Understanding the mechanisms of formation for high-mass stars (more than 8 times the mass of the Sun) is one of the great enigmas of modern astrophysics. While the mechanisms for smaller stars appear clear and well-documented through observations, the situation is different for massive stars, omega replica watches which are generally too distant, rapidly evolving, and have too high energy.
One hypothesis proposed by some researchers, not yet supported by observational data, is that gas jets emitted from the center of the accretion disk surrounding the protostar, in combination with the magnetic field, may significantly aid star formation more than they do during the formation of smaller stars. In fact, only through these jets is it possible to reduce the pressure generated by the radiation emitted by the forming protostar, allowing further accretion of the protostar itself until it reaches its enormous final mass.
A step forward in this field is reported in the article just published in Science by an international team that includes two Sardinian astronomers, Gabriele Surcis from the Joint Institute for VLBI in Europe (JIVE), and Ciriaco Goddi from Radboud University Nijmegen.
The article presents two images of the star W75N(B)-VLA2, located about 4,200 light-years from Earth, taken 18 years apart with the Karl G. Jansky Very Large Array (VLA).
The figure shows an artistic representation of the evolution of the gas jet expelled by the protostar, on the left as observed in 1996 and on the right its current morphology.
Image Credit: Wolfgang Steffen, Instituto de Astronomía, UNAM
The spectacular difference between the two images (see the animation produced by JIVE) shows the evident evolution of the gas jet emitted by the protostar interacting with the dense dust torus surrounding it.
“The surprising thing,” says Gabriele Surcis, “is that we observed the change in its collimation over an 18-year timescale. It’s a bit like watching a newborn’s first blink from kilometers away.”
Furthermore, Ciriaco Goddi adds: “The observed evolution shows an impressive agreement with existing theoretical models, which predict a much more spherical expansion of jets than one would expect based on observations of lower-mass stars.” “An even more interesting aspect,” adds Surcis, “is that we also observed a variation in the magnetic field, in line with the evolution of the jet, indicating that matter is expelled along the magnetic field as predicted by the latest simulations.”
A discovery that certainly represents an important first step towards understanding the formation of massive stars.
“Of course, we will continue to monitor the protostar with various projects,” concludes Surcis. “One of these will last 6 years, and we will use the European VLBI Network, of which the Sardinia Radio Telescope is now an active part.”
Good luck to the entire team, especially to our former colleagues and fellow students!
Read the JIVE press release
Read the news on Media INAF
Gabriele Surcis graduated in Physics in Cagliari, with a thesis developed at the extragalactic radio astronomy group of the Cagliari Observatory. After obtaining his PhD at the Angerlander-institut fuer Astronomie in Bonn, he took on the role of Support Scientist at the “Joint Institute for VLBI in Europe,” the European center
for European radio interferometry, where he still works.
Ciriaco Goddi earned his degree and PhD in Physics in Cagliari, with a thesis developed at the interstellar medium astrophysics group of the Cagliari Observatory. After various post-docs in Italy (at the Arcetri Observatory in Florence) and abroad (at the Harvard-Smithsonian Center for Astrophysics, the European Southern Observatory), he was a Support Scientist at the “Joint Institute for VLBI in Europe.” He currently holds the position of Project Scientist for the BlackHoleCam project at Radboud University in Nijmegen, Netherlands.