spaceSpace and Physics

Rare “Family Portrait” Of Planet-Forming Disks


The 15 images of protoplanetary disks were captured with ESO's Very Large Telescope Interferometer in Chile. Jacques Kluska et al. 2020

Just over a year ago, the world was left speechless by the first-ever image of the event horizon of a black hole. What made this incredible feat achievable was a phenomenon called interferometry – a technology that combines simultaneous observations from two or more telescopes to help piece together a more precise image. Now, using a similar technique, an international team of astronomers have given us a rare look into the inner rims of planet-forming disks located hundreds of light-years away.

Planet-forming, or protoplanetary disks, are rings of gas and dust particles surrounding a newly formed star. Within these disks, colliding dust grains can grow into larger structures that eventually become planets. The inner regions of protoplanetary disks, less 750 million kilometers (466 million miles) from the host star, are where rocky planets, like Earth, are expected to form.


Although astronomers have captured some truly awesome images of these disks before, so far its inner regions have been rather fuzzy.

“In these pictures, the regions close to the star, where rocky planets form, are covered by only few pixels,” Jacques Kluska, the study lead author from KU Leuven, Belgium, said in a statement. “We needed to visualize these details to be able to identify patterns that might betray planet formation and to characterize the properties of the disks.”

To do so, the team, whose work has been published in Astronomy & Astrophysics, turned to the European Southern Observatory (ESO) in Chile. Kluska and his colleagues first combined the light collected by four telescopes that make up ESO’s Very Large Telescope Interferometer (VLTI), using the observatory’s PIONIER instrument, in a technique called infrared interferometry.

But, as those familiar with the Event Horizon Telescope’s work may suspect, this doesn’t exactly deliver the image of the observed source. In order to produce their images, the team then had to mathematically reconstruct the disks and filter out the light of the star they surrounded. Only then were they able to peer in greater detail at 15 different protoplanetary disks.

The protoplanetary disk around the R CrA Star, with Earth's orbit included as a reference. Jacques Kluska et al. 2020  

“Distinguishing details at the scale of the orbits of rocky planets like Earth or Jupiter…is equivalent to being able to see a human on the Moon, or to distinguish a hair at a 10 km distance,” Jean-Philippe Berger, the principal investigator of the study from the Université Grenoble-Alpes, explained. “Infrared interferometry is becoming routinely used to uncover the tiniest details of astronomical objects. Combining this technique with advanced mathematics finally allows us to turn the results of these observations into images.”

From the images, the team have identified brighter and darker patches in the disks, which they suspect may point them towards the processes that can lead to planet formation. One such mechanism they suggest is that these areas represent instabilities in the disk that draw in grains of space dust, which then grow and evolve into a planet.

Further research into these irregularities is on the cards for the team, the researchers say, as well as carrying out more observations to hopefully one day directly witness a rocky planet form within the inner regions of a protoplanetary disk.


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