> "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."
And the ring became heated and therefore visible by February, 1998,
correct? Therefore, the inner ring has a radius of one light year?
This brings me back to my original question. Quoting from Goldsmith:
"Figure 20 shows a photograph (printed as a negative to bring out more
detail) taken with the 3.6-meter reflecting telescope at the European
Southern Observatory in Chile, using a state-of-the-art imaging system
that reveals details never before observable. In this photograph, the
bulk of the light from SM 1987A has produced the overexposed black area
at the center. The two concentric circles are the light echoes,
scattered light that has taken several months longer to reach us than
the light from the central image."
"Astronomers have been quick to make mathematical models of the
situation that gives rise to the light echoes. Their calculations shwo
that the inner ring arises from dust located about 400 light-years from
SN 1987A, and the outer ring from dust grains some 1,000 light-years
from the supernova, all still well within the Large Magellanic Cloud."
(_Supernova! - The Exploding Star of 1987_, Donald Goldsmith, St.
Martin's Press, 1989, p 151)
Goldsmith's statements are simply contradictory as far as I can see. He
says "The two concentric circles are the light echoes, scattered light
that has taken several months longer to reach us than the light from the
central image," and then he says "the inner ring arises from dust
located about 400 light-years from SN 1987A, and the outer ring from
dust grains some 1,000 light-years from the supernova."
If the inner ring is 400 light-years from SN 1987A, then the light from
SN 1987A will travel 400 years before reflecting off the inner ring, and
it will reach the earth 400 years later than the first straight-line
light, not one year later as observed.
According to the proportions in the photograph Goldsmith shows on p 152,
the outer ring can't be much more than 2 light-years from SN 1987A, if
the inner ring is one light year out. A "cross-section" through the
photo looks like:
X <--- Outer Ring
X <--- Inner Ring
X <--- SN 1987A
X <--- Inner Ring
X <--- Outer Ring
Now, if the rings were visible all the time but only noticed after all
of the world's telescopes were turned on the supernova, then the
yardstick flies out the window. You no longer have the light echo to
use to calibrate the ring diameter.
I had thought the explanation would be quite simple, but I don't think
it has been resolved yet.
Bill