ALMA sees how matter spirals into a young baby star

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Do you remember the last time you were on a merry-go-round on a playground or a fair? Because of
the fast rotation, you felt like being pushed outward. It would be very hard to make your way to the
center of the merry-go-round!

The same ‘centrifugal force’ is at play in the universe. Rotating matter tends to be flung away.
Therefore, the growth of newborn stars is a bit of a mystery.

Stars are born from large molecular clouds of gas and dust. As the cloud contracts (because of
gravity), it turns into a flat, spinning disk. At the center of the disk, the new star is eventually born.
But the star can only grow to its final size by attracting ever more gas from the spinning disk. So how
does this gas manage to make its way to the center? After all, the rotation of the disk wants to fling it
away into space, just like the rotating merry-go-round tries to fling you off.

Theorists have come up with a solution. They calculated what might happen if the disk is still being
‘fed’ by gas from the larger molecular cloud. It turned out that the disk would develop a spiral-
shaped pattern. In the whirlpool-like spiral arms, the density of the gas and dust is higher than
average. Along these spiral arms, matter would flow much more easily toward the central star.
Thanks to its extremely sharp vision, ALMA has now imaged this whirlpool pattern for the first time,
in the rotating disk surrounding a newborn baby star. Apparently, the theorists were right! If similar
spiral patterns will be detected around other young baby stars, astronomers may gain a much better
understanding of the formation of stars.

What?

The spiral pattern was detected in the large disk of gas and dust surrounding a young baby star 1,300
light-years away in the constellation Orion. The star is at most half a million years old, which is
extremely young for a star. Its light cannot be seen by normal telescopes, because it is hidden in a
large, dusty molecular cloud. Earlier observations with infrared telescopes have revealed that the
star’s disk is about 50 billion kilometers in diameter. By mapping the feeble submillimeter radiation
from dust particles in the disk, ALMA has now revealed the denser-than-average spiral arms.

Who?

The ALMA observations of the baby star’s disk were carried out by Chin-Fei Lee of the Academia
Sinica Institute of Astronomy and Astrophysics in Taiwan, Zhi-Yun Li of the University of Virginia in
Charlottesville, and Neal Turner of NASA’s Jet Propulsion Laboratory in Pasadena, California. The
three astronomers have published their new findings in Nature Astronomy.

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