In the Large Magellanic Cloud, one of the satellite galaxies of the Milky Way, 163,000 light years from us, is WOH G64, a huge star 2,000 times larger than our Sun. Although it was discovered by European astronomers in the years 90, Keiichi Ohnaka, an astrophysicist at the Andrés Bello University of Chile, has been working around it for more than a decade. And although his professional career revolves, like a planet, around WOH G64, he had not been able to see it ‘face to face’ until now, when thanks to the Very Large Telescope of the European Southern Observatory (ESO’s VLTI) it has been possible to photograph it in close-up of this monster, which is also in the last stages of its life. At least as a star. The results have just been published in the journal ‘Astronomy & Astrophysics‘.
Ohnaka’s team discovered in 2008 that this star, the largest in its galaxy and classified as a red supergiant – which indicates that, despite its large size, it is not very dense – was surrounded by an enormous ring of gas and dust. The researchers pointed out that this ‘stellar donut’ around it has probably been created because it is losing mass in a violent way, which indicates that we are facing a dying star. Since then, the group led by Ohnaka has been studying WOH G64, although until now it had not been possible to obtain a real image of the star and confirm their suspicions, although with some surprises.
Waiting for the right technology
To obtain the desired image, the team had to wait for the development of one of the VLTI’s second generation instruments, GRAVITY. This instrument, which has been making regular observations since 2016, represented a huge advance in sensitivity and precision compared to previous instruments that use interferometry, a technique that combines light from different telescopes to allow astronomers to pick up tiny details in faint objects. .
On the left, the real image captured by the VLTI telescope. On the left, the artistic representation of the same star
Astronomers were able to capture, in fact, the halo of dust and gas that surrounds the star, although their ‘egg’ shape caught their attention. “We are excited because this may be related to the drastic ejection of material from the dying star before a supernova explosion,” says Ohnaka. That is to say, the eruptions that the dying star is suffering in this last stage of its life are causing the material to be distributed irregularly, creating that curious cocoon shape or even a yet undiscovered companion is exerting its influence, creating with its gravity this curious shape.
“This star is one of the most extreme of its type, and any drastic change can bring it closer to an explosive end,” says Jacco van Loon, director of the Keele Observatory at Keele University (United Kingdom). also a signatory of the article and one of the researchers who has been observing this giant since the 1990s.
Shape change in recent times
With the results of the observations they also carried out a comparison with old data and here came the surprise: the star has dimmed significantly in the last decade. “We have discovered that WOH G64 has been undergoing a significant change over the last 10 years, providing us with a unique opportunity to witness the life of a star in real time,” says Gerd Weigelt, professor of astronomy at the Max Planck Institute for Radio Astronomy in Bonn (Germany) and co-author of the study.
In their final stages of life, red supergiants shed their outer layers of gas and dust in a process that can last thousands of years. In this phenomenon, a point is reached at which the core is no longer able to generate enough energy to ‘sustain’ the enormous stellar mass, and it collapses due to its own gravity until the star, unable to withstand the immense pressure, It explodes releasing an immense amount of energy, becoming a supernova.
Other red supergiants
WOH G64 is not the only intriguing star of its kind: of this same class is the enigmatic Betelgeuse, which experienced a sudden dimming of more than half of its brightness in 2019 that made astronomers think that we could witness death live. of one of these giants. However, shortly afterward it regained its light – further disconcerting scientists, who are still considering various theories about what happened – which indicated that the explosion would be expected at least a little longer.
Apart from the spectacular nature of the supernova, when a star becomes fainter it also has other consequences, such as making it increasingly difficult for our instruments to see them. Much more so in the case of distant stars like WOH G64, who have been so ‘elusive’ for so many years. However, astronomers have a lot of hope for future instruments, such as planned upgrades to VLTI instrumentation and the future GRAVITY+. “Similar follow-up observations with ESO instruments will be important to understand what is happening in the star,” concludes Ohnaka.
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