Astronomers discover first step toward planet formation
New detailed observations of the young star DG Taurus show that it has a smooth protoplanetary disk without signs of planet formation.
By National Astronomical Observatory of Japan
An image of the radio wave emission strength from the disk around DG Taurus, observed with ALMA. Rings have not yet formed in the disk, suggesting that it is just before planet formation. Credit: ALMA (ESO/NAOJ/NRAO) - S. Ohashi et al.
Astronomers have gotten very good at spotting the signs of planet formation around stars. But for a complete understanding of planet formation, we also need to study examples where planet formation has not yet started. Looking for something and not finding it can be even more difficult than finding it sometimes, but new detailed observations of the young star DG Taurus show that it has a smooth protoplanetary disk without signs of planet formation. This successful non-detection of planet formation may indicate that DG Taurus is on the eve of planet formation.
Planets form in disks of gas and dust, known as protoplanetary disks, around protostars, young stars still in the process of forming. Planet growth is so slow that it’s not possible to watch the evolution as it happens, so astronomers observe many protostars at slightly different stages of planet formation to build up a theoretical understanding.
A smooth protoplanetary disk.
This time an international research team led by Satoshi Ohashi at the National Astronomical Observatory of Japan (NAOJ) used the Atacama Large Millimeter/submillimeter Array (ALMA) to conduct high-resolution observations of a protoplanetary disk around a relatively young protostar, DG Taurus located 410 light-years away in the direction of the constellation Taurus.
The team found that DG Taurus has a smooth protoplanetary disk, without any rings which would indicate that planets are forming. This led the team to believe that DG Taurus system will start forming planets in the future.
Top: Radio wave strength maps of the DG Tau disk at wavelengths of 0.87 mm, 1.3 mm, and 3.1 mm observed with ALMA and polarization strength maps of radio waves scattered by dust at wavelengths of 0.87 mm and 3.1 mm. Bottom: The simulation which provides the best agreement with the above observations.
Credit: ALMA (ESO/NAOJ/NRAO), S. Ohashi et al.
The team found that in this pre-planet-formation stage, the dust grains within 40 AU (about twice the size of the orbit of Uranus in the Solar System) of the central protostar are still small, while beyond this radius the dust grains have started to grow in size, the first step in planet formation. This is contrary to theoretical expectations that planet formation starts in the inner part of the disk.
These results provide surprising new information about the dust distribution and other conditions at the start of planet formation. Future studies of more examples will further improve our understanding of planet formation.
Provided by National Astronomical Observatory of Japan
Reference: Satoshi Ohashi et al. Dust Enrichment and Grain Growth in a Smooth Disk around the DG Tau Protostar Revealed by ALMA Triple Bands Frequency Observations. The Astrophysical Journal (2023). DOI: 10.3847/1538-4357/ace9b9
