Accretion funnels connecting the young stars in Orion and their protoplanetary disks. The study “X-Ray Flare Oscillations Track Plasma Sloshing along Star-disk Magnetic Tubes in the Orion Star-forming Region” of F. Reale published on ApJ
di Mario Giuseppe Guarcello ( segui @mguarce)
A recent study by a team of researchers of INAF-Astronomical Observatory of Palermo, the University of Palermo, and the University of Madrid, recently published on the Astrophysical Journal, shows that enormous flares in the young stars in Orion are due to large magnetic loops connecting the stars and their protoplanetary disks, confining plasma oscillating from disk to the star.
Stars form for the gravitational collapse of molecular clouds. One of the remnant of the collapsing cloud is a protoplanetary disk orbiting around young stars. Disks are dispersed by several mechanisms, mainly driven by the radiation of the central star itself, and for the first few million of years they can accrete material onto the central star thanks to magnetic funnels connecting star and disk. There are evidence, in fact, that rapidly rotating young stars can support such large magnetic structures.
Solar magnetic field is order of magnitude less intense than that of young stars. However, it causes spectacular phenomena such as coronal flares, visible in X-rays and UV. During flares, the emitting region can be brighter in X-rays than the whole solar corona and the it contains plasma heated up to tens of million degrees.
Such magnetic structures exist in young stars as well and they can produce flares thousands times brighter in X-rays than their solar counterparts, with plasma reaching a temperature exceeding 100 million of degree. These flares are typically observed in star forming regions and, in fact, young stars are often identified by means of their large X-ray emission. Besides, flares occurring in young stars can last for days, while solar flares typically last from few minutes to few hours.
The Orion Molecular Cloud contains thousands of young stars. It has been recently observed in X-rays with the NASA satellite Chandra as part of the “Chandra Orion Ultradeep Project”, in which the Observatory of Palermo has been heavily involved. During the observation, several X-ray flares have been observed, and some of them show oscillations in their X-ray emission with a period of several hours.
The team of researchers led by F. Reale, of the Astronomical Observatory and University of Palermo, have simulated the phenomenon causing such bright X-ray flares in young stars with very long oscillations. They have shown that these flares are due to magnetic loops long several stellar radii and connecting star and their protoplanetary disks, confining very hot plasma which oscillates from the disk to the star. “It has been long debated whether such long loops exist” — F. Reale says — “and our simulations provides strong evidence that they actually exists. It is in fact difficult to imagine that such a long and coherent behavior could be generated in small loops which are ignited simultaneously. Our model instead reproduces the observed oscillations of X-ray emission naturally. It is also interesting to note that such bright flares can have a strong impact on the environment where planets form.”
The figure (link) shows a magnetic loop connecting a young star with its protoplanetary disk, confining hot plasma which is oscillating from the star to the disk