supernova rings

Paul Arveson (
Wed, 6 May 1998 12:05:49 -0400

I sent our question to one of the Principal Investigators and received
this response (at bottom). Sorry about the confusion of my answer:


>We are having difficulty interpreting the geometry of the SN1987A
>supernova rings in regards to the speed of light. Can you relay this
>to the investigators involved, or give me their email addresses?
>(Chris Burrows, Peter Garnavich, et al.)
>Thank you.
>At 1:19 AM -0400 4/30/98, Bill Payne wrote:
>>Paul Arveson wrote:
>>> These captions (also see the pictures) indicate that the rings
>>> were formed from gas shed by the star thousands of years before
>>> it exploded in a supernova. The rings are now several
>>> thousands of light years in radius. Light from the supernova explosion
>>> lit up the dust in the rings, although the rings are now
>>> fading because the central source is fading. The pictures show
>>> this.
>>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?
Date: Tue, 05 May 1998 12:04:13 -0500 (EST)
From: "CHRIS (410)516-6562" <>
Subject: Re: CNSHD65217 Re: Re: supernova rings
Mime-Version: 1.0

You are absolutely right that the light from the rings is delayed... but the
rings are only a few light years across not thousands as you seem to assume...
so there was time for the whole structure to be lit up before our HST
observations... In fact this time delay has been used to derive the best
distance yet to the Magellanic clouds...The time it took for the rings to
illuminate, together with their apparent angular size gives us the distance...

Hope this answers your question.



Paul Arveson, Code 724, Research Physicist, Signatures Directorate
Naval Surface Warfare Center, Carderock Division
9500 MacArthur Blvd., West Bethesda, MD 20817-5700
(301) 227-3831 (301) 227-4511 (FAX)