Dust torus around dying supergiant star detected

Berlin, May 28 : Scientists have detected a dust torus around an individual dying supergiant star in our neighbouring galaxy, the Large Magellanic Cloud.

This discovery was made by a team of researchers at the Max Planck Institute for Radio Astronomy (MPIfR) in Bonn and European Southern Observatory (ESO) in Garching near Munich.

The behemoth star has been found to be surrounded by a massive and thick torus of gas and dust, and is most likely experiencing unstable, violent mass loss.

By combining two 8.2m telescopes in Chile as an interferometer, the researchers achieved the resolving power of a 60-m telescope. Geared with such a super-sharp view, they discovered that the dying supergiant star is developing a thick dust torus around it.

"We discovered that the dying supergiant star WOH G64 is surrounded by a thick dust torus which sort of looks like a thick bagel by comparing it with detailed theoretical modeling," said Keiichi Ohnaka from the MPIfR.

The diameter of the supergiant star is as large as the orbit of Saturn in the solar system, while the dimensions of the whole torus are considerably larger.

The inner edge of the torus is at 120 AU (Astronomical Units), with the total size of the torus reaching almost one light year.

The researchers estimated that the star had an initial mass of about 25 times the mass of our sun. But now, the star is shedding material so rapidly that it has already lost 10 - 40% of its initial mass and is speeding toward its final fate as a supernova.

The observations, made with ESO's Very Large Telescope Interferometer, conclude that the gas and dust around the star is arranged in a thick ring, rather than a spherical shell, and the star is thus less hidden than had been assumed.

This implies that the object is in fact half as luminous as previously thought, and thus, less massive.

"The characteristics of the star mean that it may be experiencing a very unstable phase accompanied by heavy mass loss," said Markus Wittkowski from ESO.

"We estimate that the belt of gas and dust that surrounds it contains between 3 and 9 solar masses, which means that the star has already lost between one tenth and a third of its initial mass," he added.

"For the first time we could take a close-up view of an individual star outside our Galaxy, and this is an important first step to understand how dying stars in other galaxies differ from their counterparts in our Milky Way", said Ohnaka.

ANI