A first detailed image of a star more than 160,000 light years away, outside our galaxy

Scientists from the European Southern Observatory (ESO) have succeeded in taking a detailed image of a star in a galaxy other than our Milky Way, a first which will allow them to better study this star at the end of its life. 160,000 light years distant, the star WOH G64 is located in the Large Magellanic Cloud, a small satellite galaxy of ours.

Nicknamed “the colossal star” by astronomers, it is approximately 2000 times larger than our Sun and is classified among the red supergiants, one of the last stages in the evolution of massive stars before their explosion as a supernova. “We discovered an egg-shaped cocoon tightly surrounding the star”details in a statement from the ESO Keiichi Ohnaka, astrophysicist at the Andrés Bello University in Chile.

“The ovoid shape in the center represents material ejected by the central star and still surrounding it. We can also see another oval ring surrounding this ovoid shape. Although additional observations are needed to definitively confirm this, we believe this ring is also made up of material ejected from the star.describes the astrophysicist.

Ejection of matter before its disappearance

The scientists had «indices» that the star's environment was not spherical, but no images had been taken until now. “With this image, we can create a better computer model of the star and study how it ejects material before it disappears”explains the researcher, who led a study on these observations, published Thursday in the journal «Astronomy & Astrophysics».

This elongated cocoon, a sign that the star “ejects more material in some directions than in others”could be a consequence of its interaction with another star, according to Keiichi Ohnaka. “Although we have not yet found a second star, such a companion could exist and still be difficult to detect if it is much fainter than the main star”he says.

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Loss of brightness

Keiichi Ohnaka's team has been interested in this giant star for a long time. In 2005 and 2007, these astronomers used the ESO Very Large Telescope Interferometer (VLTI) in Chile to learn more about its characteristics. But at the time, the interferometer only combined light from two of the VLT's telescopes. To obtain the image released Thursday, astronomers had to wait for the development of the Gravity instrument, which captures light from four glasses, creating very detailed cosmic images.

Comparing these new results with previous observations, they found that WOH G64 had become less bright over the past decade. She has “undergone significant change over the past ten years, giving us a rare opportunity to observe the life of a star in real time”declares Gerd Weigelt, co-author of the study cited in the press release and professor of astronomy at the Max Planck Institute in Bonn (Germany).

Potential end of life

In their final stages of life, before exploding as a supernova, red supergiants lose their outer layers of gas and dust, in a process that can last hundreds of thousands of years. Scientists who observed WOH G64 believe that the expelled material could be responsible for its dimming and that this could mean that the star has entered a new phase of its end-of-life cycle.

“Or it could return to its previous state after a while, although we don't know how long that might take. It is precisely for this reason that we think it is important to monitor this star by observing it with different telescopes and instruments.souligne Keiichi Ohnaka.

As the star dims, it becomes increasingly difficult to take further close-up images, even with VLTI. But planned updates to the telescope's instruments could change that soon.