Richard McCray
Research Interests
- I have worked on a wide variety of topics in theoretical astrophysics, mostly
having to do with the dynamics and kinetics of diffuse gas and the formation
of spectra in various astrophysical systems, including interstellar gas, active
galactic nuclei, binary X-ray systems, and supernova explosions. I also observe
these systems with spacecraft such as the Hubble Space Telescope (HST) and
the Chandra X-ray telescope.
- My primary interest during the past 15 years has been SN1987A. Because it
is the brightest supernova since Kepler's supernova SN1604, we have a far
better view of SN1987A than of any other supernova. We have been able to observe
the development of its entire electromagnetic spectrum, from radio to gamma
rays, for more than ten years. Thanks to HST, we have images that resolve
the expanding debris of the supernova and its remarkable system of three rings
of circumstellar gas.
- My research on SN1987A has two main goals. The first is to understand what
its spectrum tells us about the physical properties of the debris - its distribution
in element composition, temperature, and density. These are essential clues
to the explosion mechanism of supernovae and to the role of supernovae in
producing the heavy elements in the universe. To do this, I use computers
to model the atomic, molecular, and radiative processes by which gamma rays
from newly-synthesized radioactive elements are degraded into the X-ray, ultraviolet,
optical, and infrared photons that escape from the debris and are observed
at Earth.
- The second goal of my research on SN1987A is to understand the nature of
its circumstellar ring system. We suspect that these rings were expelled by
the supernova progenitor star some 20,000 years before it exploded, but we
don't understand the expulsion mechanism. The visible rings are probably only
the ionized inner surfaces of a much greater mass of gas that we cannot see,
because the supernova flash did not produce enough ionizing radiation to illuminate
it. However, in 1991, Ding Luo and I predicted that the blast wave from the
supernova would strike the inner ring in about 1997, and that when it did,
the ring would brighten by a factors ~ 1000. Later, in 1997, Kazik Borkowski,
John Blondin, and I predicted that we would also be able to see Lyman-alpha
and H-alpha emission from the fast moving supernova debris as it crossed a
shock front near the ring.
- All of these predictions are coming true. In 1997, using the Space Telescope
Imaging Spectrograph, we saw the predicted Lyman-alpha emission from the shock
front. The observed intensity was close to the value we predicted. Also, with
the Wide Field Camera on the HST, we saw a rapidly brightening "hot spot"
on the inner ring, evidently marking the first place where the supernova blast
wave struck the inner ring (see the image above). Now, in 2002, we see more
than a dozen hot spots all around the ring. We expect that soon (say, within
5 years) the hotspots will merge so that the entire ring will be ablaze as
it is overtaken by the supernova blast wave. This is the first time in history
that astronomers can witness the birth of a supernova remnant in real time
as the event unfolds. At the moment, we are observing the development of this
crash intensively with the Hubble Space Telescope and with the Chandra and
XMM X-ray observatories, and we are interpreting these observations in terms
of hydrodynamic models for the shock interaction coupled with models for the
radiation emission by the shocked gas.
- We are also developing theoretical models to predict an exciting new phenomenon
connected with this event. The shock interaction from the impact of the debris
of SN1987A with the circumstellar ring is a new and rapidly brightening source
of ionizing radiation. This radiation will propagate ahead of the shock and
will ionize and heat the circumstellar gas, including the inner and outer
rings and other gas which was expelled by the supernova progenitor and has
remained invisible up to now. The gas will begin to glow as a result, so we
should see the entire system begin to light up over the next decade or so.
- For more details and images, see the section on SN1987A
in my hypertext.
-
- See RECENT PAPERS
Last modified August 28, 2002 by dick
http://jilawww.colorado.edu/~dick