Gravitational instability in a planet-forming disk.

Area of Science:

• Astronomy and Astrophysics
• Planetary Science

Background:

• Planet formation theories include core accretion and gravitational instability.
• Gravitational instability requires massive circumstellar disks (disk-to-star mass ratio ~1:10) to form planets directly from collapsing fragments.
• Estimating disk mass is challenging, but gas kinematics can reveal disk instability.

Purpose of the Study:

• To present kinematic evidence of gravitational instability in the protoplanetary disk around AB Aurigae.
• To test the hypothesis that gravitational instability can trigger planet formation.

Main Methods:

• Deep observations of 13CO and C18O line emission using the Atacama Large Millimeter/submillimeter Array (ALMA).
• Analysis of disk-velocity structure to detect kinematic signatures of gravitational instability.
• Quantitative comparison of observed kinematics with simulations and analytic models.

Main Results:

• Kinematic evidence for gravitational instability was detected in the AB Aurigae disk.
• Observed velocity structures closely match predictions from theoretical models.
• Inferred disk mass is up to one-third of the stellar mass within a 1″ to 5″ region.

Conclusions:

• The findings support the gravitational instability theory for planet formation.
• The AB Aurigae disk is massive enough to be gravitationally unstable.
• Direct protoplanet formation via disk fragmentation is plausible in such massive disks.