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The light echo of SN 1987A, February, 1989

Date created: 1989-02-16

Tags: galaxy, dust, supernova, SN1987A

When supernova 1987A was seen to explode in the Large Magellanic Cloud, the Milky Way's nearest companion galaxy, the brilliant flash of light from the self-destructing star had taken about 170,000 years to arrive at the telescope. Some light was deflected by two sheets of dust near the supernova, and is seen after the star has faded away because the reflected light covers a longer path to reach us. The dust responsible for the rings seen here lies in two distinct sheets, about 470 and 1300 light years from the supernova, close to our line of sight to it.

The colour picture was made by photographically subtracting negative and positive images of plates of the region taken before (February 1984) and after (December 1990) the supernova appeared. The only major difference between them is the light echo itself. Everything that cancels perfectly appears black, while elsewhere the cancellation is less than perfect, mainly due to photographic 'noise' in the nebulosity. Despite this the image is an accurate reproduction of the colour of the extremely faint light echo, which in turn reflects the yellow colour of the supernova when it was at its brightest, in May, 1987.

There's an article by David Malin and David Allen describing the phenomenon in Sky and Telescope magazine for January, 1990 (p22) and here is a diagram and caption from the article showing how the light echoes were formed. From our point of view, at the focus of the long ellipse shown in the diagram, the light echoes appear to expand with time and we were able to record this expansion in a series of six images, the last being 1440 days (almost five years) after the appearance of the supernova.

Top left is NE. Image width is about 5.5 arc min.

Credit: David Malin

© Australian Astronomical Observatory