Molecular bipolar outflow in SN 1987A supports the jittering-jets explosion mechanism

Abstract

I examine high-quality CO and SiO molecular maps of the core-collapse supernova (CCSN) remnant SN 1987A from the literature and find that the molecular gas exhibits a bipolar structure, correlated with the visible bipolar morphology (termed the keyhole) and the bipolar morphology of the iron emission map. The keyhole has a morphology similar to that of many jet-shaped pairs of bubbles in cooling-flow clusters of galaxies and planetary nebulae. Therefore, the findings of this study, which make the bipolar structure of SN 1987A robust, strengthen the claim that a pair of energetic jets shaped the keyhole and its surroundings. According to the jittering-jets explosion mechanism (JJEM), this pair of jets was the most energetic of several pairs that exploded SN 1987A. This study adds to the accumulating evidence that the JJEM is the primary explosion mechanism of CCSNe, responsible for the majority, or even all, CCSNe.

Figures (4)

• Figure 1: A figure adapted from Larssonetal2023, presenting images of the [Fe i] $1.443 {~\rm \mu m}$ emission line in Doppler velocity windows, as indicated. The dashed white line shows the position of the equatorial ring that the star lost $\simeq 20,000 {~\rm yr}$ before explosion. I added the red lines and the names of the outflow components: 'Fe' indicates that the components are identified in the [Fe i] $1.443 {~\rm \mu m}$ line, 'N' and 'S' mark north and south, respectively, and the last letter indicates whether the component is blueshifted, redshifted, or has about zero Doppler shift. The observation was on an age of 12,927 days after the explosion; one pixel in the image $0.1^{\prime \prime}=0.024 {~\rm pc}$, corresponds to $664 {~\rm km} {~\rm s}^{-1}$ in the freely expanding ejecta, for the distance to the LMC of $49.6 {~\rm kpc}$ that Larssonetal2023 assumed.
• Figure 2: The four large panels are adapted from Wessonetal2026. The two upper panels show 3D intensity maps of CO ($J=2-1$) emission, and the two lower panels show 3D intensity maps of SiO ($J=5-4$) emission. The left panel shows the plane of the sky, and in the right panel, Earth is to the right (red arrows point towards Earth). The plane of the equatorial ring is indicated in blue. Blue regions are above the equatorial ring plane, and green material is below it. The orange point marks the explosion's position. Each side of a panel is 40,000 AU. I copied the four-line structures from Figure \ref{['Fig:DopplerShift']}, but the lengths of the lines here are $0.67$ times those in Figure \ref{['Fig:DopplerShift']}. I also added the orange arrow in the left panels, which bisects the angle between outflow components FeNR and FeNB, and the two pink arrows in the lower-right panel to emphasize the bipolar structure of the molecular distribution. The inset between the two large lower panels is a figure adapted from BearSoker2018, an image from Abellanetal2017 showing CO ($J=2-1$) in red, SiO ($J=5-4$) in red, and H$\alpha$ in blue, i.e., the equatorial ring. The marking of the jet-like feature is from BearSoker2018, who already identified the molecular south outflow.
• Figure 3: Images adapted from Wessonetal2026, with my identification of the four outflow components. (a) Bright CO (dark purple-orange) and SiO (dark purple-green) emission overlaid with the [Fe i] (faint blue to yellow-red) emission that Wessonetal2026 obtained from Larssonetal2023. Only the regions with intensity above twice the noise threshold are shown by Wessonetal2026. (b) A transparent full CO map from Figure \ref{['Fig:Molecular1']}, which I overlaid on the image from panel (a). (c) A transparent full SiO map from Figure \ref{['Fig:Molecular1']}, which I overlaid on the image from panel (a).
• Figure 4: A figure adapted from Soker2024Keyhole which includes an HST/WFC3 image of SN 1987A in one filter from Rosuetal2024; north is up and east to the left. The field of view is $2.50^{\prime \prime} \times 2.25^{\prime \prime}$. The 'keyhole' is the north-south elongated bright structure within the equatorial ring. The identification of the rim, nuzzle, and two bubbles is from Soker2024CFs based on similarities to jet-inflated bubbles in cooling flow clusters of galaxies. Here I added the structure of the four red lines and the orange arrow from Figure \ref{['Fig:Molecular1']}, and at the same scale ($0.67$ times the scale of the four-line structure in Figure \ref{['Fig:DopplerShift']}).