A bipolar explosion shaped SN 1987A. The study: “Tracing the ejecta structure of SN 1987A: Insights and diagnostics from 3D MHD simulations” of S. Orlando (INAF – OAPA) appeared on A&A

Theoretical analysis of the properties of the cloud of stellar fragments (i.e., the ejecta) populating the innermost region of the supernova remnant SN 1987A reveals a highly asymmetric explosion, dominated by two bipolar jets.

The complex physics governing the core collapse of a massive star and the subsequent supernova explosion can be uncovered through detailed analysis of the physical properties of the ejecta produced by the explosion—particularly those in the inner regions, as long as they have not yet been hit by reverse shock waves traveling inward through the remnant.

Multiple observations of the SN 1987A supernova remnant—produced by the explosion of a blue supergiant in the Large Magellanic Cloud in 1987—show that the inner ejecta exhibit a strongly asymmetric morphology. In particular, the James Webb Space Telescope has revealed the presence of iron-rich ejecta with a distinctly bipolar structure, expanding at a velocity of about 2300 km/s. These ejecta are especially significant because they originated from the deepest layers of the progenitor star.

In a recent study published in Astronomy & Astrophysics, titled “Tracing the ejecta structure of SN 1987A: Insights and diagnostics from 3D MHD simulations”, a team of researchers led by astrophysicist S. Orlando (INAF – Osservatorio Astronomico di Palermo) developed and analyzed a magnetohydrodynamic model (i.e., one that accounts for the interaction between matter and magnetic fields) of SN 1987A, simulating its evolution from the supernova explosion to the formation of the remnant.

The model successfully reproduces the bipolar morphology of the iron-rich ejecta observed by the James Webb Space Telescope, demonstrating that such structures result from a highly asymmetric explosion. The expansion of these ejecta was further accelerated by the radioactive decay of nickel into iron—a process that heated the inner material of the remnant, increased its pressure, and contributed to the formation of a “Ni-bubble”.

The model also enabled predictions about the evolution of X-ray emission from the ejecta in the coming years. In particular, the interaction between reverse shock waves and the outer iron-rich ejecta has heated the material to high temperatures, causing it to emit X-rays. This emission has been increasing since 2021 and is expected to rise further as the innermost ejecta are progressively struck by the reverse shocks. Future observations with X-ray telescopes, such as the XRISM satellite by the Japan Aerospace Exploration Agency (JAXA), will provide valuable diagnostics for studying the physical properties of the innermost ejecta.

The cover image (click here to view in full) shows:

on the left panel, the image of SN 1987A taken by the NIRCam instrument aboard the James Webb Space Telescope;
in the central panel, the density distribution of the supernova remnant, including the iron-rich ejecta, as predicted by a 2020 model developed by S. Orlando’s team;
on the right panel, the current morphology of the remnant, as predicted by the new model presented in this study.