Re: supernova rings

Glenn R. Morton (
Thu, 30 Apr 1998 20:23:42 -0500

At 01:02 PM 4/30/98 -0600, Bill Payne wrote:
>Glenn R. Morton wrote:
>> 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.
>OK, then if that is the case, how do we know the diameter of the outer
>ring? And why did the outer (and inner) ring only show up in February,
I am not going to look this up but I bet I can surmise a very good reason
for this. First the light echo is very weak and the photos must be
processed to observe them. The fact that there was no reason (no
supernova) prior to 1987 there was little reason to look for them.

Secondly, once you know the diameter of the inner ring, you can calculate
the distance to the supernova (pure trigonometry). And once you know that
distance you can use it and the angular diameter of the light echo to
calculate the size of the light echos. Simple trig.

> 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.
>OK, so you're saying the inner ring has a radius of 1 light year because
>its "radiation echo" is 1 year behind the explosion and first sighting
>of the direct straight-line path of light from the explosion? Is that

Since I didn't have time early this morning to search my files, here is
documentation that the inner ring was dark prior to the explosion and it
explains what I meant early this morning.

"The ring, made of material ejected from the supernova's
progenitor star in its red supergiant phase, already girdled the
star five thousand years before it exploded. But it was cold and
dark. Only when the radiation from the supernova blast reached
the ring and heated it to 2 X 10^4 K did it become observable to
ultraviolet and visible-light telescopes."
~Bertram Schwarzschild, "Ring Around 1987 Supernova Provides a
New Yardstick,", Physics Today, February 1991, p. 20.

The outer rings were found after the entire astronomical community turned
their telescopes on this single star.

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