"We discovered an egg-shaped cocoon closely surrounding the star," explained Ohnaka, the lead author of a study published in 'Astronomy and Astrophysics'. "We are excited because this may be related to the drastic ejection of material from the dying star before a supernova explosion."
Until now, astronomers have primarily imaged stars in the Milky Way, with about two dozen such zoomed-in images available. However, observing stars in other galaxies in similar detail has proven nearly impossible due to their distance. The imaging of WOH G64 marks a significant step forward in studying extragalactic stars.
Astronomers have known about WOH G64 for decades, referring to it as the "behemoth star" due to its immense size - approximately 2,000 times that of the Sun. Ohnaka's team first investigated the star's properties in 2005 and 2007 using the VLTI in Chile's Atacama Desert, but capturing a detailed image required the advent of the GRAVITY instrument, part of the VLTI's second generation of tools.
Upon comparing the newly captured image with previous observations, researchers noted a surprising dimming of the star over the past decade. "We have found that the star has been experiencing a significant change in the last 10 years, providing us with a rare opportunity to witness a star's life in real time," said Gerd Weigelt, an astronomy professor at the Max Planck Institute for Radio Astronomy in Bonn, Germany, and co-author of the study.
Red supergiants like WOH G64 gradually shed their outer layers in a process that can last thousands of years. Co-author Jacco van Loon, director of Keele Observatory at Keele University, UK, noted, "This star is one of the most extreme of its kind, and any drastic change may bring it closer to an explosive end."
The egg-like shape of the cocoon surrounding WOH G64 surprised researchers, as it deviates from predictions based on earlier models. The team speculates that the unusual shape may result from uneven material shedding or the influence of an unseen companion star.
Although WOH G64 continues to dim, making future imaging more challenging, forthcoming upgrades to the VLTI, such as the GRAVITY+ instrument, promise to enhance observational capabilities. "Similar follow-up observations with ESO instruments will be important for understanding what is going on in the star," Ohnaka concluded.
Research Report:Imaging the innermost circumstellar environment of the red supergiant WOH G64 in the Large Magellanic Cloud
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Stellar Chemistry, The Universe And All Within It
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