Scientists find mysterious new 'molecular bubble' in space

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February 11, 2023

It's only the second time that astronomers have discovered such a bubble related to the 'outflow' of material from a developing star

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A three-color map of the bubble's structure. The blue corresponds to hydrogen, the red to carbon monoxide, and the green 250 μm observations.— Duan et al., ApJ, 2023 via Science Alert

More than 450 light-years away, in the centre of a dense cloud of gas and dust, is a recently discovered structure that is the physical representation of a pair of young stars undergoing star formation.

In the Taurus molecular cloud complex, an astronomical team has discovered a bubble at the centre of a stellar nursery known as Barnard 18 that was likely carved out of the surrounding gas when two developing stars therein developed and expanded.

It's only the second time that astronomers have discovered such a bubble related to the "outflow" of material from a developing star. Scientists may be able to understand more about how the environment affects stars as they grow, thanks to the recent discovery.

Chaotic and complex

Star creation is a chaotic and complex process. A dense, chilly cloud made up of tiny dust grains and gases, including hydrogen, is where it all begins.

A chunk of this cloud eventually dissipates in a swirl under the force of its own gravity, absorbing more particles from the surrounding material. Once it has amassed sufficient mass, the resultant pressure and heat produce the hydrogen that gives stars their core.

However, when a young star gathers mass, it lashes out at the area around it. Not all of the material enters the star, some is accelerated along the magnetic field lines of the protostar towards the poles, where it bursts into space as astrophysical jets.Protostars also generate winds that create vast gaps in the cloud from which they emerge.

These outflows are named "feedback", which are thought to be crucial in both stopping protostellar growth and the development of the interstellar medium, the gas and dust that floats around in the voids between stars.

Because molecular clouds are so dense, it is difficult to detect what is happening inside of them when a star forms. Longer wavelengths of light can pass through the cloud, but shorter ones cannot.

The nebula known as Barnard 18 is dark and neither emits nor reflects light. Optical observations show it to be a dark smudge that resembles a gap in space. Therefore, a group of astronomers from the National Astronomical Observatories of the Chinese Academy of Sciences (NAOC) in China went to radio frequencies to look inside the cloud. The team was led by Yan Duan and Di Li.

They examined the carbon monoxide signal, which may be used to identify structures within a gas cloud, using two separate radio telescopes. The Barnard 18 molecular cloud also had signs of a bubble structure.

"Through combined analysis with the Five College Radio Astronomy Observatory (FCRAO) survey of the Taurus molecular cloud, we found an outflow located at the centre of the molecular bubble," said NAOC astronomer Yan Duan, first author of the team's paper published in The Astrophysical Journal.

The Herbig-Haro object known as HH 319, which has already been recognised by astronomers, lives on Barnard 18. These are made when protostellar jets, which are propelled away from their source stars at extremely high speeds, collide with the molecular cloud and induce luminosity.

Li and his team's discovery of HH 319 near the core of the outflow provides information on the bubble's origin.

Calculations by the scientists indicate that activity from the two stars began sculpting the massive bubble in Barnard 18 around 70,000 years ago.

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