JET-CME

Solar dynamic phenomena as an astrophysical laboratory: Jets and Coronal Mass Ejections

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 Obiettivo del progetto (Objective)

'Magnetic fields are produced in differentially rotating and convecting environments, such as in the interior of the sun, other convective stars and also in accretion disks. The produced magnetic fields emerge in the outer atmospheric layers because of magnetic buoyancy producing a plethora of explosive events. This Emergence of Magnetic Flux (EMF) is a fundamental astrophysical phenomenon and the possible driver of the observed, ubiquitous activity in astrophysical plasmas. In the case of the Sun, the Rosette Stone of Astrophysics, EMF is a key process, ultimately linked to the formation of active regions (ARs) at the solar surface (photosphere). Moreover, it is thought that flux emergence contributes considerably to the driving of spectacular phenomena as solar and astrophysical jets, and the Coronal Mass Ejections (CMEs). Therefore, the main aim of this proposal is to understand the coupling between EMF and fundamental aspects of solar/astrophysical dynamic events. Among the related outstanding questions are the nature of jets and the basic physics behind the onset of dynamic eruptions (e.g. CMEs) in regions of EMF. More precisely, in this work we propose to investigate in a self-consistent manner (i) the acceleration mechanism of jets associated with EMF, (ii) their impact on heating the solar corona and driving the solar wind, (iii) the onset of CME-like eruptions, especially when they originate from within sigmoidal regions and (iv) the relation between CMEs, jets and EMF. While the existing observational evidence of the formation of jets and CMEs is phenomenologically consistent with theoretical models, more quantitative agreement is missing and deeper understanding of the processes at work is still elusive. The proposed research will be carried out using state-of-the-art 3D MHD simulations and high-resolution observations with the aim to provide essentially a first-principle investigation of the relevant physics of the phenomena under study.'

Introduzione (Teaser)

Observations have revealed that magnetic fields produced in the interior of the Sun emerge through the photosphere as bundles of magnetic flux. EU-funded scientists studied this phenomenon by means of state-of-the-art computer simulations and shed light on what drives solar eruptive events, such as plasma jets and powerful coronal mass ejections (CMEs).

Descrizione progetto (Article)

CMEs are clouds of magnetic fields and plasma - a gas heated to the point that it is composed of positively charged ions and free electrons. While there is a plethora of observations of these explosive outbursts of plasma from the Sun, their analysis has not yet been conclusive on the mechanisms underlying the origin of these drivers of Space Weather.

With the help of state-of-the-art computer simulations, scientists working on the project 'Solar dynamic phenomena as an astrophysical laboratory: Jets and coronal mass ejections' (JET-CME) have discovered an important piece of the puzzle. More precisely, their results show how and why the emergence of magnetic fields, from the Sun's interior into the solar surface and above, can trigger these eruptions.

Through 3D magnetohydrodynamic simulations, JET-CME scientists were able to reproduce how twisted bundles of magnetic flux rise from the solar interior and subsequently interact with pre-existing magnetic fields in the solar atmosphere. To perform these advanced numerical experiments of flux emergence, they used the parallel supercomputers at the University of St. Andrews (Scotland) and the University of Oslo (Norway).

By studying the process of magnetic flux emergence, scientists investigated also the (recurrent) emission of plasma jets. They found that reconnection between emerging and ambient magnetic fields in the solar atmosphere is actually the key process responsible for a variety of fast and hot plasma ejecta at various atmospheric heights. For instance, they found and studied the emission of fast (faster than 100 km per second) and hot (hotter than 1 million Kelvin) jets, which burst from the solar corona into the outer space.

These explosive phenomena, with implications for the heating of the corona, are observed in detail by various solar missions (e.g. the Solar Dynamics Observatory - SDO). However, even the most advanced instruments in the recent solar missions cannot capture the physical mechanisms underlying the origin of the above-mentioned explosive phenomena. A comparison of up-to-date observations with the results of computer simulations, allowed JET-CME scientists to reveal more about the dynamics of the Sun's atmosphere and the nature of various explosive events (fast eruptions and jets).

To expand on project findings, JET-CME scientists hope to employ the tested numerical models, to other more distant and exotic astrophysical environments, such as young stellar objects surrounded by accretion discs. Their aim is to study in the future the emission of plasma jets, as a universal physical process.