Structure of the radio remnant of supernova 1987A

Abstract

SUPERNOVA 1987A in the Large Magellanic Cloud, the closest known supernova for 400 years, offers unprecedented opportunities for the detailed study of the evolution of a supernova at all wavelengths. The radio remnant of SN1987A was detected in July 1990 (ref. 1), since when it has steadily brightened at all radio frequencies². Its present brightness and size are now sufficient for its structure to be resolved. Here, we present high-resolution images of the remnant at a frequency of 8.8 GHz, which reveal a spherical, shell-like structure with a radius of 0.6 arcsec (4 × 10¹⁷ cm, assuming a distance of 50 kpc) and an additional component that is aligned with the optical ring (of somewhat larger radius) imaged by the Hubble Space Telescope³. We suggest that this alignment arises from an interaction between the expanding shock wave and dense clouds sheared from the ring. The mean expansion velocity of the supernova shock front, as measured from its current radio size, is ∼30,000 km s⁻¹. Observations made over 600 days suggest, however, that either the remnant is rapidly changing shape or that the expansion velocity is decreasing more rapidly than expected.