Astronomers using the new Atacama Large Millimeter/submillimeter Array (ALMA) in Chile have imaged a dust trap around a young star that’s 400 light-years away from Earth. They believe their findings may pave the way understanding how planets are formed.

According to the scientists, this is the first time that such a dust trap has been clearly observed and modelled. Dubbing the region a ‘comet factory’, the astronomers believe that their research could solve the mystery about how dust particles in discs morph so that they can eventually form comets, planets and other rocky bodies.

Their findings have just been published in the journal Science.

One of the astronomers involved in the study was Dr Vincent Geers from the School of Cosmic Physics at the Dublin Institute for Advanced Studies.

The scientists were using images from the new ALMA telescope, which is based in Chile’s Atacama desert.

The telescope was less than half completed at the time of the their discovery. ALMA became fully operational in March.

"We know that for a planet to form, dust particles in orbit around a star must collide and stick," explained Geers. Under normal conditions, once objects grow to form rocks about one metre across, he said they should spiral in fast and get eaten up by their star.

The new infra-red images of a young star about 400 light-years from Earth appear to reveal something unexpected, however.

Dust trap for forming comets

Led by Nienke van der Marel, a PhD student at Leiden Observatory in The Netherlands, the astronomers found a crescent-shaped cloud of dust to one side of the star, but did not see the symmetrical dust ring they expected.

They were looking at the star Oph-IRS 48 because they had previously seen an interesting dust ring around it.

"At the time, we suggested that an unseen companion star might be causing this ring, but we needed better images and we had to wait for ALMA to get those," explained Geers.

Thanks to the new images, the group of astronomers now think that there is a ‘dust trap’ there.

"We think it’s a region of high pressure, a kind of vortex, where the dust is captured and can stick and grow to form objects as big as maybe a few kilometres across."

According to van der Marel, this dust cloud region is likely to provide the right conditions for particles to grow from millimetre to comet size – hence the term ‘comet factory’.

"What’s really exciting is that we saw this using only part of ALMA. Now that the full telescope array is working, we should be able to see so much more. By finding dust traps orbiting even closer to their star, we may be able to see planets forming," added Geers.