Significant mass loss in the red supergiant (RSG) phase is essential for the evolution of massive stars before they end their life in a supernova (SN) explosion. The red supergiant at advanced evolutionary stages experiences drastic mass loss.
Recent analyses of very early-phase spectra of supernova explosions taken within a day after the explosion suggest significant increases in the mass-loss rate in the RSG phase before the SN explosion.
WOH G64 or IRAS 04553-6825 or behemoth star is an unusual red supergiant (RSG) star in the Large Magellanic Cloud (LMC). It is the largest known star with a well-defined radius and one of the most luminous and massive red supergiants, with a radius around 1,540 times that of the Sun.
Credit:
ESO/K. Ohnaka et al.
For the first time, astronomers have successfully captured the first close-up picture of WOH G64. They captured the image using the European Southern Observatory’s Very Large Telescope Interferometer (ESO’s VLTI).
The observations revealed that the star was on the verge of becoming a supernova, emitting gas and dust.
Scientists measured the temperature of red supergiant stars
They also found that the star is surrounded by an egg-shaped cocoon- a sign of the drastic ejection of material from the dying star before a supernova explosion.
Keiichi Ohnaka, an astrophysicist from Universidad Andrés Bello in Chile, and the team had long been interested in this behemoth star. In 2005 and 2007, using ESO’s VLTI in Chile’s Atacama Desert, they learned more about the star’s features and continued to study it. However, an actual image of the star had remained elusive.
The new image, taken with the VLTI’s GRAVITY instrument, shows that the star is enveloped in a large egg-shaped dust cocoon. The image on the right shows an artist’s impression reconstructing the geometry of the structures around the star, including the bright oval envelope and a fainter dusty torus. Confirming the presence and shape of this torus will require additional observations.
Credit:
ESO/K. Ohnaka et al., L. Calçada
To obtain the desired image, the team waited for the development of one of VLTI’s second-generation instruments, GRAVITY. They compared their new results with other previous observations and found surprising results: The star had become dimmer over the past decade.
Gerd Weigelt, an astronomy professor at the Max Planck Institute for Radio Astronomy in Bonn, Germany, and a co-author of the study said, “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.”
“This star is one of the most extreme of its kind, and any drastic change may bring it closer to an explosive end,” adds co-author Jacco van Loon, Keele Observatory Director at Keele University, UK, who has been observing WOH G64 since the 1990s.
Astronomers believe these shed materials might be responsible for the dimming and unexpected shape of the dust cocoon around the star. In the new image, the dust cocoon seems stretched out.
The team believes that the cocoon’s egg-like shape could be explained by the star’s shedding or by the influence of a yet-undiscovered companion star.
Journal Reference
- K. Ohnaka, K.-H. Hofmann, G. Weigelt, J. Th. van Loon, D. Schertl, S.R. Goldman. Imaging the innermost circumstellar environment of the red supergiant WOH G64 in the Large Magellanic Cloud. Astronomy & Astrophysics. DOI: 10.1051/0004-6361/202451820