Formation and survivability of giant planets on wide orbits

TL;DR

This paper proposes a new mechanism for forming giant planets on wide orbits through disk fragmentation during star formation, emphasizing the importance of late-phase fragmentation and disk conditions.

Contribution

It introduces a model where giant planets on wide orbits form from late-stage disk fragmentation in the embedded phase of star formation, considering the effects of cloud core properties.

Findings

Extended disks can produce giant planets on wide orbits.

Late fragmentation episodes lead to survivable giant planets.

Cloud core mass and angular momentum are critical for formation.

Abstract

Motivated by the recent discovery of massive planets on wide orbits, we present a mechanism for the formation of such planets via disk fragmentation in the embedded phase of star formation. In this phase, the forming disk intensively accretes matter from the natal cloud core and undergoes several fragmentation episodes. However, most fragments are either destroyed or driven into the innermost regions (and probably onto the star) due to angular momentum exchange with spiral arms, leading to multiple FU-Ori-like bursts and disk expansion. Fragments that are sufficiently massive and form in the late embedded phase (when the disk conditions are less extreme) may open a gap and evolve into giant planets on typical orbits of several tens to several hundreds of AU. For this mechanism to work, the natal cloud core must have sufficient mass and angular momentum to trigger the burst mode and also form extended disks of the order of several hundreds of AU. When mass loading from the natal cloud core diminishes and the main fragmentation phase ends, such extended disks undergo a transient episode of contraction and density increase, during which they may give birth to a last and survivable set of giant planets on wide and relatively stable orbits.