With the help of the ALMA array, an international team of scientists was able to find an incredibly small accretion disk around one of the youngest protostars. This discovery establishes a new time limit on the theory of disk formation, pushing the dates a few periods earlier. We also managed to fix a compact rotating outflow that can track the disk wind, transferring angular momentum from the disk and facilitating the formation process.
A jet, a disk and an outflow in the protostar HH 211 system. Above: a composite image showing the jet system. Bottom: Increasing the innermost region around the central protostar, showing the disc and outflow. Asterisks indicate the possible location of the central protostar. Gray arrows show the axis of the jet. Orange displays a dusty disc at a submillimeter wavelength in the ALMA overview.
ALMA is such a powerful tool that it managed to resolve an accretion disk with a radius of up to 15 a. e. It is several times younger than the one found earlier, so the result provided a more precise time limit on the theory of disk formation. In addition, this is a plus for a model where the radius of a disk grows linearly with the protostellar mass, and supports the scenario of early onset and slow growth versus the scenario of slow onset and rapid growth. HH 211 is one of the youngest stars in the Perseus system, distant by 770 light years. The central protostar is about 10,000 years old, and its mass is 0.05 solar. It controls a powerful bipolar jet and should effectively absorb the material.
Size comparison between the HH 211 disk (left) and the HH 211 disk (right). Please note that the disc of the first star was turned specially to simplify the comparison procedure
Previous search with a resolution of 50 a. e. showed only a small dust disk around the protostar. Now with an ALMA resolution of 7 a. e. visibility improved when viewed at submillimeter wavelength. He was not only discovered, but also allowed. It is almost an extreme accretion disk feeding the central protostar with a radius of 15 a. e. It is dense, which means that submillimeter light-emitting grains do not yet settle on the middle plane. They also managed to notice a compact rotating outflow that can trace the disk wind carrying angular momentum from the disk, which facilitates the formation process.
These observations allow you to directly detect and characterize tiny disks around the youngest protostar with high resolution ALMA.
