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Planet formation in action
Posted: 28 February 2011

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Using ESO’s Very Large Telescope, astronomers may have detected the first object clearing its path in the dusty, short-lived disc surrounding a young star.

The international team of astronomers studied a faint star 350 light years from Earth called T Chamaeleontis (T Cha), which is a very young star at some seven million years old, still heading towards becoming a sun like our own. Surrounding the young star, like many others of a similar age, is a disc of material that could spawn planets. While planets have been seen in the more mature discs of other stars (e.g. 12 million year old Beta Pictoris, read more here), until now, none had been identified in this early phase of disc evolution.

Artist impression of the dusty disc around T Cha. A companion object, seen in the foreground, has been detected in the gap in the disc. The inner dust disc is lost in the glare of the star on this picture. Image: ESO/L. Calçada.

“Earlier studies had shown that T Cha was an excellent target for studying how planetary systems form,” says Johan Olofsson of the Max Planck Institute for Astronomy. “But this star is quite distant and the full power of the Very Large Telescope Interferometer (VLTI) was needed to resolve very fine details and see what is going on in the dust disc.”

Using the AMBER instrument and VLT Interferometer to combine light from all four of the 8.2-metre telescopes, the team were able to resolve a narrow dusty ring only 20 million kilometres from the star. Beyond this inner disc lay a region devoid of dust, with the outer disc extending out to more than 1.1 billion kilometres from the star.

This visible-light wide-field image of the region around the young star T Cha was created from photographs taken through red and blue filters and forming part of the Digitized Sky Survey 2. The star appears close to the centre. Some of the dust associated with this star-forming region is faintly visible in the background, particularly at the upper left. Image: ESO and Digitized Sky Survey 2 and Davide De Martin.

“For us the gap in the dust disc around T Cha was a smoking gun, and we asked ourselves: could we be witnessing a companion digging a gap inside its protoplanetary disc?” asks Nuria Huelamo of the Centro de Astrobiologia in Spain.

Further investigation using the VLT’s adaptive optics instrument NACO to remove the blur of Earth’s atmosphere, enabled the astronomers to home in on object located in the gap about one billion kilometres from the star – close to the outer edge of the gap at roughly the same distance Jupiter is from our own Sun. The object is much smaller than the star and is likely either a brown dwarf or a recently formed planet. Future observations will enable the astronomers to reach their conclusions, and to learn more about the behaviour and characteristics of the discs in young stellar systems.