STRUCTURE OF THE RADIO REMNANT OF SUPERNOVA-1987A

SUPERNOVA 1987A in the Large Magellanic Cloud, the closest known super nova for 400 years, offers unprecedented opportunities for the detaile d 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 h as steadily brightened at all radio frequencies2. Its present brightne ss 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 x 10(17) cm, assuming a distance of 50 kpc) and an addi tional component that is aligned with the optical ring (of somewhat la rger radius) imaged by the Hubble Space Telescope3. We suggest that th is alignment arises from an interaction between the expanding shock wa ve and dense clouds sheared from the ring. The mean expansion velocity of the supernova shock front, as measured from its current radio size , is approximately 30,000 km s-1. Observations made over 600 days sugg est, however, that either the remnant is rapidly changing shape or tha t the expansion velocity is decreasing more rapidly than expected.