The first image of a star outside the Milky Way illuminates the final moments before its explosive end.
This image is the first-ever closeup of a star outside the Milky Way. The bright oval is gas and dust enveloping WOH G64, suggesting the star is undergoing its final stages before it erupts into a supernova. Credit: ESO/K. Ohnaka et al.
After years of effort, astronomers at the European Southern Observatory (ESO) announced they managed to capture the first closeup image of a star beyond our galaxy. This remarkable achievement offers more than just stunning visuals — it provides a rare glimpse into the final moments of a star that will inevitably explode as a spectacular supernova.
The red supergiant star, WOH G64, is one of the largest and most luminous stars in the Large Magellanic Cloud (LMC), a satellite galaxy of the Milky Way. With a size at least 2,000 times that of our Sun, WOH G64 is an absolute behemoth. If it were to take the place of our Sun, its glowing edges would extend to the orbit of Saturn.
WOH G64 is located 160,000 light-years away in the constellation Dorado, meaning the light we see emanating today, as bright as it is, left the star 160,000 years ago. The star’s explosive demise was sealed when it was born with a mass roughly 25 to 40 times that of our Sun. Massive stars like this one are known to end their lives by imploding dramatically after exhausting the nuclear fuel in their cores. But before its explosive finale, WOH G64 spends thousands of years undergoing a violent transformation — akin to a cosmic time bomb, but on a scale that stretches far beyond human lifetimes.
The new image, taken in December 2020 using the European Southern Observatory’s Very Large Telescope Interferometer (VLTI) rooted in Chile’s Atacama Desert, captures crucial signs of the star’s impending demise. For instance, the star returned to a quiescent state in 2014 after erupting for some three decades. All that expelled material now envelops the star as a previously unseen egg-shaped cocoon brought into focus in the new image. The bright, dusty cocoon could even be sculpted by an unseen, bluish-white companion star that may well be accreting some of the material expelled by WOH G64, researchers say.
“For the first time we have been able to see the structures that wrap a star in its death throes,” study co-author Jacco van Loon of the Keele Observatory in the U.K., who’s been studying WOH G64 since the 1990s, told Reuters. “Even in our Milky Way Galaxy we do not have such an image.”
The latest image also shows an elliptical ring surrounding the dusty cocoon, which was first spotted in 2007 and still persists. Astronomers estimate the ring spans anywhere between 120 to 30,000 times the distance between Earth and the Sun. While various algorithms have reconstructed the ring, forthcoming observations would definitively determine whether it is truly a ring of shed dust or merely a photographic artifact, according to a paper outlining the imaging effort, which was published late last month in the journal Astronomy & Astrophysics.
The researchers note WOH G64’s mass-loss behavior and circumstellar material may be reminiscent of the events leading up to the extensively studied supernova SN1987A in the LMC. Observations of SN1987A with the Hubble Space Telescope had revealed its progenitor star was a red supergiant about 20,000 years before its explosion, and may have expelled ring-shaped material similar to what we see around WOH G64. “If this is what we are seeing (WOH G64) doing, then a spectacle awaits us soon,” van Loon told CNN.
Astronomers attribute the stunning new image to GRAVITY, a newer, highly sensitive instrument installed on VLTI that combines light from four telescopes to achieve a resolution so sharp one could distinguish a person walking on the Moon. However, WOH G64 itself is not visible in the image, as it is either too faint or entirely obscured by the dust it has shed, the researchers say. By comparing the new results with previous observations of the star, the study team concluded the star dimmed significantly during the past decade, yet another indication of its imminent death.
“This star is one of the most extreme of its kind, and any drastic change may bring it closer to an explosive end,” van Loon said in a statement.
