For the first time, astronomers have directly observed the boundary between the inner rotating disk and the outer envelope of a young protostar, filling in an important missing piece in our understanding of the preliminary phases of stellar evolution.
The observations were made with the Atacama Large Millimeter-Submillimeter Array (ALMA) which is the most powerful radio telescope, and the largest astronomical project in existence. ALMA observed the baby star named TMC 1A located 450 light years away in the constellation Taurus. TMC 1A is a star still in the process of forming, giving scientists a unique opportunity to study early stellar evolution in a relatively near by target (450-light-years-away is just around the corner on a cosmic scale).
“The disks around young stars are the places where planets will be formed,” said Yusuke Aso, lead-author of a paper published in the Astrophysical Journal. “To understand the formation mechanism of a disk, we need to differentiate the disk from the outer envelope precisely and pinpoint the location of its boundary.”
Taking advantage of ALMAs extreme sensitivity, scientists were able to observe the boundary between the inner rotating disk and the outer envelope with high accuracy for the first time. It’s understood that material from the outer envelope is continuously falling onto the disk, but scientists had previously been unable to actually see the boundary and transition of material.
ALMA was able to precisely measure the different speeds of material surrounding the protostar, allowing researchers to distinguish the protoplanetary disk from the infalling outer dome. They found that the infalling envelope is located 90 astronomical units (AU) from the central mass – about three times longer than the orbit of Neptune. By measuring the speeds of material, they were able to determine the mass of the star, it being about 0.68 times the mass of the Sun. In addition, they found that dust and gas is falling into the star at a much slower speed than originally thought. Astronomers suspect the magnetic field of the young star might be what slowing the gas down.
“We expect that as the baby star grows, the boundary between the disk and the infall region moves outward. We are sure that future ALMA observations will reveal such evolution,” said Aso.
Materials provided by the National Astronomical Observatory of Japan.