The Cassiopeia A nebula provides a special opportunity for improving our understanding of how massive stars explode since it is the remnant of the most recent instance (AD 1680) of such a supernova event (of which we are aware) within our own Galaxy. Its relative proximity (a distance of 2.9 kpc) makes it possible to study the source's structure and time evolution in sufficient detail and over a sufficiently broad spectral range (from X-rays to radio waves) that the important physical processes are becoming increasingly well-defined. Here we report how we have exploited the rapid time evolution of the source through a series of three high-resolution radio images spanning four years. These images have allowed us to recognize the previously unsuspected process which is in fact dominant in shaping the object. Tenuous clumps of intermediate velocity stellar ejecta are now continuously puncturing, from within, the decelerated shell swept up by the diffuse ejecta which once had the highest velocity.
[1]
P. Napier,et al.
The Very Large Array.
,
1980
.
[2]
S. Bergh,et al.
Optical studies of Cassiopeia A. VII. Recent observations of the structure and evolution of the nebulosity.
,
1985
.
[3]
M. Ryle,et al.
A New Intense Source of Radio-Frequency Radiation in the Constellation of Cassiopeia
,
1948,
Nature.
[4]
A. Bell.
Proper motions and temporal flux changes of compact features in Cassiopeia A at 5 GHz
,
1977
.
[5]
Ivan Rosenberg,et al.
Distribution of Brightness and Polarization in Cassiopeia A at 5.0 GHz
,
1970
.
[6]
R. Tuffs.
Secular changes within Cassiopeia A at 5 GHz–I
,
1986
.