Re: supernova rings

Glenn R. Morton (
Thu, 30 Apr 1998 05:42:38 -0500

At 11:19 PM 4/29/98 -0600, Bill Payne wrote:
>Thanks for the info Paul. Now, please help me understand this. SN1987A
>exploded some time in the past. Immediately, light from the explosion
>radiated out in all directions. Some of the light travelled in a
>straight line to the earth and arrived here in 1987. Some of the light
>travelled perpendicular to the SN1987A-earth path, hit the rings, and
>then bounced off the rings and travelled to the earth, arriving in
>February, 1988. If the echo was one light year behind the initial light
>that travelled in a direct straight line from the supernova to the
>earth, then it would seem to me (and I think Glenn as well) that the
>ring radius is one light year. If the ring radius were thousands of
>light years, then the echo should be thousands of light years after the
>1987 explosion.

>What am I missing?

two things. The light from the light echo left the star several hundred or
thousands of years PRIOR to the supernova explosion. This light is merely
reflection. The light from the inner ring is not actually quite the same as
a light echo. it is radiation from a heated body of gas. The gas in the
inner ring was heated by x-rays from the supernova. Now, it glows on its
own, which is why it is so much brighter than the light echo.

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