Herschel reveals new stars in a stellar cocoon

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This glowing core is the stellar equivalent of an insect’s cocoon. Nestled in the bright centre are two newly forming stars. When they reach maturity they will begin to generate their own energy and shine out across the Universe.

Small, isolated clouds of forming stars are known as Bok Globules after the 20th century astronomer Bart Bok. Back in the 1940s, their identification was an important step towards the realisation that stars form from the condensation of gas clouds in space.

It was not until the Infrared Astronomical Satellite was launched in the 1980s, and the era of space-based infrared astronomy began, that the idea of Bok Globules as stellar cocoons was confirmed.

This was because to optical telescopes the globules appear completely black, as if they were holes in space. The lack of visible light escaping from the clouds prevented astronomers from seeing what was inside.

Looking in the infrared changes all that by revealing colder dust and being able to penetrate much denser regions in the clouds. And, in the realm of infrared space telescope, ESA’s Herschel is in a class of its own. Its sensitivity to long wavelengths and its larger mirror make it better suited to peering into dark clouds than anything before.

Inside this particular globule, catalogued as CB 244, Herschel has revealed two regions where individual stars will form. In the first, there is a stellar embryo with a temperature of just –255°C. In the second, the temperature is even lower, measured at just –262°C, and there is not even a star yet, only a collapsing core of gas and dust.

The Herschel maps have allowed astronomers to calculate the temperature and amount of matter inside the cloud. The young star contains 1.6 times the mass of the Sun, the collapsing region contains between three and seven times the Sun’s mass. Overall, the cloud is between 10 and 20 times the Sun’s mass, so almost half of it is involved in forming these two stars.

In the future, these stars could become some of the brightest in the whole Galaxy, shining with surface temperatures of thousands of degrees. But for now the two stellar embryos slumber on, growing as they feed on the matter in the surrounding globule.

ESA/PACS & SPIRE Consortium, Amélia Stutz, Max-Planck-Institut für Astronomie.

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