A recent study in Astronomy & Astrophysics asserted that the European Southern Observatory’s Very Large Telescope Interferometer (ESO’s VLTI) provided the remarkable sharpness needed to image the star WOH G64, which is an astounding 160,000 light-years away from Earth.
This is an image of the star WOH G64, taken by the GRAVITY instrument on the European Southern Observatory’s Very Large Telescope Interferometer (ESO’s VLTI). This is the first close-up picture of a star outside our own galaxy, the Milky Way. The star is located in the Large Magellanic Cloud, over 160 000 light-years away. The bright oval at the centre of this image is a dusty cocoon that enshrouds the star. A fainter elliptical ring around it could be the inner rim of a dusty torus, but more observations are needed to confirm this feature. Image Credit: ESO/K. Ohnaka et al.
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.
Keiichi Ohnaka, Study Lead Author and Astrophysicist, Universidad Andrés Bello
The new observations show a star puffing forth gas and dust in its final stages before it explodes as a supernova.
Ohnaka added, “We discovered an egg-shaped cocoon closely surrounding the star. We are excited because this may be related to the drastic ejection of material from the dying star before a supernova explosion.”
There are many more stars in other galaxies, so far away that it has been very difficult to observe even one of them in detail, even though astronomers have acquired roughly two dozen zoomed-in images of stars in the galaxy, revealing their features.
WOH G64, the newly imaged star, is located in the Large Magellanic Cloud, a tiny galaxy that circles the Milky Way. Astronomers have known about this star for decades, and it has been properly named the ‘behemoth star’. WOH G64 is a red supergiant, with a size about 2000 times that of our Sun.
Ohnaka’s team had long been interested in this massive star. They studied the star's peculiarities using ESO’s VLTI in Chile’s Atacama Desert in 2005 and 2007 and have continued to do so in subsequent years. However, a real image of the star remained elusive.
To obtain the desired image, the team had to wait for the creation of one of the VLTI’s second-generation equipment, GRAVITY. After comparing their new findings to prior observations of WOH G64, they were astonished to discover that the star had dimmed over the previous decade.
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.
Gerd Weigelt, Study Co-Author and Professor, Max Planck Institute for Radio Astronomy
In their last stages of life, red supergiants such as WOH G64 shed their outer layers of gas and dust, a process that can take thousands of years.
This star is one of the most extreme of its kind, and any drastic change may bring it closer to an explosive end.
Jacco van Loon, Study Co-Author and Director, Keele Observatory, Keele University
The team believes these shed components are also responsible for the dimming and the unusual shape of the dust cocoon surrounding the star. The new image shows the extended cocoon, surprising scientists who predicted a different form based on earlier observations and computer models. The cocoon’s egg-like structure, the team stated, might be explained by either the star’s shedding or the effect of an undiscovered companion star.
As the star fades, capturing more close-up images gets progressively difficult, even for the VLTI. Nonetheless, planned improvements to the telescope’s hardware, such as the forthcoming GRAVITY+, promise to change this.
Ohnaka concluded, “Similar follow-up observations with ESO instruments will be important for understanding what is going on in the star.”
Journal Reference:
Ohnaka, K. et. al. (2024) Imaging the innermost circumstellar environment of the red supergiant WOH G64 in the Large Magellanic Cloud. Astronomy and Astrophysics. doi.org/10.1051/0004-6361/202451820