Dust traps could be a key element in planet formation

Protoplanetary disk with a dust trap seen as a bright ring (Image courtesy Jean-Francois Gonzalez)
Protoplanetary disk with a dust trap seen as a bright ring (Image courtesy Jean-Francois Gonzalez)

An article published in the journal “Monthly Notices of the Royal Astronomical Society” describes a research that provides an explanation for one of the last remaining mysteries about planet formation. An international team of researchers conducted a series of simulations that show that in the protoplanetary disk around a young star dust traps form that accelerate the aggregation of pebble-sized fragments from which planets are born.

The planetary systems form from disks of gas and dust around very young stars. Now astronomers have studied several examples of planetary formation in various stages that helped to improve the models that describe this phenomenon but not all stages are fully explained yet. In particular, there were problems in explaining how pebbles can aggregate to reach the next stage of planetary formation.

A team led by Jean-Francois Gonzalez of the Centre de Recherche Astrophysique de Lyon, France, tried to study the problem and figure out how to overcome what seem big obstacles. One is the fact that in the protoplanetary disk the star’s gravitational pull threatens to devour the available materials and the other from the danger that high-speed collisions among pebbles destroy them.

These problems can be avoided in what are called dust traps, regions where the pressure is high and dust particles can aggregate to form larger bodies that become the blocks from which the planets are born. In those regions the speed of the grains is reduced and this allows to avoid high-speed collisions that could destroy them.

Until now, astronomers thought that dust traps could exist only in very specific environments but the computer simulations conducted in the course of this new research indicates that on the contrary are very common. A key element is given by the interaction between dust and gas. In most of the simulations, the gas causes the dust movement but sometimes, in the most dusty regions, that dust acts with greater force on the gas.

The dust particles are slowed down and have more time to grow to the point where they are no longer influenced by the gas. At that point the gas is pushed outwards and form a high pressure region: the dust trap. In this region the grains that come from the outer regions of the protoplanetary disk end up concentrating increasing the size of the fragments and helping the formation of increasingly large bodies.

These are the results of simulations but if you really dust traps are common it finding them shouldn’t be so difficult. Various groups of researchers have already started looking for them using instruments such as the ALMA radio telescope. In recent years several newborn solar systems were found so there are already candidates with bright and dark rings where there may be dust traps.

Stages of the formation mechanism for dust traps (Image courtesy Volker Schurbert)
Stages of the formation mechanism for dust traps (Image courtesy Volker Schurbert)

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