From astrobites: “Protoplanetary Disks Might Be More Turbulent than Thought”

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Artist’s illustration of a turbulent protoplanetary disk surrounding a young star. [NASA/CXC/M.Weiss]

Title: The Effects of Protostellar Disk Turbulence on CO Emission Lines: A Comparison Study of Disks With Constant CO Abundance vs. Chemically Evolving Disks
Authors: Mo (Emma) Yu, Neal Evans, Sarah Dodson-Robinson, Karen Willacy, Neal Turner
First Author’s Institution: University of Texas at Austin

Status: Accepted to ApJ, open access

We know it happens. We see that protoplanetary disks — the birthplace of planets — spill the gaseous material at their inner edge onto the young stars around which they orbit. This process of accretion persists throughout the disk’s lifetime and within 1 to 5 million years (or 10 Myr in rare cases), a disk will feed all of its gas to its star and completely fade away — leaving behind only the planets that formed along the way and any leftover rocky material that remains.

The rate at which accretion occurs — as well as why accretion occurs — are both driving forces behind determining what types of planets can form quickly enough in a protoplanetary disk’s relatively short lifetime. While we can measure accretion rates onto stars directly, we still do not know why disks accrete! This is one of the most important unsolved problems in planet formation. Until we can solve it, our models for planet formation are incomplete.

There are two leading potential explanations for why accretion occurs: (1) turbulence, and (2) magnetic winds. In the last two years, several attempts have been made to measure turbulence in a nearby disk for the first time using CO (carbon monoxide) spectral lines. These measurements showed that the turbulence in that system is not strong enough to be responsible for accretion, winning favor for the other idea of magnetic winds.

However, today’s paper led by Emma Yu argues that those measurements were not interpreted properly since they did not take into account the relatively rapid rate at which CO depletes over time (see Figure 1). This paper asks: What can we really learn about turbulence from CO spectral lines if we include CO depletion in our model?

See the full article here .

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