For the first time, the “placenta” of a star baby

is accurately measured.

For the first time, the “placenta” of a star baby

It is well known that when a massive cloud of gas is destroyed by its own gravity, a star child may form. Intensive gravitational collapse begins to customize the processes of merging, splicing more matter, and this feeds the newborn star. Although the overall process is well studied, but the details are still not considered.

For example, a star embryo growing inside a gas cloud does not “feed” directly from the same cloud. Regardless of the cloud, the spirals of the child star create a fast swirling hot disk. Thus, the star is fed by a disk, which in itself is fed by gas from the surrounding cloud. This disc acts almost like a placenta mother. It is not the mother itself, but the placenta, which provides nutrients for the developing embryo.

But astronomers could not accurately determine where the disc ends around the newborn star (“placenta”) and where the inner boundary of the gas cloud (“mother”) begins. Now, astronomers using the Atakam Large (Antenna) Millimeter Range Lattice (ALMA) have seen this boundary through direct observation, which will undoubtedly improve stellar (and planetary) modeling. “The discs around the stars are the places where planets will be formed,” said Yusuke Aso of the University of Tokyo and lead author of an article published in the Astrophysical Journal (Astrophysical Journal). “In order to understand the disk formation mechanism, it is necessary to differentiate the disk from the outer shell and accurately determine the location of its border.”

Optically enlarging a protostar called TMC-1A, located about 450 light years from Earth in the constellation Taurus, the Aso team was able to see its internal rotating disk (planetary disk) and differentiated it from the cloud feeding it. For this study, ALMA's extreme accuracy in measuring velocity distribution played a significant role.

In the case of TMC-1A, the transition boundary from a rotating disk to the surrounding gas envelope was measured at 90 a. e. (astronomical units, where 1 a.e. equals the average distance of the Earth's rotation around the Sun) from the central children's star. This distance is three times greater than orbit of Neptune. Moreover, ALMA's observations showed that the protostar disk obeys Kepler's movement. That is, the star closest to the orbit moves faster, while the additional material from the orbit moves more slowly. This is important: using the speed of rotation of the gas in the disk, the researchers were able to calculate the mass of the children's star. This “star child” weighs about 0.68 (68% or about two three) the mass of our Sun. In addition, they were able to bring the speed at which matter falls from disk to a star - one millionth of our Sun's mass falls in TMC-1A every year at a speed of 1 kilometer per second.

Interestingly, this mass in the fall develops a much lower speed than could be expected if the gas fell at the speed of free fall (that is, nothing prevents the flow).

“We expect that as the child star grows, the boundary between the disk and the precipitation area will move outwards,” said Aso. “We are confident that future ALMA observations will show such an evolution.”

Thus, astronomers have taken interstellar ultrasound of a star, which is in the process of growing inside its star room, revealing unprecedented details on how protostar stars are formed.

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