In the News this month: spectacular outflows in Orion
Artist's conception of the "boiling disk" surrounding the massive young stellar object known as Orion Source ICREDIT: Bill Saxton, NRAO/AUI/NSF
The constellation of Orion contains some massive complex regions of star formation, the most obvious of which is the Great Orion Nebula, M42, located in Orion's sword. Through an optical telescope you can see a large glowing cloud of gas illuminated by a cluster of young, hot stars. But behind this cloud, hidden from view, lies another cluster of proto-stars, clumps of gas still collapsing under gravity in the process of forming stars. As ordinary light cannot penetrate through the gas, other parts of the electromagnetic spectrum are needed to see these proto-stars. Luckily, radio waves can penetrate through the thick gas and dust and can provide images of these stars in the process of formation. Using the Very Long Baseline Array, a collection of ten radio telescopes located across the USA, a team of astronomers has peered into this hidden region and imaged it at high resolution.
The team, led by Lynn Matthews at MIT's Haystack Observatory, used the VLBA to study an object known as source I over two years. This source lies at a distance of just 414 parsecs, making it the closest known example of the class known as Young Stellar Objects. The astronomers used the VLBA to make regular monthly images over two years, studying the motion of sources known as masers, naturally occurring objects which act like lasers but at radio wavelengths. The images show thousands of silicon monoxide masers in outflows from the proto-star known as source I, and by stitching together all of the images taken over two years, the team produced a movie showing the outflows of molecular material between 20 and 100 astronomical units from the young star in unprecedented detail.
It is already known how these massive stars die - they explode catastrophically as supernovae - but how they form is more of a mystery since the formation process takes place inside a thick cloud of gas. These observations show signs of a rotating accretion disk around the proto-star, drawing surrounding material in a spiral motion towards the centre where the new star is still growing. They also show material flowing out from the centre, perpendicular to the disk, in two large cones, one above and one below the disk. Outflows like these help the star formation process by carrying angular momentum away from the system, if a protostar spun too quickly it might start losing material and ultimately rip itself apart. The movie also shows the outflows starting to curve as they leave the accretion disk, suggesting that magnetic fields may be influencing the motion of material near to the star. The paper describing this work has been accepted for publication in the Astrophysical Journal in January 2010.
L. D. Matthews, L. J. Greenhill, C. Goddi, C. J. Chandler, E. M. L. Humphreys, & M. Kunz (2009). A Feature Movie of SiO Emission 20-100 AU from the Massive Young Stellar Object Orion Source I Astrophysical Journal arXiv: 0911.2473v1