Jets Spiral in 'Reverse Whirlpool' from Star
This artist's concept shows the protostar HH 211, as it accretes material from a surrounding disk. Some of the material from the disk is ejected outward in a bipolar jet. The matter in the jet rotates around the jet's axis, carrying away angular momentum so the star can grow.
Credit: Change Tsai (ASIAA)

Astronomers have observed for the first time a jet of matter spiraling outward from an infant star, as if a lengthy strand of curly pasta.

The enormous jet, which shoots out in two directions, is rocketing material away from the so-called protostar and into interstellar space at more than "supersonic speeds." From end to end, the bipolar jet extends 16,000 astronomical units (AU), where 1 AU is the average distance between the Earth and sun.

Called Herbig-Haro (HH) 211, the protostar is located about 1,000 light-years away in the constellation Perseus. Scientists have estimated HH 211 started gathering stellar material about 20,000 or so years ago.

"It's like an infant compared to the sun," said astronomer Qizhou Zhang of the Harvard-Smithsonian Center for Astrophysics in Cambridge, Mass. "Ultimately this object we observed will grow into a star like the sun, but right now it's only 6 percent of the mass of the sun."

The finding, detailed in the Dec. 1 issue of the Astrophysical Journal, confirms a key step of star formation, one that astronomers have suspected since the 1980s.

Stellar birth

Stars are thought to form at the center of rotating disks of hydrogen gas and dust. Over time, protostars pack on material from spinning disks, meanwhile getting hotter and hotter, until they begin nuclear fusion. This hydrogen-burning process keeps full-blown stars aglow.

However, there's a stellar glitch of sorts. Similar to dizzying rides that rotate so swiftly riders stick to the outer walls, as a disk rotates faster and faster, the swirling matter sticks to the disk's outer edge. The gas can't fall inward toward the star until it sheds excess spin power called angular momentum.

"It has to get rid of the spin energy otherwise the matter will just keep swirling around in this disk around the star without actually going into the star," Zhang told SPACE.com.

Reverse whirlpool

Theory suggests nascent stars could shed excess angular momentum in the form of gas spiraling outward around shooting jets. Zhang and his colleagues glimpsed such spiraling gas using the Submillimeter Array (SMA), which consists of eight radio telescopes located atop Mauna Kea in Hawaii.

Measurements showed matter rotating around the jet's axis in a sort of "reverse whirlpool." The results suggest the bipolar jet moves outward at a speed greater than 200,000 mph (322,000 kph), while matter swirls around the jet's major axis at more than 3,000 mph (4,828 kph).

"HH 211 essentially is a ?reverse whirlpool,'" Zhang explained. "Instead of water swirling around and down into a drain, we see gas swirling around and outward."

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