ALMA sees the violent birth of stellar twins

ALMA sees the violent birth of stellar twins

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Japanese astronomers have used ALMA to witness the birth of a star in close-up. To their surprise, it turns out to be a chaotic, violent process – not something calm and quiet as most astronomers had thought. Moreover, they accidentally discovered that the star appears to be the first-born of a binary star.

A binary star consists of two stars orbiting each other. Just like human twins, the stars in a binary have the same age. But they are not born at exactly the same moment. Again, that’s just like twin brothers or sisters: one of the twins is always slightly older than the other.


Stars are born in dense clouds of gas and dust. To see these newly born ‘proto-stars’, you need a big telescope like ALMA. By observing at millimeter and submillimeter wavelengths, ALMA can peer through the dust and reveal the baby stars inside. Thus, the Japanese astronomers studied a known proto-star at a distance of 450 light-years in the constellation Taurus, the Bull.

They had expected to see a slowly contracting cloud of gas. Instead, what they saw was a turbulent scene of inflows and outflows, dense patches, and curved ‘tails’ of gas, tens of billions of kilometers long.

From studying the outflows, the astronomers conclude that the proto-star is no older than 200 years, and maybe even much younger – extremely young in astronomical terms. What’s more: the star appears to be the first-born ‘sister’ of a stellar twin.

How do the astronomers know? Well, close to the baby star, ALMA discovered a cloud of gas that has been strongly drawn together by its own gravity. The density of this small gas cloud is so high that it won’t be long before it will also turn into a proto-star. So the end result will be a binary star.

The new ALMA observations will teach astronomers a lot about the birth of binary stars. It is like walking into a nursery where a mother is giving birth to twins, just after the birth of the older child and just before the birth of its younger sibling – what more could you ask for?

The star-forming region studied by the Japanese astronomers is known as MC27/L1521F. It is located in the constellation Taurus (the Bull), at a distance of 450 light-years. It’s actually one of the closest star-forming regions known; that’s why ALMA could see so much detail.

The observations were carried out by a large Japanese team, led by graduate student Kazuki Tokuda and professor Toshikazu Onishi, both at the Osaka Prefecture University. The new results have been published in the 11 June issue of Astrophysical Journal Letters.