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JWST observations of the young Galactic supernova remnant Cassiopeia A revealed an unexpected structure seen as a green emission feature in colored composite MIRI F1130W and F1280W images—hence dubbed the Green Monster—that stretches across the central parts of the remnant in projection. Combining the kinematic information from NIRSpec and the MIRI Medium Resolution Spectrograph with the multiwavelength imaging from NIRCam and MIRI, we associate the Green Monster with circumstellar material (CSM) that was lost during an asymmetric mass-loss phase. MIRI images are dominated by dust emission, but their spectra show emission lines from Ne, H, and Fe with low radial velocities indicative of a CSM nature. An X-ray analysis of this feature in a companion paper supports its CSM nature and detects significant blueshifting, thereby placing the Green Monster on the nearside, in front of the Cas A supernova remnant. The most striking features of the Green Monster are dozens of almost perfectly circular 1″–3″ sized holes, most likely created by interaction between high-velocity supernova ejecta material and the CSM. Further investigation is needed to understand whether these holes were formed by small 8000–10,500 km s−1 N-rich ejecta knots that penetrated and advanced out ahead of the remnant’s 5000–6000 km s−1 outer blast wave or by narrow ejecta fingers that protrude into the forward-shocked CSM. The detection of the Green Monster provides further evidence of the highly asymmetric mass loss that Cas A’s progenitor star underwent prior to its explosion.

Context. While supernova remnants (SNRs) are observed to produce up to 1 M\\(_\\) of dust, the amount of dust destroyed by the forward shock (FS) is poorly constrained, raising the question whether they are net dust producers or destroyers. Aims. We aim to estimate the dust destruction efficiency of SNR FSs in a realistically turbulent interstellar medium (ISM) during their most destructive phase, and assess dust shielding by high density filaments during this period. Methods. We run 3D turbulence simulations for different turbulent Mach numbers (0-3) and average ISM densities (1-100 cm\\(^-3\\)) to resemble observations of the turbulent ISM. We then set off a supernova to trace its 3D magnetohydrodynamical evolution for 10 kyr. Finally, we run post-processing simulations to study the dust transport and destruction by the SNR FS, considering gas and plasma drag, kinetic and thermal sputtering, and grain-grain collisions, and either silicate or carbonaceous dust. Results. The dust destruction rate of the FS strongly depends on the average ISM density and turbulence strength, varying between 27-92% (0.85-11.0 M\\(_\\)) in the studied 10 kyr. Overall, dust is less efficiently destroyed in a low density medium (1 cm\\(^-3\\), 27-57%) than in intermediate (10 cm\\(^-3\\), 46-92%) and high densities (100 cm\\(^-3\\), 73-87%). The FS destroys 8-34% less dust in high Mach turbulence compared to a homogeneous medium. Furthermore, carbonaceous grains are more robust (up to 21% more) than silicates. Conclusions. Filaments can partly shield dust from destruction in the first 10 kyr, however, always more than 0.85 M\\(_\\) of dust is destroyed, making most SNRs dust sinks under the conditions explored in this work. The destruction efficiency of the SNRs with less than 1 M\\(_\\) of destroyed dust has not yet plateaued so that they are most likely also net dust destroyers by the end of their lifetime.

