Flows of gas through a protoplanetary gap

Observations of the young star HD 142527, whose disk is separated into inner and outer regions by a gap suggestive of the formation of a gaseous giant planet, show that accretion onto the star is maintained by a flow of gas across the gap, in agreement with dynamical models of planet formation. Gas giants leave their mark According to current theories, giant planet formation carves a deep gap in the gas and dust around a protostar, clearing most of the dust and some of the gas away to form a ring-shaped cavity. But such a gap would rapidly turn off further growth in the mass of the star unless the abundant gas from the outer disk could traverse it. This paper presents Atacama Large Millimeter/submillimeter Array observations of the disk around the young star HD 142527 that reveal diffuse CO inside the gap and denser HCO + gas along gap-crossing filaments. The estimated gas flow across the gap would be sufficient to maintain accretion onto the star at the present rate. The formation of gaseous giant planets is thought to occur in the first few million years after stellar birth. Models 1 predict that the process produces a deep gap in the dust component (shallower in the gas 2 , 3 , 4 ). Infrared observations of the disk around the young star HD 142527 (at a distance of about 140 parsecs from Earth) found an inner disk about 10 astronomical units ( au ) in radius 5 (1 au is the Earth–Sun distance), surrounded by a particularly large gap 6 and a disrupted 7 outer disk beyond 140 au . This disruption is indicative of a perturbing planetary-mass body at about 90 au . Radio observations 8 , 9 indicate that the bulk mass is molecular and lies in the outer disk, whose continuum emission has a horseshoe morphology 8 . The high stellar accretion rate 10 would deplete the inner disk 11 in less than one year, and to sustain the observed accretion matter must therefore flow from the outer disk and cross the gap. In dynamical models, the putative protoplanets channel outer-disk material into gap-crossing bridges that feed stellar accretion through the inner disk 12 . Here we report observations of diffuse CO gas inside the gap, with denser HCO + gas along gap-crossing filaments. The estimated flow rate of the gas is in the range of 7 × 10 −9 to 2 × 10 −7 solar masses per year, which is sufficient to maintain accretion onto the star at the present rate.