Team Led by UNAB Astrophysicist Captures First Close-Up Image of a Supergiant Star Outside Our Galaxy

“For the first time, we have obtained an enlarged image of a dying star in a galaxy outside our own Milky Way,” said Keiichi Ohnaka, a researcher at the Institute of Astrophysics at UNAB and leader of the team responsible for this achievement. Located 160,000 light-years away, WOH G64 was photographed with unprecedented clarity thanks to ESO’s Very Large Telescope Interferometer (VLTI).

“We discovered an egg-shaped envelope closely surrounding the star,” explained Ohnaka, the lead author of the study published in Astronomy & Astrophysics. “We are excited because this may be related to the dramatic ejection of material from the dying star before a supernova explosion.”

This breakthrough marks a significant milestone in astronomy. Due to their vast distances, detailed observations of stars in other galaxies have long been an extreme challenge.

A Collaboration of International Experts

The research team, led by UNAB astrophysicist Keiichi Ohnaka, included Karl-Heinz Hofmann, Gerd Weigelt, and Dieter Schertl from the Max Planck Institute for Radio Astronomy in Germany; Jacco van Loon from Keele University in the United Kingdom; and Steven R. Goldman from the Space Telescope Science Institute in the United States.

A Supergiant Star

WOH G64 resides within the Large Magellanic Cloud, one of the smaller galaxies orbiting the Milky Way. Known as the “giant star,” it has been studied by astronomers for decades. At 2,000 times the size of the Sun, WOH G64 is classified as a red supergiant.

Ohnaka’s team has long been interested in this massive star. In 2005 and 2007, they studied its characteristics using ESO’s VLTI, located in Chile’s Atacama Desert. Despite years of research, capturing an actual image of the star remained an elusive goal.

This changed with the development of GRAVITY, a second-generation instrument for the VLTI. GRAVITY enabled the team to record an enlarged image of WOH G64, previously thought impossible. Comparing their findings with earlier computational models of the star, the researchers were surprised to discover that it had dimmed significantly over the past decade.

Witnessing the End

“We have found that the star has undergone a significant change in the last 10 years, providing us with a unique opportunity to observe a star’s life in real-time,” said Gerd Weigelt, an astronomy professor at the Max Planck Institute for Radio Astronomy in Bonn, Germany, and co-author of the study.

As they near the end of their lives, red supergiants like WOH G64 shed their outer layers of gas and dust, a process that can span thousands of years. “This star is one of the most extreme of its kind, and any drastic changes could bring it closer to an explosive end,” added co-author Jacco van Loon, director of the Keele Observatory at Keele University in the UK, who has been observing WOH G64 since the 1990s.

The team believes that the materials expelled by the star are responsible for its dimming and the unexpected shape of the surrounding dust envelope. The new image reveals the envelope to be elongated, surprising the researchers, who had anticipated a different shape based on earlier observations and models. The team speculates that an as-yet-undiscovered companion star may influence the egg shape.

“To understand what is happening with the star, follow-up observations using ESO’s instruments will be essential,” concluded Ohnaka.

The Technology Behind the Discovery

ESO’s Very Large Telescope Interferometer (VLTI) combines the light collected by the VLT’s telescopes—either its four 8-meter units or smaller auxiliary telescopes—creating extraordinarily detailed images of the cosmos. This setup acts as a “virtual” telescope with a resolution equivalent to the maximum distance between the individual telescopes.

Earlier instruments like MIDI enabled pioneering observations, but the arrival of GRAVITY—a second-generation VLTI instrument capable of combining light from four telescopes—greatly enhanced sensitivity and resolution, making the imaging of WOH G64 possible.

As WOH G64 continues to dim, capturing enlarged images becomes increasingly challenging, even for the VLTI. However, upcoming technological upgrades like GRAVITY+ promise to overcome these limitations, enabling observations of fainter and more distant objects.