Hubble Space Telescope images of SN 1987A: Evolution of the ejecta and the equatorial ring from 2009 to 2022

TL;DR

This study uses Hubble Space Telescope images from 2009 to 2022 to analyze the evolution of SN 1987A's ejecta and equatorial ring, revealing fading of the ring, brightening of ejecta, and no detection of a compact object.

Contribution

First comprehensive multi-epoch HST imaging analysis of SN 1987A's ejecta and ring evolution from 2009 to 2022, including constraints on the central compact object.

Findings

The equatorial ring has continued fading since 8200 days post-explosion.

Ejecta brightened until about 11000 days, with asymmetrical brightness suggesting X-ray influence.

No detection of a compact object, setting an upper flux limit and implications for the remnant's core.

Abstract

Supernova (SN) 1987A offers a unique opportunity to study how a spatially resolved SN evolves into a young supernova remnant (SNR). We present and analyze Hubble Space Telescope (HST) imaging observations of SN 1987A obtained in 2022 and compare them with HST observations from 2009 to 2021. These observations allow us to follow the evolution of the equatorial ring (ER), the rapidly expanding ejecta, and emission from the center over a wide range in wavelength from 2000 to 11 000 AA. The ER has continued to fade since it reached its maximum ~8200 days after the explosion. In contrast, the ejecta brightened until day ~11000 before their emission levelled off; the west side brightened more than the east side, which we attribute to the stronger X-ray emission by the ER on that side. The asymmetric ejecta expand homologously in all filters, which are dominated by various emission lines from hydrogen, calcium, and iron. From this overall similarity, we infer the ejecta are chemically well-mixed on large scales. The exception is the diffuse morphology observed in the UV filters dominated by emission from the Mg II resonance lines that get scattered before escaping. The 2022 observations do not show any sign of the compact object that was inferred from highly-ionized emission near the remnant's center observed with JWST. We determine an upper limit on the flux from a compact central source in the [O III] HST image. The non-detection of this line indicates that the S and Ar lines observed with JWST originate from the O free inner Si - S - Ar rich zone and/or that the observed [O III] flux is strongly affected by dust scattering.