Massive baby star also has rotating jet 
New discoveries

Massive baby star also has rotating jet 

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Here’s the story of the birth of a massive star. It all starts with a huge cloud of gas and dust. The cloud contracts under its own gravity. It gets smaller and denser. It also starts to rotate faster and faster. Due to the rotation, the cloud begins to flatten into a disk. Gas in the center of the cloud further collapses into a star. Meanwhile, two jets of gas are blown into space, in opposite directions. These jets are aligned with the rotational axis of the baby star, so they are perpendicular to the disk. 

Astronomers have seen many protostars like this: they are surrounded by a rotating disk, and they spew jets of gas into space. There’s one problem, though. As it gets smaller and smaller, the contracting cloud of gas is expected to rotate ever faster. Still, most stars eventually end up as slow rotators. So where does all the rotational energy go? 

Using ALMA, astronomers may now have solved this mystery by studying a massive baby star in the Orion Nebula. ALMA’s vision is sharp enough to study the jets of the baby star in detail. ALMA discovered that the jets themselves are also rotating. What’s more, they 

rotate in the same direction as the disk. Apparently, a lot of rotational energy ends up in the two jets. That explains why the newborn star will end up with a slow spin. 

The new ALMA observations also revealed that the jet is more or less hollow, a bit like a garden hose. Moreover, it doesn’t originate at the position of the star, but at the surface of the outer part of the contracting disk. This indicates that the jet is produced by magnetic forces and centrifugal forces. (As the name implies, a centrifugal force is the same force that slings clothes to the wall of a rapidly rotating centrifuge.) Other astronomers also found evidence for rotation in the jets of a more lightweight star. It looks like all baby stars, big and small, have rotating jets. The new findings will help astronomers to better understand the birth of stars – both dwarf stars and giant stars. 


The massive baby star studied by ALMA is known as Orion KL Source I. It lies in the famous Orion Nebula – a huge star-forming region some 1,400 light-years away from Earth. The star will probably end up being a few times more massive than our own Sun. Right now, it is still surrounded by a thick, contracting disk of gas and dust. From Earth, this disk is seen almost edge-on. As a result, ALMA was able to study the two perpendicular jets of gas in much detail. 


The massive baby star Orion KL Source I was observed by Japanese astronomer Tomoya Hirota. Tomoya is an assistant professor at the National Astronomical Observatory of Japan (NAOJ). He worked together with colleagues from Japan, Korea and the Netherlands. The team published their findings in a professional magazine called Nature Astronomy.