PISA, Italy — Massive stars that ultimately collapse into black holes are likely shedding much more material during their brief lifespans than previously understood, according to new research. A team of astronomers has determined that these stellar giants, some exceeding 100 times the mass of the sun, produce extraordinarily powerful stellar winds capable of ejecting their outer layers into space.
The study, led by researchers at the Institute for Advanced Study in Italy, highlights the role of these stellar winds in shaping the lifecycle of these massive stars. Team member Kendall Shepherd emphasized that these winds are intense, comparing them to “hurricanes” rather than gentle breezes. While a typical star like the sun has a lifespan of approximately 10 billion years, these massive stars exist for just a few million years, burning through their nuclear fuel at an alarming rate.
Understanding these stars is crucial, as they significantly influence their cosmic environments despite their fleeting existence. The winds generated by these gigantic stars, along with their eventual supernova explosions, distribute newly formed elements throughout space. Many of these elements contribute to the formation of new stars, while others, such as carbon and oxygen, are essential for life.
Shepherd explained the importance of recent observations of massive stars in the Tarantula Nebula, located about 160,000 light-years from Earth. The findings revealed a category of extremely luminous stars, known as Wolf-Rayet stars, which are nearing the end of their hydrogen-burning phase. These stars exhibit temperatures considerably higher than previously predicted, presenting a challenge to existing stellar evolution models.
The researchers implemented a new mass-loss model into their stellar evolution code to reconcile observational data with theoretical predictions. This updated model suggests that stronger stellar winds are responsible for stripping away a star’s outer layers, enabling it to maintain a high temperature for an extended period. The newly calibrated model aligns with the observed properties of these stars, indicating a more complex interaction than previously believed.
The research also addresses the formation of the most massive star known, R136a1, which exists in the Tarantula Nebula. R136a1 is estimated to be about 230 times the mass of the sun and produces millions of times more energy. The findings propose two potential pathways for its formation: as a single gigantic star or through a merger of two smaller stars. Shepherd noted the surprising implications of these scenarios for our understanding of stellar mass limits within the universe.
Furthermore, this study sheds light on how these stronger winds influence the resulting black hole populations. The dramatic mass loss caused by powerful stellar winds could lead to the formation of smaller black holes, challenging current models that account for a greater variety of black hole sizes, particularly the elusive intermediate-mass black holes.
The implications extend even further, with the research suggesting that stronger stellar winds may facilitate the creation of black hole binaries that are more massive than previously assumed. These findings are significant for gravitational wave astronomy, as such black holes produce detectable ripples in spacetime during their mergers.
Looking ahead, Shepherd indicates that the team plans to expand their research beyond the Tarantula Nebula to investigate how different chemical environments across the universe may affect black hole formation. By refining their models to account for varied initial conditions, researchers aim to enhance our understanding of black hole populations on a broader scale.