researchers suggest that high-cadence multiband monitoring of the star should be conducted over the next several years. Continuous monitoring, especially with instruments capable of observing in multiple wavelength bands, could provide more precise data on the star’s light curve and variability patterns. By improving the temporal and spectral resolution of observations, astronomers would be better equipped to probe the star’s internal processes and reveal potential periodic signals that might be hidden due to the internal variability associated with LBV phenomena.
The researchers propose that ongoing observation could also reveal important details about the star’s color changes over time. These color variations could provide insights into the mechanisms driving the variability and mass loss of the star, potentially helping to determine whether DDO68-V1 is part of a binary system—a possibility that has yet to be confirmed. Observations could also help establish characteristic times for its variability, offering clues to the underlying processes causing the star’s dramatic outbursts and changes.
Conclusion
The study of DDO68-V1 has provided crucial new insights into the variability and mass loss of luminous blue variables, especially in a star with such an unusual, extremely low metallicity. The findings suggest that the star is much more active and unpredictable than previously thought, with larger-than-expected fluctuations in its brightness. The data also emphasize the need for further monitoring and analysis to understand the complex processes at work in this remarkable object.
As luminous blue variables remain one of the most fascinating and enigmatic types of stars, ongoing research into stars like DDO68-V1 could lead to significant advancements in our understanding of stellar evolution, mass loss, and the final stages of massive star life cycles. This work will help to refine models of star evolution, providing a deeper understanding of how such stars evolve and eventually end their lives. The discovery of DDO68-V1’s extreme variability highlights just how much there is still to learn about the most massive and dynamic stars in the universe.
Reference: S. A. Pustilnik et al, On variability of DDO68-V1, a unique extremely metal-poor LBV, arXiv (2025). DOI: 10.48550/arxiv.2501.16810