We know that stars form from dense clouds of collapsed gas, but how they grow during their infancy is still a matter of debate. Now, however, Japanese researchers have been able to study a star during this mysterious period, and they think they are closer to understanding what’s going on.
Using the Atacama Large Millimeter/submillimeter Array (ALMA), researchers were able to observe the formation of the disk around a baby star, called TMC-1A, that is 0.68 times the mass of the Sun and located 450 light-years from Earth. The system is undergoing an important transition, as the gas is not falling directly onto the star anymore, instead being organized in a proto-planetary disk, which will lead to the formation of planets.
This observation fills an important gap in our understanding of young stellar systems. The findings are published in the Astrophysical Journal.
"The disks around young stars are the places where planets will be formed," said lead author Yusuke Aso in a statement. "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."
Using ALMA, the astronomers were able to identify the active areas around the star. The fast rotating disk extends 13 billion kilometers (8 billion miles) from the star, while material from the original birth cloud (still infalling) are found outside the disk.
"We expect that as the baby star grows, the boundary between the disk and the infall region moves outward," said Aso. "We are sure that future ALMA observations will reveal such evolution."
ALMA is the first instrument that has the sensitivity to observe the tenuous boundary between these two regions with such accuracy, and the team was able to establish a lot of information about the system thanks to these observations. The infalling material from the gas cloud is falling onto the disk with a speed of 1 kilometer (0.6 miles) per second, which corresponds to a mass increase of one Earth's worth of gas every three years.