20 August 2013

Astronomers Observe Unknown Jet stream From Herbig Haro 46/47


Using the Atacama Large Millimeter/submillimeter Array (ALMA), astronomers have observed materials streaming away from Herbig Haro 46/47 and also discovered a previously unknown jet stream of material flowing away in a different direction.

The image above shows jets of material flowing out of a newborn star (orange, green, pink, and purple) located 1400 light years away from Earth. The pink and purple jets have been observed before but the orange and green jets , previously hidden by the surrounding gas and dust, was just discovered by ALMA and shows these streams to be highly energetic.

The Atacama Large Millimeter/submillimeter Array (ALMA) managed to capture this image because of its much shorter wavelength visible light observations from ESO’s New Technology Telescope (NTT) in combination with radio observations.

Herbig-Haros are young stars that occasionally blast off hot gas and other material into space. THese materials are ejected when the star collides with a gas and dust cloud at high speeds. Herbig–Haro objects are generally found in star-forming regions, and several are often seen around a single star, aligned along its rotational axis.

These objects are named after George Herbig and Guillermo Haro who first studied them albeit independently of each other. They studied star formations when they came upon these objects. They both recognized that these objects were a a by-product of the star formation process.

New Jetstream discovered in Herbig Haro 46/47

Astronomers using the Atacama Large Millimeter/submillimeter Array (ALMA) have obtained a vivid close-up view of material streaming away from a newborn star. By looking at the glow coming from carbon monoxide molecules in an object called Herbig-Haro 46/47 they have discovered that its jets are even more energetic than previously thought. The very detailed new images have also revealed a previously unknown jet pointing in a totally different direction.

Young stars are violent objects that eject material at speeds as high as one million kilometres per hour. When this material crashes into the surrounding gas it glows, creating a Herbig-Haro object. A spectacular example is named Herbig-Haro 46/47 and is situated about 1400 light-years from Earth in the southern constellation of Vela (The Sails). This object was the target of a study using ALMA during the Early Science phase, whilst the telescope was still under construction and well before the array was completed.

The new images reveal fine detail in two jets, one coming towards Earth and one moving away. The receding jet was almost invisible in earlier pictures made in visible light, due to obscuration by the dust clouds surrounding the new-born star. ALMA has not only provided much sharper images than earlier facilities but also allowed astronomers to measure how fast the glowing material is moving through space.

These new observations of Herbig-Haro 46/47 revealed that some of the ejected material had velocities much higher than had been measured before. This means the outflowing gas carries much more energy and momentum than previously thought.

Video: Herbig Haro object HH 46 47 in the Constellation Veia

The team leader and first author of the new study, H├ęctor Arce (Yale University, USA) explains that "ALMA's exquisite sensitivity allows the detection of previously unseen features in this source, like this very fast outflow. It also seems to be a textbook example of a simple model where the molecular outflow is generated by a wide-angle wind from the young star."

The observations were obtained in just five hours of ALMA observation time – even though ALMA was still under construction at the time – similar quality observations with other telescopes would have taken ten times longer.

"The detail in the Herbig-Haro 46/47 images is stunning. Perhaps more stunning is the fact that, for these types of observations, we really are still in the early days. In the future ALMA will provide even better images than this in a fraction of the time," adds Stuartt Corder (Joint ALMA Observatory, Chile), a co-author on the new paper.

Diego Mardones (Universidad de Chile), another co-author, emphasises that "this system is similar to most isolated low mass stars during their formation and birth. But it is also unusual because the outflow impacts the cloud directly on one side of the young star and escapes out of the cloud on the other. This makes it an excellent system for studying the impact of the stellar winds on the parent cloud from which the young star is formed."

The sharpness and sensitivity achieved by these ALMA observations also allowed the team to discover an unsuspected outflow component that seems to be coming from a lower mass companion to the young star. This secondary outflow is seen almost at right angles to the principal object and is apparently carving its own hole out of the surrounding cloud.

Arce concludes that "ALMA has made it possible to detect features in the observed outflow much more clearly than previous studies. This shows that there will certainly be many surprises and fascinating discoveries to be made with the full array. ALMA will certainly revolutionise the field of star formation!"

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