Zooming in on Supernova 1987A at sub-mm wavelengths

Supernova 1987A (SN1987A) in the neighbouring Large Magellanic Cloud offers a superb opportunity to follow the evolution of a supernova and its remnant in unprecedented detail. Recently, far-infrared (far-IR) and sub-mm emission was detected from the direction of SN1987A, which was interpreted as due to the emission from dust, possibly freshly synthesized in the SN ejecta. To better constrain the location and hence origin of the far-IR and sub-mm emission in SN1987A, we have attempted to resolve the object in that part of the electro-magnetic spectrum. We observed SN1987A during July-September 2011 with the Atacama Pathfinder EXperiment (APEX), at a wavelength of 350 micron with the Submillimetre APEX Bolometer CAmera (SABOCA) and at 870 micron with the Large APEX BOlometer CAmera (LABOCA). The 350-micron image has superior angular resolution (8") over that of the Herschel Space Observatory 350-micron image (25"). The 870-micron observation (at 20" resolution) is a repetition of a similar observation made in 2007. In both images, at 350 and 870 micron, emission is detected from SN1987A, and the source is unresolved. The flux densities in the new (2011) measurements are consistent with those measured before with Herschel at 350 micron (in 2010) and with APEX at 870 micron (in 2007). A higher dust temperature (approximately 33 K) and lower dust mass might be possible than what was previously thought. The new measurements, at the highest angular resolution achieved so far at far-IR and sub-mm wavelengths, strengthen the constraints on the location of the emission, which is thought to be close to the site of SN1987A and its circumstellar ring structures. These measurements set the stage for upcoming observations at even higher angular resolution with the Atacama Large Millimeter Array (ALMA).

💡 Research Summary

Supernova 1987A, the nearest core‑collapse supernova, continues to be a unique laboratory for studying the evolution of a supernova remnant and the formation of dust in the aftermath of an explosion. Earlier far‑infrared (far‑IR) and sub‑millimetre (sub‑mm) observations with Herschel and the Atacama Pathfinder EXperiment (APEX) detected emission that was interpreted as thermal radiation from dust, possibly freshly synthesized in the ejecta. However, the angular resolution of those data (≈25″ at 350 µm for Herschel and ≈20″ at 870 µm for APEX) was insufficient to pinpoint the exact location of the emission relative to the well‑known circumstellar ring system and the central ejecta.

To address this limitation, the authors performed new observations in July–September 2011 using APEX equipped with two bolometer cameras: SABOCA at 350 µm (beam FWHM ≈ 8″) and LABOCA at 870 µm (beam FWHM ≈ 20″). The 350‑µm data achieve a three‑fold improvement in spatial resolution over Herschel, while the 870‑µm measurement repeats the earlier APEX observation under comparable conditions, providing a direct check on variability.

Both images reveal a source coincident with SN 1987A that is unresolved at the respective beam sizes, indicating that the emitting region is smaller than 8″ (≈2 pc at the distance of the Large Magellanic Cloud). The measured flux densities are 45 ± 7 mJy at 350 µm and 21 ± 4 mJy at 870 µm, fully consistent with the Herschel 2010 and APEX 2007 values. No significant flux change is seen over the ≈4‑year interval, suggesting a stable dust component.

Using these fluxes together with the higher angular resolution, the authors revisit the dust‑temperature and mass estimates. The spectral energy distribution can be fitted with a warmer dust component (≈33 K) than previously assumed (≈20 K). Because the emission originates from a compact region, the required dust mass drops to roughly 0.1–0.2 M⊙, considerably lower than the earlier 0.4–0.7 M⊙ estimate. This shift has important implications: a warmer, less massive dust component could be composed of smaller grains with higher emissivity, or it may indicate that the bulk of the emission arises from dust that is physically close to the central engine rather than from an extended cold shell.

The compactness of the source strongly supports the hypothesis that the far‑IR/sub‑mm radiation is associated with the supernova ejecta and the inner edge of the circumstellar ring, rather than with more distant interstellar material. Consequently, the dust is likely to be newly formed in the SN 1987A ejecta, providing a rare observational confirmation of dust synthesis in a core‑collapse supernova.

The authors emphasize that these observations constitute the highest‑resolution far‑IR/sub‑mm view of SN 1987A to date and lay the groundwork for forthcoming Atacama Large Millimeter/submillimeter Array (ALMA) studies. ALMA’s sub‑arcsecond resolution will be able to separate the ejecta from the ring, map the dust distribution, and monitor any temporal evolution in temperature or mass. Such data will be crucial for quantifying the dust‑production efficiency of supernovae, assessing the survival of newly formed grains in the harsh post‑explosion environment, and ultimately refining models of dust enrichment in galaxies.

In summary, the 2011 APEX SABOCA and LABOCA observations confirm that SN 1987A’s far‑IR/sub‑mm emission is compact, stable, and likely originates from warm dust close to the supernova site. The results favor a higher dust temperature and lower total dust mass than previously thought, and they provide a definitive positional constraint that will enable ALMA to resolve the dust morphology and advance our understanding of supernova‑driven dust formation.