Munich, Sept 28 : The European Southern Observatory’s (ESO’s) Very Large Telescope (VLT) Interferometer has helped astronomers discover a reservoir of dust trapped in a disc that surrounds an elderly star.

Scientists say the discovery provides additional clues about the shaping of planetary nebulae.

In the last phases of their life, stars such as our Sun evolve from a red giant, which would engulf the orbit of Mars to a white dwarf, an object that is barely larger than the Earth.

The transition is accomplished by the shedding of a huge envelope of gas and dust that sparkles in many colours, producing a most spectacular object: a planetary nebula.

However, this metamorphosis, rapid in terms of the star's lifetime, is rather complex and poorly understood.

In particular, astronomers want to understand how a spherical star can produce a great variety of planetary nebulae, some with very asymmetrical shapes.

Now, a team led by Pieter Deroo have embarked upon the study of a star, which is presently on its way to becoming a cosmic butterfly.

The star, V390 Velorum, is 5000 times as bright as our Sun and is located 2,600 light-years away. It is also known to have a companion that takes 500 days to make one revolution around it.

Astronomers postulate that elderly stars with companions possess a reservoir of dust that is thought to play a lead role in the final chapters of their lives. The shape and structure of these reservoirs, however, remain largely unknown.

To scrutinise the object with great precision, the astronomers linked observations taken with ESO's VLT I, AMBER and MIDI, at the Very Large Telescope Interferometer.

In particular, they combined, using AMBER, the near-infrared light of three of VLT's 8.2-m Unit Telescopes.

“Only this triple combination of powerful telescopes allows us to pinpoint the position and the shape of the dusty reservoir on a milli-arcsecond scale,” said Deroo, lead-author of the study in the journal Astronomy and Astrophysics.

The observations revealed that the dust present around the star couldn’t be distributed in a spherical shell.

"This shows that whatever mechanism is shaping asymmetric planetary nebulae is already present prior to the metamorphosis taking place,” said team member Hans Van Winckel.

Further observations revealed the evidence of a disc extending from 9 Astronomical Units to several hundreds of AU.

“This disc is found around a star that is in a very brief phase of its life - just a blink of an eye over the star's lifespan of billions of years - but this phase is very important,” said Deroo.

“It is in this period that a huge morphological change occurs, leading to the creation of a planetary nebula,” he added. (With inputs from ANI)