The light echo of supernova 1987A
AAO image reference AAT 66.    « Previous || Next »

The light echo of supernova 1987A, light_echo.jpg
Top left is NE. Image width is about 5.5 arc min
Image and text © 1989-2010, Australian Astronomical Observatory, photograph by David Malin.

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 and after the supernova appeared. The only major difference between them is the light echo itself. However, the bright stars do not cancel perfectly and appear black, while in other, bright parts of the image, the photographic noise does not cancel either. 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 ellise 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.

Related Images
AAT 48.   The Tarantula Nebula and supernova 1987a in the Large Magellanic Cloud
AAT 48b. Supernova 1987A, the star, in March 1987
AAT 49.   The Tarantula Nebula in the LMC, before supernova SN1987A
AAT 50.   Supernova 1987A, before and after images
AAT 67.   Supernova 1987a after 4 years
Constellation of Dorado (external site)

For details of photographic exposure, search technical table by AAT reference number.

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Updated by David Malin, 2010, August 1