Context: The recently discovered spherical eROSITA bubbles arise up to a latitude of \\(\\)80-85 in the X-ray regime of the Milky Way halo. Similar to the \\(\\)-ray Fermi bubbles, they evolve around the Galactic center, making a common origin plausible. However, the driving mechanism and evolution of both bubbles are still under debate. Aims: We investigate whether hydrodynamic energy injections at the Galactic center, such as e.g. tidal disruption events (TDEs), could have inflated both bubbles. The supermassive black hole Sagittarius A* is expected to tidally disrupt a star every 10-100 kyr, potentially leading to an outflow from the central region that drives a shock propagating into the Galactic halo due to its vertically declining density distribution, ultimately forming a superbubble that extends out of the disk similar to the eROSITA and Fermi bubbles. Methods: We model TDEs in the Galaxy using three-dimensional hydrodynamical simulations, considering different Milky Way mass models and TDE rates. We then generate synthetic X-ray maps and compare them with observations. Results: Our simulation results of a \\(\\)-model Milky Way halo show that superbubbles, blown for 16 Myr by regular energy injections at the Galactic center that occur every 100 kyr, can have a shape, shell stability, size, and evolution time similar to estimates for the eROSITA bubbles, and an overall structure reminiscent of the Fermi bubbles. The \\(\\)-rays in our model would stem from cosmic ray interactions at the contact discontinuity, where they were previously accelerated by first-order Fermi acceleration at in situ shocks. Conclusions: Regular TDEs in the past 10-20 Myr near the Galactic center could have driven an outflow resulting in both, the X-ray emission of the eROSITA bubbles and the \\(\\)-ray emission of the Fermi bubbles.

Context. While supernova remnants (SNRs) are observed to produce up to 1 M\\(_\\) of dust, the amount of dust destroyed by the forward shock (FS) is poorly constrained, raising the question whether they are net dust producers or destroyers. Aims. We aim to estimate the dust destruction efficiency of SNR FSs in a realistically turbulent interstellar medium (ISM) during their most destructive phase, and assess dust shielding by high density filaments during this period. Methods. We run 3D turbulence simulations for different turbulent Mach numbers (0-3) and average ISM densities (1-100 cm\\(^-3\\)) to resemble observations of the turbulent ISM. We then set off a supernova to trace its 3D magnetohydrodynamical evolution for 10 kyr. Finally, we run post-processing simulations to study the dust transport and destruction by the SNR FS, considering gas and plasma drag, kinetic and thermal sputtering, and grain-grain collisions, and either silicate or carbonaceous dust. Results. The dust destruction rate of the FS strongly depends on the average ISM density and turbulence strength, varying between 27-92% (0.85-11.0 M\\(_\\)) in the studied 10 kyr. Overall, dust is less efficiently destroyed in a low density medium (1 cm\\(^-3\\), 27-57%) than in intermediate (10 cm\\(^-3\\), 46-92%) and high densities (100 cm\\(^-3\\), 73-87%). The FS destroys 8-34% less dust in high Mach turbulence compared to a homogeneous medium. Furthermore, carbonaceous grains are more robust (up to 21% more) than silicates. Conclusions. Filaments can partly shield dust from destruction in the first 10 kyr, however, always more than 0.85 M\\(_\\) of dust is destroyed, making most SNRs dust sinks under the conditions explored in this work. The destruction efficiency of the SNRs with less than 1 M\\(_\\) of destroyed dust has not yet plateaued so that they are most likely also net dust destroyers by the end of their lifetime.

JWST observations of the young Galactic supernova remnant Cassiopeia A revealed an unexpected structure seen as a green emission feature in colored composite MIRI F1130W and F1280W images - hence dubbed the Green Monster - that stretches across the central parts of the remnant in projection. Combining the kinematic information from NIRSpec and MIRI MRS with the multi-wavelength imaging from NIRCam and MIRI, we associate the Green Monster with circumstellar material that was lost during an asymmetric mass-loss phase. MIRI images are dominated by dust emission but its spectra show emission lines from Ne, H and Fe with low radial velocities indicative of a CSM nature. An X-ray analysis of this feature in a companion paper (Vink et al. 2024) supports its CSM nature and detects significant blue shifting, thereby placing the Green Monster on the near side, in front of the Cas A SN remnant. The most striking features of the Green Monster are dozens of almost perfectly circular 1\" - 3\" sized holes, most likely created by interaction between high-velocity SN ejecta material and the CSM. Further investigation is needed to understand whether these holes were formed by small 8000-10500 km/s N-rich ejecta knots that penetrated and advanced out ahead of the remnant's 5000 - 6000 km/s outer blastwave, or by narrow ejecta fingers that protrude into the forward-shocked CSM. The detection of the Green Monster provides further evidence of the highly asymmetric mass-loss that Cas A's progenitor star underwent prior to explosion.