Astronomers have observed an extraordinarily rare transformation in one of the largest known stars in the universe, WOH G64, signaling its imminent demise. The star, located in the Large Magellanic Cloud approximately 160,000 light-years from Earth, has rapidly shifted from a supergiant red star to a hypergiant yellow star, a change detected over the past decade.
The transition, noted as occurring on a cosmic timescale but remarkably swift in human terms, has baffled researchers due to the absence of typical accompanying phenomena like stellar flares or explosions. “Usually, stellar evolution happens on timescales of billions of years. On human timescales, we only observe more sudden and violent events, such as eruptions, the merging of two stars, or the explosive death of a star,” explained Gonzalo Muñoz-Sanchez, the lead author of a study published this week in the journal Nature Astronomy.
WOH G64 is estimated to have a mass roughly 28 times that of our Sun, but its diameter is approximately 1,500 times larger. If positioned at the center of our solar system, its surface would extend beyond the orbit of Saturn. The star is relatively young, at around 10 million years old, contrasting sharply with our Sun’s 4.5 billion-year age and projected lifespan of another 5 billion years.
Stars with masses between eight and 23 times that of the Sun are generally expected to evolve into red supergiants and eventually explode as supernovae. Yet, the fate of stars with masses between 23 and 30 solar masses, like WOH G64, remains uncertain. Scientists are currently unsure whether these massive stars will detonate as supernovae, collapse directly into black holes, or undergo a transition from a red supergiant phase to a yellow hypergiant phase before their final moments.
Adding to the complexity of studying WOH G64 is its existence within a binary star system, gravitationally bound to another star. Researchers have yet to determine the size or characteristics of the companion star, but speculate that the two stars may eventually merge. Recent observations from the James Webb Space Telescope have also uncovered details about former stars that have exploded as supernovae, providing further context to the study of stellar evolution [3].
The dramatic changes observed in WOH G64 are also occurring as scientists continue to monitor other massive stars in the universe, including observations of changes in one of the universe’s biggest stars [1]. Meanwhile, NASA is tracking a massive iceberg in the Southern Ocean that is predicted to completely disintegrate in the coming days [2], and researchers are even considering the possibility of using nuclear weapons to deflect potentially hazardous asteroids [4].
