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A star cloaked in an egg-shaped cocoon has been revealed in the first detailed images of a star beyond the Milky Way.
Until now, stars in other galaxies have been visible as little more than points of light, even when observed using telescopes. Now, thanks to the European Southern Observatory’s Very Large Telescope Interferometer (VLTI), astronomers have captured the first zoomed-in image.
“We discovered an egg-shaped cocoon closely surrounding the star,” said Dr Keiichi Ohnaka, an astrophysicist at the Andrés Bello National University in Chile. “We are excited because this may be related to the drastic ejection of material from the dying star before a supernova explosion.”
The star, called WOH G64, is located 160,000 light years away in the Large Magellanic Cloud, one of the small galaxies that orbits the Milky Way. It is thought to be the largest star in the galaxy, classified as a red supergiant and about 2,000 times the mass of the sun. Even so, observing the behemoth star in detail still required a resolution equivalent to seeing an astronaut walking on the moon from Earth.
“We’re not able to do that with normal telescopes,” said Dr Jacco van Loon, a reader in astrophysics at Keele University and a co-author of a paper outlining the observations published in the journal Astronomy & Astrophysics.
The images reveal the star is undergoing a dramatic transition and suggest that in the past decade or so it has blown off its outer layer, leaving it surrounded by an egg-shaped cocoon of gas and dust. The elongated shape could be explained by either the star’s rotation or by the influence of a yet-undiscovered companion star.
This, the scientists say, could signal the star entering a final stage of life before it becomes a supernova. “Massive stars explode with an energy equivalent to the Sun shining for all of its 10bn years of life,” said Van Loon. “People have seen these supernova explosions, and astronomers have found some of the stars that exploded in older images. But we have never seen a star change in a way that signals its imminent death.”
There is evidence that some stars appear to throw off their outer layers just years or decades before reaching their demise in a supernova. But seeing things unfold in real time is not guaranteed. “It might still be tens of thousands of years,” said Van Loon. “For an astronomer that’s imminent because stars live millions or billions of years.”
