ALMA sees the violence of starbirth
Sen—Astronomers have obtained a vivid close-up view of material streaming away from a newborn star and have discovered that its jets are even more energetic than previously thought.
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.
Herbig-Haro 46/47 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 the Atacama Large Millimeter/submillimeter Array (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. 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.
Close-up view of Herbig-Haro 46/47. The blue parts at the left are a jet approaching the Earth (blueshifted) and the larger jet on the right is receding (redshifted). Image credit: SO/ALMA (ESO/NAOJ/NRAO)/ H. Arce
The team leader and first author of the new study, Hector 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 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 a previously unknown jet pointing in a totally different direction, 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!"