Saturday, July 25, 2015

WOH G64 is a Stellar Behemoth with a Thick Disk

Artist’s impression of WOH G64. Credit: ESO.

WOH G64 is a remarkable red supergiant (RSG) star located 163,000 light years away in the Large Magellanic Cloud (LMC), a satellite galaxy of the Milky Way. The “WHO” in the star’s name comes from the initials of its discoverers - Westerlund, Olander and Hedin; and “G64” indicates that it is the 64th entry in the catalogue published in 1981. The physical properties of WOH G64 are extreme. The star has a relatively cool surface temperature of 3,400 K, but it shines roughly 300,000 times more brightly than does the Sun. With that, WOH G64 is estimated to be 1,540 times larger in size than the Sun, making it one of the largest known RSG stars. If placed at the position of the Sun in the Solar System, the surface of WOH G64 would extend almost to the orbit of Saturn.

Observations of WHO G64 made with the Very Large Telescope Interferometer (VLTI) operated by the European Southern Observatory (ESO) in Chile revealed the presence of an enormous and thick disk of gas and dust around the star. The inner edge of the disk is at ~15 stellar radii from WOH G64, about 120 times the distance of Earth from the Sun. The rest of the disk extends far out from WHO G64, reaching almost one light year in total size. Between 3 to 9 solar masses worth of material is estimated to be in the disk of gas and dust. WHO G64 is at an advance stage of its evolution and is experiencing violent, unstable mass loss. WHO G64 started out with ~25 times the Sun’s mass, but it has since lost between one tenth and a third of its original mass. This stellar behemoth is nearing its final fate as a supernova.

- Levesque et al. (2009), “The Physical Properties of the Red Supergiant WOH G64: The Largest Star Known?”, arXiv:0903.2260 [astro-ph.SR]
- Ohnaka et al. (2009), “Spatially resolved dusty torus toward the red supergiant WOH G64 in the Large Magellanic Cloud”, arXiv:0803.3823 [astro-ph]
- Westerlund, Olander & Hedin (1981), “Supergiant and giant M type stars in the Large Magellanic Cloud”, Astronomy & Astrophysics Supplement Series 43: 267-295