Laboratory evidence for an asymmetric accretion structure upon slanted matter impact in young stars

Abstract

Aims. Investigating the process of matter accretion onto forming stars through scaled experiments in the laboratory is important in order to better understand star and planetary system formation and evolution. Such experiments can indeed complement observations by providing access to the processes with spatial and temporal resolution. A previous investigation revealed the existence of a two-component stream: a hot shell surrounding a cooler inner stream. The shell was formed by matter laterally ejected upon impact and refocused by the local magnetic field. That laboratory investigation was limited to normal incidence impacts. However, in young stellar objects, the complex structure of magnetic fields causes variability of the incident angles of the accretion columns. This led us to undertake an investigation, using laboratory plasmas, of the consequence of having a slanted accretion impacting a young star. Methods. Here, we used high power laser interactions and strong magnetic field generation in the laboratory, complemented by numerical simulations, to study the asymmetry induced upon accretion structures when columns of matter impact the surface of young stars with an oblique angle. Results. Compared to the scenario where matter accretes perpendicularly to the star surface, we observe a strongly asymmetric plasma structure, strong lateral ejecta of matter, poor confinement of the accreted material, and reduced heating compared to the normal incidence case. Thus, slanted accretion is a configuration that seems to be capable of inducing perturbations of the chromosphere and hence possibly influencing the level of activity of the corona.

Inferring possible magnetic field strength of accreting inflows in EXor-type objects from scaled laboratory experiments

“…Laboratory plasmas can be produced by a wide variety of means, for example discharges, plasma guns, pinches, or lasers. In a series of previous works (Revet et al 2017;Higginson et al 2017;Burdonov, K. et al 2020), we have already shown that, using high-power lasers coupled to strong external magnetic field, we could generate plasmas that scale to accretion funnels of CTTSs, those that follow magnetic field lines, and that give rise to the standard observed accretion rates.…”

Experimental Study of the Interaction of a Laser Plasma Flow with a Transverse Magnetic Field

“…Along with the evident relation of the performed experiments to laboratory astrophysics [20][21][22][23][24], in particular, to the problems of plasma penetration from the accretion disk to the magnetosphere of stars [23], the observed magnetized plasma structures can be of interest in the context of other applications. Indeed, many schemes of laser-plasma sources of accelerated charged particles and secondary emissions require sharp boundaries between the plasma and free space.…”

“…At the same time, strong external magnetic fields are actively used in physics of high energy densities. Here, the processes of interaction of laser plasma with magnetic fields open up broad options of studying experimentally a wide spectrum of problems, from improving the efficiency of target heating during controlled fusion using a strong external magnetic field [11][12][13][14][15][16] to modeling astrophysical phenomena in the laboratory [17][18][19][20][21][22][23][24]. For example, when accretion of matter to young stars is modeled, one can successfully employ laboratory experiments with the use of high-speed flows of the laser plasma produced by nanosecond laser pulses that impact solid-state targets located in an external magnetic field [20][21][22][23][24].…”

“…One can see that the quantity <N> does not depend on the energy of the laser pulse and is determined by the ratio of the magnetic flux density B0 of the external magnetic field to the initial ion velocity V0. It should be noted that in most experiments performed to study the spread of the laser plasma produced by irradiating solid-state targets with nanosecond laser pulses [17][18][19][20][21][22][23][24], the characteristic values of V0 turn out to be rather close and lying in the range from 100 to 500 km/s, despite the noticeably different parameters of the laser radiation (e.g., its intensity on the target surface changes from I ∼ 10 11 W/cm 2 [17,18] to I ∼ 10 13 -10 14 W/cm 2 [20][21][22][23][24]). Thus, the influence of the magnetic flux density B0 of the external magnetic field on the average plasma density turns out to be determining.…”

Inferring possible magnetic field strength of accreting inflows in EXor-type objects from scaled laboratory experiments

“…Laboratory plasmas can be produced by a wide variety of means, for example discharges, plasma guns, pinches, or lasers. In a series of previous works (Revet et al 2017;Higginson et al 2017;Burdonov et al 2020), we have already shown that, using high-power lasers coupled to strong external magnetic field, we could generate plasmas that scale to accretion funnels of CTTSs, those that follow magnetic field lines, and that give rise to the standard observed accretion rates.…”