Supernova Remnants
When a high mass star (final mass greater than 1.4 solar masses) collapses at the end of its life a supernova occurs. An enormous shock wave sweeps through the star at high speed, blasting away the various layers into space, leaving a neutron core and an expanding shell of matter known as a supernova remnant. This ejection of matter is much more violent than occurs in the planetary nebulae that mark the end of a low mass star, giving expansion speeds of 1.0E3 -1.0E4 km/s. Near the core of the remnant, electrons emit radiation (synchrotron radiation) as they spiral at relativistic speeds in the magnetic field from the neutron star. The ultraviolet portion of this radiation can ionize the outer filaments of the nebula. In addition the ejected matter sweeps up surrounding gas and dust as it expands producing a shock wave that excites and ionizes the gas. This plasma may reach temperatures of 1.0E4 to 1.0E6 K, but with densities of only about 1.0E7 particles per meter^3.
The Cygnus Loop
Photo Credit: Hubble Space Telescope image of the Cygnus Loop (public domain). Some artificial coloring was used to bring out special emission lines. For more information, or to get the original image, visit the Hubble Telescope Web Page for the Cygnus Loop.
The most famous supernova remnant is the Crab Nebula in Taurus (M1). The light of the inner core is from the synchrotron radiation, while in the outer regions there are many emission lines including the red glow from hydrogen. In other supernova remnants, such as the Veil in Cygnus (Cygnus Loop, above) only the emission lines in the wake of the expanding shock wave are visible. In the recent Supernova 1987A there is a ring of stellar material which was ejected before the supernova and a still small area of debris from the supernova explosion. In about 100 years, the expanding supernova remnant will reach the ring and tear through it.
In a recent supernova, SN1987A, the Hubble Space Telescope has discovered several rings in the expanding shock wave. Some of these rings remain a mystery. For a picture and more information see Hubble SN1987A.
Page contributed by G. Samuel Lightner.
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Princeton Plasma Physics Laboratory