For the first time, astronomers have captured a close-up image of a dying star beyond our Milky Way. This milestone, achieved by the European Southern Observatory’s Very Large Telescope Interferometer (VLTI), brings the red supergiant WOH G64 into sharp focus, revealing it shrouded in a strange, egg-shaped cocoon of gas and dust. The star’s story is as captivating as the techniques used to unveil it.
A Cosmic Behemoth
Located in the Large Magellanic Cloud, a satellite galaxy 160,000 light-years away, WOH G64 is no ordinary star. Known as the “behemoth star,” it dwarfs our Sun with a size roughly 2,000 times greater. Scientists have studied it for decades but, until now, its body and surroundings remained hidden from view.
“For the first time, we have succeeded in taking a zoomed-in image of a dying star in a galaxy outside our own Milky Way,” said Keiichi Ohnaka, lead researcher and astrophysicist at Universidad Andrés Bello in Chile. The discovery offers a rare opportunity to witness the death throes of a star as it nears a dramatic supernova explosion.
WOH G64 is a red supergiant, a type of star in its final stage of life. These colossal stars eject their outer layers over thousands of years, forming halos of material. However, the VLTI image revealed a surprising detail: the star’s “cocoon” of gas and matter is not spherical but stretched out, resembling an egg.
“We discovered an egg-shaped cocoon closely surrounding the star,” Ohnaka added. “We are excited because this may be related to the drastic ejection of material from the dying star before a supernova explosion.”
A Glimpse Into the End
Astronomers like Gerd Weigelt of the Max Planck Institute for Radio Astronomy see WOH G64 as an extraordinary case study. “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 Weigelt, who is also co-author of the study.
This real-time transformation is evident in the star’s dimming over the past decade. The team attributes this fading to the thickening layers of gas and dust expelled by the star. Jacco van Loon, Keele Observatory Director, highlighted that “This star is one of the most extreme of its kind, and any drastic change may bring it closer to an explosive end.”
While the dimming complicates future observations, new upgrades to the VLTI, including the GRAVITY+ instrument, could help astronomers track WOH G64’s final act. The cocoon’s peculiar shape may also hint at the presence of a hidden companion star, subtly altering the dynamics of the gas and dust around WOH G64.
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A Telescope That Peers Beyond
The VLTI’s ability to image this distant star is a triumph of modern astronomy. Its GRAVITY instrument combines light from four telescopes to achieve unmatched precision, enabling researchers to study objects too faint or distant for other methods. WOH G64 is the first star beyond the Milky Way to be captured with this level of detail, but it is unlikely to be the last.
“Similar follow-up observations with ESO instruments will be important for understanding what is going on in the star,” Ohnaka said. These tools will allow astronomers to delve deeper into the life cycles of stars in other galaxies, helping us understand the universe’s broader workings.
The findings appeared in the Astronomy & Astrophysics.