Investigating the formation of post-coronal mass ejection plasmoids observed by the Metis coronagraph on board Solar Orbiter

Coronal mass ejections (CMEs) are complex transient solar phenomena often associated with solar flares, large-scale current sheets (CS), and the formation of dense plasma structures, known as plasmoids or plasma blobs. Multiwavelength observations are required to study the properties, onset, and evolution of these structures. We studied the properties of multiple plasma blobs that are likely related with magnetic reconnection that continues after the transit of a CME over the solar west limb on November 9, 2021, using the observations acquired by the Solar Orbiter/Metis coronagraph. Metis visible-light (VL) images show the propagation of plasma structures around the main CME propagation latitude, as also observed by the LASCO coronagraphs on board SOHO. The main goal was to study the properties of these plasmoids, using the two Metis observation channels, VL broadband and the ultraviolet (UV) Lyman-α line, to estimate the energies involved and infer the formation heights of the blobs under the hypothesis that they might be blobs that formed through a tearing instability along the post-CME CS. We then identified observational signatures of their formation in the images. H i We identified and tracked five blobs using VL images and measured their propagation speed. For the three brightest, we derived the electron densities and then calculated the kinetic, potential, and thermal energy densities that were dragged by the blobs. The five blobs were not visible in the UV images. A comparison between the intensities observed by Metis and the theoretical intensities expected in the UV channel enabled us to constrain the plasma temperature and the associated thermal energy density of the blobs, however. These estimates were used to infer the most probable heliocentric distances and times of the blob formation. The blob speeds were between 550 and 770 km s^ -1 and densities between 8.2 ⋅ 10^ 4 and $ 3.6 ⋅ 10^ 5 -3 $. We estimated that the blob formation region ranged from 3.5 to 5.0 R_⊙, that is, outside the Metis field of view, which extended between 5.3 and 9.6 R_⊙ on that day, but inside the LASCO-C2 field of view, as supported by the observed morphology. We characterize the evolution of post-CME blobs observed in the VL channel of Metis in terms of their energetics and formation heights, and, using simultaneous observations in the UV channel, in which the blobs were not visible, we also infer a constraint on the plasma temperature inside them. Our results suggest that some blobs formed inside the LASCO-C2 field of view (from 2 to 6 R_⊙), while other blobs likely formed in the inner corona (below 2 R_⊙) and were observed higher up by the LASCO and Metis coronagraphs.