A star encased 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 were only visible as points of light, even when observed with 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 that now surrounds the star,” said Dr Keiichi Ohnaka, an astrophysicist at the Andrés Bello National University in Chile. “We are excited because this could be related to the drastic ejection of material from the dying star before a supernova explosion.”
The star, named WOH G64, is located 160,000 light-years away in the Large Magellanic Cloud, one of the small galaxies orbiting 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 still required a resolution equivalent to an astronaut walking on the moon from Earth.
“We are not able to do this with normal telescopes,” said Dr Jacco van Loon, a reader in astrophysics at Keele University and a co-author of a paper detailing the observations published in the journal . Astronomy & Astrophysics.
The images reveal that the star is undergoing a dramatic transition, suggesting that in the past decade or so it has shed its outer layer, leaving it surrounded by an egg-shaped cocoon of gas and dust. The elongated shape can be explained either by the star’s rotation or by the influence of an as yet undiscovered companion star.
This, the scientists say, could indicate that the star is entering a final phase of life before going supernova. “Massive stars explode with an energy equivalent to the sun shining for all its 10 billion 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 indicates its imminent death.”
There is evidence that some stars appear to shed their outer layers just years or decades before they reach their demise in a supernova. But seeing things unfold in real time is not guaranteed. “It could be tens of thousands of years,” van Loon said. “To an astronomer, it’s imminent because stars live millions or billions of years.”
