Discovery sheds light on star formation

Observing a newborn star, a team of astronomers, led by Yale University associate professor of astronomy Héctor Arce, discovered twin jets of surprisingly forceful “winds” of carbon monoxide, which could help refine the understanding of stars’ origins and how they shape their emerging stellar systems.

The results of this research were reported in the Astrophysics Journal on Aug. 20. Using the Atacama Large Millimeter/submillimeter Array (ALMA) telescope, the scientists have obtained a vivid close-up view of materials streaming away from a young star. By closely scrutinizing the telescope images of a young stellar object named Herbig-Haro 46/47, researchers were able to spot a previously unknown second jet in a new direction, and through analyzing the glow of the star’s carbon monoxide molecules, they discovered that the carbon monoxide jets were much more energetic than previously thought.

“With accurate and clear images from ALMA, we realize that the outflows from the protostar are much more powerful than we anticipated them to be,” Arce said. “This is crucial because [protostars] can power outflows that interact with the surrounding cloud, which in turn may affect how long it takes and how much material there can be for the star to form.”

Newborn stars grow in mass by drawing in material from the surrounding disk of dust and gas, Arce said. This material passes through the disk surrounding the protostar, or new star, before falling onto the forming star. A portion of this material, however, ends up diverted into the star’s magnetic fields and later spews out as jets from the stars’ two magnetic poles. Since there is a direct relationship between the jets’ velocities and the volume of a star’s accretion disk, studying the jets can shed light on the origins of stars.

Arce’s team is the first to observe both an inward and an outward molecular jet in a protostar. The research team was able to spot a second outflow, hidden in very wide-angled winds. University of Chile astronomy professor Diego Mardones, a co-author of the paper, said the outflow impacts the stellar cloud directly, entering from one side and escaping through another. “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,” Mardones added.

These new observations also suggest that there have been episodes of outflow followed by quieter, less active periods — stars do not form in one continuous accretion of materials, but rather gain dusts and gases in alternating fast and slow periods. Since HH 46/47 is a “typical” stellar body, the research team hopes it will shed light on the formation of the solar system from its infant stages.

The results also provide some interesting insights into planetary formation. Yale astronomy professor Jeff Kenney said stronger molecular outflows at higher velocities imply that star formation is less efficient than presumed. According to Kenney, dramatically powerful jets at high velocity push out the dust and gas, leaving less to form stars and planets.

Though the ALMA telescope — one of the most accurate and powerful in the world — was crucial for the study’s data collection, only a small proportion of the antennae was functioning when the team conducted its research earlier this year.

Once all antennae at ALMA are fully functioning, observation time can be drastically reduced, Mardones said, adding that ALMA will be able to observe molecules in more distant, turbulent clouds in finer details. By using ALMA to analyze imagery of elongated structures around the protostar, one may unveil the mystery of star system formation, he said.

“There is no limit as to what we can do next,” Arce said. “We can observe stars at many different evolutionary stages, in order to combine a study to see how the materials around the stars are forming and evolving. The results will be extraordinary, and nothing like we’ve ever seen before.”

ALMA was established in 2011 and became fully operational in March.

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