Chilean astronomers discover new clues about massive star formation
ALMA OBSERVATORY/DICYT Astronomers using the ALMA radio telescope detected that the supersonic jet and the accretion disk survives the ultraviolet radiation generated by the birth of a massive star. This discovery refutes existing theories, indicating that ultraviolet radiation from the star would destroy molecular gas and dust, and bringing the first direct detection of ionized gas wind along with a supersonic jet and an accretion disk. The research results were published in The Astrophysical Journal.
Massive stars emit a large amount of ultraviolet radiation that destroys the molecules and dust surrounding the star and creates ionized gas, which in turn impedes the star's growth process. This is why previous theories have suggested that the model of a small star forming from a protoplanetary gas and dust disk isn’t applicable to high mass stars. According to the study published today, dust and molecular gas can survive the destructive effects of ultraviolet radiation that accompanies the birth of a massive star.
The young star that was studied, G345.4938+01.4677, is located in the Scorpius constellation and has a mass 15 times greater than the Sun. This is where scientists made at least three important discoveries. "The first thing we detected is a supersonic stream emerging from the star forming inside the ionized gas region. This suggests that the accretion disk and gas stream are strong enough to survive despite the damage caused by ultraviolet light," explained Andrés Guzmán, the study’s principal researcher and a postdoctoral fellow at the University of Chile.
ALMA's cutting-edge technology enable astronomers to get, for the first time, evidence of the effect of electric fields on the emission of lines of hydrogen. "The detection of this so called Stark effect was possible due to the high density of gas around this star and ALMA's extraordinary sensitivity," said Guido Garay, Director of the Astronomy Department at the University of Chile and a co-author of the study.
"Thanks to the sensitivity and high angular resolution of ALMA we could for the first time detect a rotating disk around a massive star and effects of electric fields on the hydrogen line emission from a jet from the same star", added Lars Nyman, Head of Science Operations at the JAO ALMA Observatory and co-author of the study.
The third major milestone is the discovery of molecular gas and dust rotating around the massive star. This discovery extends the observation of protoplanetary disks to the high mass regime, where the dynamic is dominated by the mass of the disk rather than the mass of the central star. Even though it was estimated that there are 56 solar masses in the disk, compared to 15 solar masses in the central star, the disk's rotation is perfectly aligned with the stream of ionized gas, suggesting that the supersonic gas stream is being accelerated and aligned from an accretion disk.
In the near future, "we expect to find and study more streams associated with these kinds of hyper-compact ionized regions. Without ALMA it would have been impossible to better characterize the accretion in this massive star and determine whether it is part of a binary system," Guzmán concluded.